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Before the emergence of SARS-CoV-2, the virus that causes COVID-19, influenza activity in the United States typically began to increase in the fall and peaked in February. During the 2021-22 season, influenza activity began to increase in November and remained elevated until mid-June, featuring two distinct waves, with A(H3N2) viruses predominating for the entire season. This report summarizes influenza activity during October 3, 2021-June 11, 2022, in the United States and describes the composition of the Northern Hemisphere 2022-23 influenza vaccine. Although influenza activity is decreasing and circulation during summer is typically low, remaining vigilant for influenza infections, performing testing for seasonal influenza viruses, and monitoring for novel influenza A virus infections are important. An outbreak of highly pathogenic avian influenza A(H5N1) is ongoing; health care providers and persons with exposure to sick or infected birds should remain vigilant for onset of symptoms consistent with influenza. Receiving a seasonal influenza vaccine each year remains the best way to protect against seasonal influenza and its potentially severe consequences.

From surveillance data of patients hospitalized with laboratory-confirmed influenza in the United States during the 2015–2016 through 2018–2019 seasons, initiation of antiviral treatment increased from 86% to 94%, with increases seen across all age groups. However, 62% started therapy ≥3 days after illness onset, driven by late presentation to care.

Background Influenza-associated hospitalization rates were low during the 2020–21 season. We describe influenza-associated hospitalization rates and prevalence of influenza and SARS-CoV-2 coinfection among patients hospitalized with influenza during 2021–22. Methods We used data from the Influenza Hospitalization Surveillance Network (FluSurv-NET), a population-based surveillance system for laboratory-confirmed influenza-associated hospitalizations active from October—April of each year. We calculated cumulative and weekly hospitalization rates per 100,000 population and compared preliminary rates during 2021–22 with prior season rates (2010–11 through 2020–21). We determined the proportion of influenza-associated hospitalizations with SARS-CoV-2 coinfection during 2021–22. Results During October 1, 2021—April 23, 2022, 3,262 influenza-associated hospitalizations were reported to FluSurv-NET; the cumulative hospitalization rate of 11.1 was higher than 2011–12 and 2020–21 season rates, but lower than rates observed during all other seasons since 2010–11 (Figure 1A). After peaking in the week ending January 1, 2022 (MMWR week 52), weekly hospitalization rates declined until the week ending February 19, 2022 (MMWR week 7) when they began to rise modestly, similar to patterns observed during several prior seasons (Figure 1B). Among the 3,262 hospitalizations, 87 (2.7%) had SARS-CoV-2 coinfection; the prevalence by age group was as follows: 0–17 years 3.4%, 18–49 years 2.8%, 50–64 years 3.5%, 65–74 years 2.5%, ≥ 75 years 1.6%. Among the 3,262 influenza-associated hospitalizations, the prevalence of SARS-CoV-2 coinfection by month (October 2021–April 2022), respectively, was 11.4%, 2.5%, 2.6%, 8.9%, 3.4%, 0.8%, and 0.5%. Conclusion SARS-CoV-2 coinfection was uncommon among patients hospitalized with influenza during 2021–22. Likely due to ongoing COVID-19 mitigation measures, the influenza-associated hospitalization rate during 2021–22 was lower than rates observed in most seasons in the decade preceding the COVID-19 pandemic. A late rise in weekly influenza hospitalization rates in 2021–22 might have been a result of relaxation of COVID-19 mitigation measures and/or a late season peak in influenza activity. Disclosures Evan J. Anderson, MD, GSK: Advisor/Consultant|GSK: Grant/Research Support|Janssen: Advisor/Consultant|Janssen: Grant/Research Support|Kentucky Bioprocessing, Inc: Data Safety Monitoring Board|MedImmune: Grant/Research Support|Medscape: Advisor/Consultant|Merck: Grant/Research Support|Micron: Grant/Research Support|NIH: Funding from NIH to conduct clinical trials of Moderna and Janssen COVID-19 vaccines|PaxVax: Grant/Research Support|Pfizer: Advisor/Consultant|Pfizer: Grant/Research Support|Regeneron: Grant/Research Support|Sanofi Pasteur: Advisor/Consultant|Sanofi Pasteur: Grant/Research Support|Sanofi Pasteur: Data Adjudication and Data Safety Monitoring Boards|WCG and ACI Clinical: Data Adjudication Board Maya Monroe, MPH, CDC -Emerging Infections Program: Grant/Research Support.

Objective:To estimate population-based rates and to describe clinical characteristics of hospital-acquired (HA) influenza.Design:Cross-sectional study.Setting:US Influenza Hospitalization Surveillance Network (FluSurv-NET) during 2011–2012 through 2018–2019 seasons.Methods:Patients were identified through provider-initiated or facility-based testing. HA influenza was defined as a positive influenza test date and respiratory symptom onset >3 days after admission. Patients with positive test date >3 days after admission but missing respiratory symptom onset date were classified as possible HA influenza.Results:Among 94,158 influenza-associated hospitalizations, 353 (0.4%) had HA influenza. The overall adjusted rate of HA influenza was 0.4 per 100,000 persons. Among HA influenza cases, 50.7% were 65 years of age or older, and 52.0% of children and 95.7% of adults had underlying conditions; 44.9% overall had received influenza vaccine prior to hospitalization. Overall, 34.5% of HA cases received ICU care during hospitalization, 19.8% required mechanical ventilation, and 6.7% died. After including possible HA cases, prevalence among all influenza-associated hospitalizations increased to 1.3% and the adjusted rate increased to 1.5 per 100,000 persons.Conclusions:Over 8 seasons, rates of HA influenza were low but were likely underestimated because testing was not systematic. A high proportion of patients with HA influenza were unvaccinated and had severe outcomes. Annual influenza vaccination and implementation of robust hospital infection control measures may help to prevent HA influenza and its impacts on patient outcomes and the healthcare system.

Since SARS-CoV-2, the novel coronavirus that causes coronavirus disease 2019 (COVID-19), was first detected in December 2019 (1), approximately 1.3 million cases have been reported worldwide (2), including approximately 330,000 in the United States (3). To conduct population-based surveillance for laboratory-confirmed COVID-19-associated hospitalizations in the United States, the COVID-19-Associated Hospitalization Surveillance Network (COVID-NET) was created using the existing infrastructure of the Influenza Hospitalization Surveillance Network (FluSurv-NET) (4) and the Respiratory Syncytial Virus Hospitalization Surveillance Network (RSV-NET). This report presents age-stratified COVID-19-associated hospitalization rates for patients admitted during March 1-28, 2020, and clinical data on patients admitted during March 1-30, 2020, the first month of U.S. surveillance. Among 1,482 patients hospitalized with COVID-19, 74.5% were aged ≥50 years, and 54.4% were male. The hospitalization rate among patients identified through COVID-NET during this 4-week period was 4.6 per 100,000 population. Rates were highest (13.8) among adults aged ≥65 years. Among 178 (12%) adult patients with data on underlying conditions as of March 30, 2020, 89.3% had one or more underlying conditions; the most common were hypertension (49.7%), obesity (48.3%), chronic lung disease (34.6%), diabetes mellitus (28.3%), and cardiovascular disease (27.8%). These findings suggest that older adults have elevated rates of COVID-19-associated hospitalization and the majority of persons hospitalized with COVID-19 have underlying medical conditions. These findings underscore the importance of preventive measures (e.g., social distancing, respiratory hygiene, and wearing face coverings in public settings where social distancing measures are difficult to maintain)† to protect older adults and persons with underlying medical conditions, as well as the general public. In addition, older adults and persons with serious underlying medical conditions should avoid contact with persons who are ill and immediately contact their health care provider(s) if they have symptoms consistent with COVID-19 (https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/symptoms.html) (5). Ongoing monitoring of hospitalization rates, clinical characteristics, and outcomes of hospitalized patients will be important to better understand the evolving epidemiology of COVID-19 in the United States and the clinical spectrum of disease, and to help guide planning and prioritization of health care system resources.

Background Recent population-based data are limited regarding influenza-associated hospitalizations in US children. Methods We identified children Results Over 9 seasons, adjusted influenza-associated hospitalization incidence rates ranged from 10 to 375 per 100 000 persons each season and were highest among infants Conclusions Hospitalization and death rates were greatest in younger children at the population level. Among hospitalized children, however, older children had a higher risk of severe outcomes. Continued efforts to prevent and attenuate influenza in children are needed.

Objectives: Supplemental federal funding is allocated to state and local tuberculosis (TB) programs using a formula that considers only countable cases reported to the National Tuberculosis Surveillance System (NTSS). Health departments submit reports of cases, which are countable unless another (US or international) jurisdiction has already counted the case or the case represents a recurrence of TB diagnosed ≤12 months after completion of treatment for a previous TB episode. Noncountable cases are a resource burden, so in 2009, NTSS began accepting noncountable case reports as an indicator of program burden. We sought to describe the volume and completeness of noncountable case reports. Methods: We analyzed 2010-2014 NTSS data to determine the number and distribution of noncountable cases reported. We also surveyed jurisdictions to determine the completeness of noncountable case reporting and obtain information on jurisdictions’ experience in reporting noncountable cases. In addition, we prepared a hypothetical recalculation of the funding formula to evaluate the effect of including noncountable cases on funding allocations. Results: Of 54 067 TB case reports analyzed, 1720 (3.2%) were noncountable; 47 of 60 (78.3%) jurisdictions reported ≥1 noncountable case. Of 60 programs surveyed, 34 (56.7%) responded. Of the 34 programs that responded, 24 (70.6%) had not reported all their noncountable cases to NTSS, and 11 (32.4%) stated that reporting noncountable cases was overly burdensome, considering the cases were not funded. Conclusions: Complete data on noncountable TB cases help support estimates of programmatic burden. Ongoing training and a streamlined reporting system to NTSS can facilitate noncountable case reporting.

Background Hospitalized immunocompromised (IC) adults with influenza may have worse outcomes than hospitalized non-IC adults. Methods We identified adults hospitalized with laboratory-confirmed influenza during 2011–2015 seasons through CDC’s Influenza Hospitalization Surveillance Network. IC patients had human immunodefiency virus (HIV)/AIDS, cancer, stem cell or organ transplantation, nonsteroid immunosuppressive therapy, immunoglobulin deficiency, asplenia, and/or other rare conditions. We compared demographic and clinical characteristics of IC and non-IC adults using descriptive statistics. Multivariable logistic regression and Cox proportional hazards models controlled for confounding by patient demographic characteristics, pre-existing medical conditions, influenza vaccination, and other factors. Results Among 35 348 adults, 3633 (10%) were IC; cancer (44%), nonsteroid immunosuppressive therapy (44%), and HIV (18%) were most common. IC patients were more likely than non-IC patients to have received influenza vaccination (53% vs 46%; P < .001), and ~85% of both groups received antivirals. In multivariable analysis, IC adults had higher mortality (adjusted odds ratio [aOR], 1.46; 95% confidence interval [CI], 1.20–1.76). Intensive care was more likely among IC patients 65–79 years (aOR, 1.25; 95% CI, 1.06–1.48) and those >80 years (aOR, 1.35; 95% CI, 1.06–1.73) compared with non-IC patients in those age groups. IC patients were hospitalized longer (adjusted hazard ratio of discharge, 0.86; 95% CI, .83–.88) and more likely to require mechanical ventilation (aOR, 1.19; 95% CI, 1.05–1.36). Conclusions Substantial morbidity and mortality occurred among IC adults hospitalized with influenza. Influenza vaccination and antiviral administration could be increased in both IC and non-IC adults.

Background The evolution of influenza A viruses results in birth cohorts that have different initial influenza virus exposures. Historically, A/H3 predominant seasons have been associated with more severe influenza-associated disease; however, since the 2009 pandemic, there are suggestions that some birth cohorts experience more severe illness in A/H1 predominant seasons. Methods United States influenza virologic, hospitalization, and mortality surveillance data during 2000–2017 were analyzed for cohorts born between 1918 and 1989 that likely had different initial influenza virus exposures based on viruses circulating during early childhood. Relative risk/rate during H3 compared with H1 predominant seasons during prepandemic versus pandemic and later periods were calculated for each cohort. Results During the prepandemic period, all cohorts had more influenza-associated disease during H3 predominant seasons than H1 predominant seasons. During the pandemic and later period, 4 cohorts had higher hospitalization and mortality rates during H1 predominant seasons than H3 predominant seasons. Conclusions Birth cohort differences in risk of influenza-associated disease by influenza A virus subtype can be seen in US influenza surveillance data and differ between prepandemic and pandemic and later periods. As the population ages, the amount of influenza-associated disease may be greater in future H1 predominant seasons than H3 predominant seasons.

Key Points Question Are rates of severe influenza disease associated with race and ethnicity? Findings In this cross-sectional study of influenza-associated outcomes among 113 352 patients hospitalized with influenza over the course of 10 influenza seasons, Black, Hispanic, and American Indian or Alaska Natives persons had higher rates of hospitalization and intensive care unit admission, even after adjusting for age. The greatest disparities were found in the youngest age groups. Meaning These findings suggest that targeted prevention and intervention efforts, such as improved influenza vaccine coverage and early use of antiviral treatment, could improve influenza-associated outcomes among racial and ethnic minority groups identified in this study as having higher rates of severe influenza disease., This cross-sectional study examines rates of influenza-associated hospitalization, intensive care unit (ICU) admission, and in-hospital death by race and ethnicity in the US from 2009 to 2019., Importance Racial and ethnic minority groups, such as Black, Hispanic, American Indian or Alaska Native, and Asian or Pacific Islander persons, often experience higher rates of severe influenza disease. Objective To describe rates of influenza-associated hospitalization, intensive care unit (ICU) admission, and in-hospital death by race and ethnicity over 10 influenza seasons. Design, Setting, and Participants This cross-sectional study used data from the Influenza-Associated Hospitalization Surveillance Network (FluSurv-NET), which conducts population-based surveillance for laboratory-confirmed influenza-associated hospitalizations in selected counties, representing approximately 9% of the US population. Influenza hospitalizations from the 2009 to 2010 season to the 2018 to 2019 season were analyzed. Data were analyzed from October 2020 to July 2021. Main Outcomes and Measures The main outcomes were age-adjusted and age-stratified rates of influenza-associated hospitalization, ICU admission, and in-hospital death by race and ethnicity overall and by influenza season. Results Among 113 352 persons with an influenza-associated hospitalization (34 436 persons [32.0%] aged ≥75 years; 61 009 [53.8%] women), 70 225 persons (62.3%) were non-Hispanic White (White), 24 850 persons (21.6%) were non-Hispanic Black (Black), 11 903 persons (10.3%) were Hispanic, 5517 persons (5.1%) were non-Hispanic Asian or Pacific Islander, and 857 persons (0.7%) were non-Hispanic American Indian or Alaska Native. Among persons aged younger than 75 years and compared with White persons of the same ages, Black persons were more likely to be hospitalized (eg, age 50-64 years: rate ratio [RR], 2.50 95% CI, 2.43-2.57) and to be admitted to an ICU (eg, age 50-64 years: RR, 2.09; 95% CI, 1.96-2.23). Among persons aged younger than 50 years and compared with White persons of the same ages, American Indian or Alaska Native persons were more likely to be hospitalized (eg, age 18-49 years: RR, 1.72; 95% CI, 1.51-1.96) and to be admitted to an ICU (eg, age 18-49 years: RR, 1.84; 95% CI, 1.40-2.42). Among children aged 4 years or younger and compared with White children, hospitalization rates were higher in Black children (RR, 2.21; 95% CI, 2.10-2.33), Hispanic children (RR, 1.87; 95% CI, 1.77-1.97), American Indian or Alaska Native children (RR, 3.00; 95% CI, 2.55-3.53), and Asian or Pacific Islander children (RR, 1.26; 95% CI, 1.16-1.38), as were rates of ICU admission (Black children: RR, 2.74; 95% CI, 2.43-3.09; Hispanic children: RR, 1.96; 95% CI, 1.73-2.23; American Indian and Alaska Native children: RR, 3.51; 95% CI, 2.45-5.05). In this age group and compared with White children, in-hospital death rates were higher among Hispanic children (RR, 2.98; 95% CI, 1.23-7.19), Black children (RR, 3.39; 95% CI, 1.40-8.18), and Asian or Pacific Islander children (RR, 4.35; 95% CI, 1.55-12.22). Few differences were observed in rates of severe influenza-associated outcomes by race and ethnicity among adults aged 75 years or older. For example, in this age group, compared with White adults, hospitalization rates were slightly higher only among Black adults (RR, 1.05; 95% CI 1.02-1.09). Overall, Black persons had the highest age-adjusted hospitalization rate (68.8 [95% CI, 68.0-69.7] hospitalizations per 100 000 population) and ICU admission rate (11.6 [95% CI, 11.2-11.9] admissions per 100 000 population). Conclusions and Relevance This cross-sectional study found racial and ethnic disparities in rates of severe influenza-associated disease. These data identified subgroups for whom improvements in influenza prevention efforts could be targeted.

Author(s): Kim, Lindsay; Garg, Shikha; O'Halloran, Alissa; Whitaker, Michael; Pham, Huong; Anderson, Evan J; Armistead, Isaac; Bennett, Nancy M; Billing, Laurie; Como-Sabetti, Kathryn; Hill, Mary; Kim, Sue; Monroe, Maya L; Muse, Alison; Reingold, Arthur L; Schaffner, William; Sutton, Melissa; Talbot, H Keipp; Torres, Salina M; Yousey-Hindes, Kimberly; Holstein, Rachel; Cummings, Charisse; Brammer, Lynnette; Hall, Aron J; Fry, Alicia M; Langley, Gayle E | Abstract: BackgroundCurrently, the United States has the largest number of reported coronavirus disease 2019 (COVID-19) cases and deaths globally. Using a geographically diverse surveillance network, we describe risk factors for severe outcomes among adults hospitalized with COVID-19.MethodsWe analyzed data from 2491 adults hospitalized with laboratory-confirmed COVID-19 between 1 March-2 May 2020, as identified through the Coronavirus Disease 2019-Associated Hospitalization Surveillance Network, which comprises 154 acute-care hospitals in 74 counties in 13 states. We used multivariable analyses to assess associations between age, sex, race and ethnicity, and underlying conditions with intensive care unit (ICU) admission and in-hospital mortality.ResultsThe data show that 92% of patients had ≥1 underlying condition; 32% required ICU admission; 19% required invasive mechanical ventilation; and 17% died. Independent factors associated with ICU admission included ages 50-64, 65-74, 75-84, and ≥85 years versus 18-39 years (adjusted risk ratios [aRRs], 1.53, 1.65, 1.84, and 1.43, respectively); male sex (aRR, 1.34); obesity (aRR, 1.31); immunosuppression (aRR, 1.29); and diabetes (aRR, 1.13). Independent factors associated with in-hospital mortality included ages 50-64, 65-74, 75-84, and ≥ 85 years versus 18-39 years (aRRs, 3.11, 5.77, 7.67, and 10.98, respectively); male sex (aRR, 1.30); immunosuppression (aRR, 1.39); renal disease (aRR, 1.33); chronic lung disease (aRR 1.31); cardiovascular disease (aRR, 1.28); neurologic disorders (aRR, 1.25); and diabetes (aRR, 1.19).ConclusionsIn-hospital mortality increased markedly with increasing age. Aggressive implementation of prevention strategies, including social distancing and rigorous hand hygiene, may benefit the population as a whole, as well as those at highest risk for COVID-19-related complications.

CDC collects, compiles, and analyzes data on influenza activity and viruses in the United States. During September 30, 2018-February 2, 2019,* influenza activity† in the United States was low during October and November, increased in late December, and remained elevated through early February. As of February 2, 2019, this has been a low-severity influenza season (1), with a lower percentage of outpatient visits for influenza-like illness (ILI), lower rates of hospitalization, and fewer deaths attributed to pneumonia and influenza, compared with recent seasons. Influenza-associated hospitalization rates among children are similar to those observed in influenza A(H1N1)pdm09 predominant seasons; 28 influenza-associated pediatric deaths occurring during the 2018-19 season have been reported to CDC. Whereas influenza A(H1N1)pdm09 viruses predominated in most areas of the country, influenza A(H3N2) viruses have predominated in the southeastern United States, and in recent weeks accounted for a growing proportion of influenza viruses detected in several other regions. Small numbers of influenza B viruses (

Background As of May 15, 2020, the United States has reported the greatest number of coronavirus disease 2019 (COVID-19) cases and deaths globally. Objective To describe risk factors for severe outcomes among adults hospitalized with COVID-19. Design Cohort study of patients identified through the Coronavirus Disease 2019-Associated Hospitalization Surveillance Network. Setting 154 acute care hospitals in 74 counties in 13 states. Patients 2491 patients hospitalized with laboratory-confirmed COVID-19 during March 1-May 2, 2020. Measurements Age, sex, race/ethnicity, and underlying medical conditions. Results Ninety-two percent of patients had ≥1 underlying condition; 32% required intensive care unit (ICU) admission; 19% invasive mechanical ventilation; 15% vasopressors; and 17% died during hospitalization. Independent factors associated with ICU admission included ages 50-64, 65-74, 75-84 and ≥85 years versus 18-39 years (adjusted risk ratio (aRR) 1.53, 1.65, 1.84 and 1.43, respectively); male sex (aRR 1.34); obesity (aRR 1.31); immunosuppression (aRR 1.29); and diabetes (aRR 1.13). Independent factors associated with in-hospital mortality included ages 50-64, 65-74, 75-84 and ≥85 years versus 18-39 years (aRR 3.11, 5.77, 7.67 and 10.98, respectively); male sex (aRR 1.30); immunosuppression (aRR 1.39); renal disease (aRR 1.33); chronic lung disease (aRR 1.31); cardiovascular disease (aRR 1.28); neurologic disorders (aRR 1.25); and diabetes (aRR 1.19). Race/ethnicity was not associated with either ICU admission or death. Limitation Data were limited to patients who were discharged or died in-hospital and had complete chart abstractions; patients who were still hospitalized or did not have accessible medical records were excluded. Conclusion In-hospital mortality for COVID-19 increased markedly with increasing age. These data help to characterize persons at highest risk for severe COVID-19-associated outcomes and define target groups for prevention and treatment strategies. Funding Source This work was supported by grant CK17-1701 from the Centers of Disease Control and Prevention through an Emerging Infections Program cooperative agreement and by Cooperative Agreement Number NU38OT000297-02-00 awarded to the Council of State and Territorial Epidemiologists from the Centers for Disease Control and Prevention.

The United States 2017-18 influenza season (October 1, 2017-May 19, 2018) was a high severity season with high levels of outpatient clinic and emergency department visits for influenza-like illness (ILI), high influenza-related hospitalization rates, and elevated and geographically widespread influenza activity across the country for an extended period. Nationally, ILI activity began increasing in November, reaching an extended period of high activity during January-February, and remaining elevated through March. Influenza A(H3N2) viruses predominated through February and were predominant overall for the season; influenza B viruses predominated from March onward. This report summarizes U.S. influenza activity* during October 1, 2017-May 19, 2018.†.

Influenza activity in the United States was low during October 2017, but has been increasing since the beginning of November. Influenza A viruses have been most commonly identified, with influenza A(H3N2) viruses predominating. Several influenza activity indicators were higher than is typically seen for this time of year. The majority of influenza viruses characterized during this period were genetically or antigenically similar to the 2017-18 Northern Hemisphere cell-grown vaccine reference viruses. These data indicate that currently circulating viruses have not undergone significant antigenic drift; however, circulating A(H3N2) viruses are antigenically less similar to egg-grown A(H3N2) viruses used for producing the majority of influenza vaccines in the United States. It is difficult to predict which influenza viruses will predominate in the 2017-18 influenza season; however, in recent past seasons in which A(H3N2) viruses predominated, hospitalizations and deaths were more common, and the effectiveness of the vaccine was lower. Annual influenza vaccination is recommended for all persons aged ≥6 months who do not have contraindications. Multiple influenza vaccines are approved and recommended for use during the 2017-18 season, and vaccination should continue to be offered as long as influenza viruses are circulating and unexpired vaccine is available. This report summarizes U.S. influenza activity* during October 1-November 25, 2017 (surveillance weeks 40-47).†.

Background Influenza hospitalizations result in substantial morbidity and mortality each year. Little is known about the association between influenza hospitalization and census tract‐based socioeconomic determinants beyond the effect of individual factors. Objective To evaluate whether census tract‐based determinants such as poverty and household crowding would contribute significantly to the risk of influenza hospitalization above and beyond individual‐level determinants. Methods We analyzed 33 515 laboratory‐confirmed influenza‐associated hospitalizations that occurred during the 2009‐2010 through 2013‐2014 influenza seasons using a population‐based surveillance system at 14 sites across the United States. Results Using a multilevel regression model, we found that individual factors were associated with influenza hospitalization with the highest adjusted odds ratio (AOR) of 9.20 (95% CI 8.72‐9.70) for those ≥65 vs 5‐17 years old. African Americans had an AOR of 1.67 (95% CI 1.60‐1.73) compared to Whites, and Hispanics had an AOR of 1.21 (95% CI 1.16‐1.26) compared to non‐Hispanics. Among census tract‐based determinants, those living in a tract with ≥20% vs

During the 2016-17 influenza season (October 2, 2016-May 20, 2017) in the United States, influenza activity* was moderate. Activity remained low through November, increased during December, and peaked in February nationally, although there were regional differences in the timing of influenza activity. Influenza A(H3N2) viruses predominated through mid-March and were predominant overall for the season, but influenza B viruses were most commonly reported from late March through May. This report summarizes influenza activity in the United States during October 2, 2016-May 20, 2017† and updates the previous summary (1).

Background Significant changes in influenza vaccination coverage and antiviral treatment guidance occurred following the 2009 influenza pandemic in children. However, data are limited describing recent epidemiology, clinical characteristics, antiviral use, vaccine coverage, and outcomes of influenza-related hospitalizations in children. Methods Children < 18 years hospitalized with influenza during seasons 2010–2011 through 2018–2019 were included through the US Influenza Hospitalization Surveillance Network (FluSurv-NET). Age-stratified hospitalization rates were calculated using the number of catchment-area residents with laboratory-confirmed influenza within 14 days prior to or ≤3 days after hospital admission during October 1-April 30 of each influenza season. Data on underlying medical history, influenza vaccination, antiviral use, and outcomes were abstracted from medical records using standard case report forms by trained surveillance officers. Results Over 9 seasons, 13,235 children were identified. Stepwise decreases in unadjusted hospitalization rates with age occurred, with the highest rates in infants < 6 months (ranging 56–184 per 100,000 persons) (Fig.1). Among these children, 56% were male, 34% were non-Hispanic White, 55% had a preexisting medical condition, and 8% were immunocompromised (Table 1). Use of antiviral treatment substantially increased from 56% to 85%, and influenza vaccination rates among hospitalized children increased from 34% to 43% over time. Regarding severe outcomes, 2,676 (20%) were admitted to ICU, 2,262 (17%) had pneumonia, 690 (5%) required mechanical ventilation, and 72 (0.5%) died. In univariable analysis, compared to hospitalized infants < 6 months, children >13 years had higher odds of ICU admission (odds ratio (OR), 2.0; 95% CI, 1.7–2.4), mechanical ventilation (OR, 1.7; 95% CI, 1.2–2.3), and pneumonia (OR, 2.6; 95% CI, 2.1–3.3) (Table 2). Figure 1 Table 1 Table 2 Conclusion Although influenza-related hospitalization rates decreased with increasing age, severe outcomes were more common among hospitalized older children. Room for improvement exists in influenza vaccination coverage and antiviral use. While 20% of children were admitted to ICU, death was uncommon. Disclosures Sue Kim, MPH, Council of State and Territorial Epidemiologists (CSTE) (Grant/Research Support) Melissa Sutton, MD, MPH, CDC funding (Emerging Infections Program) (Grant/Research Support) Evan J. Anderson, MD, Sanofi Pasteur (Scientific Research Study Investigator)

Background Multivalent influenza vaccine products provide protection against influenza A(H1N1)pdm09, A(H3N2), and B lineage viruses. The 2018–2019 influenza season in the United States included prolonged circulation of A(H1N1)pdm09 viruses well-matched to the vaccine strain and A(H3N2) viruses, the majority of which were mismatched to the vaccine. We estimated the number of vaccine-prevented influenza-associated illnesses, medical visits, hospitalizations, and deaths for the season. Methods We used a mathematical model and Monte Carlo algorithm to estimate numbers and 95% uncertainty intervals (UIs) of influenza-associated outcomes prevented by vaccination in the United States. The model incorporated age-specific estimates of national 2018–2019 influenza vaccine coverage, influenza virus–specific vaccine effectiveness from the US Influenza Vaccine Effectiveness Network, and disease burden estimated from population-based rates of influenza-associated hospitalizations through the Influenza Hospitalization Surveillance Network. Results Influenza vaccination prevented an estimated 4.4 million (95%UI, 3.4 million–7.1 million) illnesses, 2.3 million (95%UI, 1.8 million–3.8 million) medical visits, 58 000 (95%UI, 30 000–156 000) hospitalizations, and 3500 (95%UI, 1000–13 000) deaths due to influenza viruses during the US 2018–2019 influenza season. Vaccination prevented 14% of projected hospitalizations associated with A(H1N1)pdm09 overall and 43% among children aged 6 months–4 years. Conclusions Influenza vaccination averted substantial influenza-associated disease including hospitalizations and deaths in the United States, primarily due to effectiveness against A(H1N1)pdm09. Our findings underscore the value of influenza vaccination, highlighting that vaccines measurably decrease illness and associated healthcare utilization even in a season in which a vaccine component does not match to a circulating virus.

Influenza activity* in the United States during the 2018-19 season (September 30, 2018-May 18, 2019) was of moderate severity (1). Nationally, influenza-like illness (ILI)† activity began increasing in November, peaked during mid-February, and returned to below baseline in mid-April; the season lasted 21 weeks,§ making it the longest season in 10 years. Illness attributed to influenza A viruses predominated, with very little influenza B activity. Two waves of influenza A were notable during this extended season: influenza A(H1N1)pdm09 viruses from October 2018 to mid-February 2019 and influenza A(H3N2) viruses from February through May 2019. Compared with the 2017-18 influenza season, rates of hospitalization this season were lower for adults, but were similar for children. Although influenza activity is currently below surveillance baselines, testing for seasonal influenza viruses and monitoring for novel influenza A virus infections should continue year-round. Receiving a seasonal influenza vaccine each year remains the best way to protect against seasonal influenza and its potentially severe consequences.

BackgroundRates of influenza hospitalizations differ by age, but few data are available regarding differences in laboratory-confirmed rates among adults aged ≥65 years.MethodsWe evaluated age-related differences in influenza-associated hospitalization rates, clinical presentation, and outcomes among 19 760 older adults with laboratory-confirmed influenza at 14 FluSurv-NET sites during the 2011–2012 through 2014–2015 influenza seasons using 10-year age groups.ResultsThere were large stepwise increases in the population rates of influenza hospitalization with each 10-year increase in age. Rates ranged from 101–417, 209–1264, and 562–2651 per 100 000 persons over 4 influenza seasons in patients aged 65–74 years, 75–84 years, and ≥85 years, respectively. Hospitalization rates among adults aged 75–84 years and ≥85 years were 1.4–3.0 and 2.2–6.4 times greater, respectively, than rates for adults aged 65–74 years. Among patients hospitalized with laboratory-confirmed influenza, there were age-related differences in demographics, medical histories, and symptoms and signs at presentation. Compared to hospitalized patients aged 65–74 years, patients aged ≥85 years had higher odds of pneumonia (aOR, 1.2; 95% CI, 1.0–1.3; P = .01) and in-hospital death or transfer to hospice (aOR, 2.1; 95% CI, 1.7–2.6; P < .01).ConclusionsAge-related differences in the incidence and severity of influenza hospitalizations among adults aged ≥65 years can inform prevention and treatment efforts, and data should be analyzed and reported using additional age strata.

Influenza activity in the United States was low during October 2018, and, although it increased slowly during November, activity remains low across most of the country.* During the week ending December 1, 2018, the percentage of outpatient visits for influenza-like illness† (ILI) was equal to the national baseline§ (Figure) and was at or slightly above the region-specific baseline in four of the 10 U.S. Department of Health and Human Services regions¶ (Regions 4 and 7–9). The majority of jurisdictions experienced minimal or low ILI activity since September 30; however, two experienced moderate ILI activity, and two experienced high ILI activity** during the week ending December 1. The percentage of deaths attributed to pneumonia and influenza remains below the epidemic threshold,†† and the rate of influenza-associated hospitalizations remains low. Five laboratory-confirmed, influenza-associated pediatric deaths occurring since September 30 have been reported to CDC. During the week ending December 1, the majority of jurisdictions (40 states, the District of Columbia, Puerto Rico, and U.S. Virgin Islands) reported sporadic or local geographic spread of influenza activity, nine states reported regional activity, and one state reported widespread activity.§§ Open in a separate window FIGURE Percentage of visits for influenza-like illness (ILI) — U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet), weekly national summary, 2018–2019* and selected previous seasons * As of December 7, 2018.

Background Existing data on the clinical features and outcomes of immunocompromised children with influenza are limited. Methods Data from the 2011–2012 through 2014–2015 influenza seasons were collected as part of the Centers for Disease Control and Prevention (CDC) Influenza Hospitalization Surveillance Network (FluSurv-NET). We compared clinical features and outcomes between immunocompromised and nonimmunocompromised children ( Results Among 5262 hospitalized children, 242 (4.6%) were immunocompromised; receipt of nonsteroidal immunosuppressive therapy (60%), cancer (39%), and solid organ transplantation (14%) were most common. Immunocompromised children were older than the nonimmunocompromised children (median, 8.8 vs 2.8 years, respectively; P < .001), more likely to have another comorbidity (58% vs 49%, respectively; P = .007), and more likely to have received an influenza vaccination (58% vs 39%, respectively; P < .001) and early antiviral treatment (35% vs 27%, respectively; P = .013). In multivariable analyses, immunocompromised children were less likely to receive intensive care (adjusted odds ratio [95% confidence interval], 0.31 [0.20–0.49]) and had a slightly longer duration of hospitalization (adjusted hazard ratio of hospital discharge [95% confidence interval], 0.89 [0.80–0.99]). Death was uncommon in both groups. Conclusions Immunocompromised children hospitalized with influenza received intensive care less frequently but had a longer hospitalization duration than nonimmunocompromised children. Vaccination and early antiviral use could be improved substantially. Data are needed to determine whether immunocompromised children are more commonly admitted with milder influenza severity than are nonimmunocompromised children.

Background The 2018–19 influenza season was characterized by prolonged co-circulation of Influenza A H3N2 (H3) and H1N1pdm09 (H1) viruses. We used data from the Influenza Hospitalization Surveillance Network (FluSurv-NET) to describe age-related differences in the distribution of influenza A subtypes. Methods We included all cases residing within a FluSurv-NET catchment area and hospitalized with laboratory-confirmed influenza during October 1, 2018–April 30, 2019. We multiply imputed influenza A subtype for 63% of cases with unknown subtype and based imputation on factors that could be associated with missing subtype including surveillance site, 10-year age groups and month of hospital admission. We calculated influenza hospitalization rates and 95% confidence intervals (95% CI) by type and subtype per 100,000 population. We compared the proportion of cases with H1 by year of age in FluSurv-NET to the distribution obtained from US public health laboratories participating in virologic surveillance and providing specimen-level influenza Results. Results Based on available data, 18,669 hospitalizations were reported; 41% received influenza vaccination ≥2 weeks prior to hospitalization and 90% received antivirals. Cumulative hospitalization rates per 100,000 population were as follows: H1 32.5 (95% CI 31.7–33.3), H3 29.3 (95% CI 28.5–30.1) and B 2.5 (95% CI 2.3–2.7). Based on weekly rates, H1 hospitalizations peaked during February (week 8) and H3 hospitalizations during March (week 11) (Figure A). FluSurv-NET data showed distinct patterns of subtype distribution by age, with H1 predominating among cases 0–9 and 24–70 years, and H3 predominating among cases 10–23 and ≥71 years. Data on the proportion of H1 results by age correlated well between FluSurv-NET and US virologic surveillance (Figure B). Conclusion Influenza A H1 and H3 virus circulation patterns varied by age group during the 2018–2019 season. The proportion of cases with H1 relative to H3 was low among those born between 1996 and 2009 and those born before 1948. These findings may indicate protection against H1 viruses in age groups with exposure to H1N1pdm09 during the 2009 pandemic or to older antigenically similar H1N1 viruses as young children. Disclosures Evan J. Anderson, MD, AbbVie (Consultant), GSK (Grant/Research Support), Merck (Grant/Research Support), Micron (Grant/Research Support), PaxVax (Grant/Research Support), Pfizer (Consultant, Grant/Research Support), sanofi pasteur (Grant/Research Support), Keipp Talbot, MD, MPH, Sequirus (Other Financial or Material Support, On Data Safety Monitoring Board).

Background Seasonal influenza vaccine may attenuate disease severity among people infected with influenza despite vaccination, but vaccine effectiveness may decrease with increasing time between vaccination and infection. Patient characteristics may play a role in the timing of vaccine receipt. Methods We used data from the Influenza Hospitalization Surveillance Network (FluSurv-NET) and included patients ≥ 9 years hospitalized with laboratory-confirmed influenza during October 1–April 30 of influenza seasons 2013–2014 through 2016–2017 who received seasonal influenza vaccine ≥ 14 days prior to admission. Vaccine history was obtained from vaccine registries, medical charts, and patient interviews. We defined “early vaccination” as vaccine receipt before October 15 and “late vaccination” as receipt after (date selected using typical season onset and median vaccination dates). Early and late groups were compared using Chi-square or Fisher exact tests. Results Among 21,751 vaccinated patients, 61% received vaccine before October 15, and distribution of vaccination date was similar across seasons (figure). Vaccination occurred earlier with increasing age (45% were vaccinated early among those 9–17 years but 65% in those ≥ 80 years, P < 0.01). White non-Hispanic patients were more likely to receive vaccine early compared with black non-Hispanic and Hispanic patients (63% vs. 55% and 54%; P < 0.01). Those with metabolic disorders, cardiovascular disease, kidney disease, and cancer were vaccinated earlier whereas those with HIV and liver disease were vaccinated later. Vaccine timing also varied by state (P < 0.01) but not by sex. Conclusion Among influenza-vaccinated older children and adults hospitalized with influenza, older age, white race, and certain medical conditions were associated with early receipt of influenza vaccination in unadjusted analysis. This may be due to frequent healthcare encounters and targeted public health strategies in high-risk groups. Understanding how timing of vaccine receipt varies among populations can provide insights into variables that must be controlled for in studying possible vaccine effectiveness waning and attenuation of disease among those who are infected despite vaccination. Disclosures All authors: No reported disclosures.

From October through mid-December 2015, influenza activity remained low in most regions of the United States. Activity began to increase in late December 2015 and continued to increase slowly through early February 2016. Influenza A viruses have been most frequently identified, with influenza A (H3N2) viruses predominating during October until early December, and influenza A (H1N1)pdm09 viruses predominating from mid-December until early February. Most of the influenza viruses characterized during that time are antigenically similar to vaccine virus strains recommended for inclusion in the 2015-16 Northern Hemisphere vaccines. This report summarizes U.S. influenza activity* during October 4, 2015-February 6, 2016, and updates the previous summary (1).

Background Influenza B viruses (B) co-circulate with influenza A viruses (A) and contribute to influenza-associated hospitalizations each season. We used data from the Influenza Hospitalization Surveillance Network (FluSurv-NET) to determine the association between B virus hospitalizations and mortality among children. Methods We included data from children aged 0–17 years, residing in a FluSurv-NET catchment area, and hospitalized with laboratory-confirmed influenza during 2011–2012 through 2016–2017. We abstracted data on underlying conditions, clinical course and outcomes from medical charts. After excluding cases with unknown influenza type or with A/B coinfection, we compared characteristics of children hospitalized with A vs. B using univariate analyses and multivariable logistic regression, to determine the independent association between virus type and in-hospital mortality. Results Among 7671 children hospitalized with influenza, 5607 (73%) had A and 2064 (27%) had B. The proportion of B hospitalizations varied by season from 11% during 2013–2014 to 42% during 2012–2013. Among children with B, median age was 4 years (interquartile range 1–8 years), 58% were male and 36% were non-Hispanic white. In univariate analysis, children with B were more likely to be older, have cardiovascular and neurologic disease, to be vaccinated (38 vs. 32%), and to be hospitalized ≥2 days after illness onset, and were less likely to have asthma and receive antivirals (71 vs. 79%) compared with those with A (P < 0.05). There were no differences in the proportion with ≥1 underlying condition (59% both groups). Patients with B vs. A were no more likely to require intensive care (19 vs. 20%; p 0.34) or receive mechanical ventilation (6 vs. 5%; p 0.13); however, patients with B were more likely to die in-hospital (1 vs. 0.4%; P < 0.01). The unadjusted odds of in-hospital mortality for children with B vs. A was 2.3 (95% confidence interval (CI) 1.3–4.1), which remained elevated at 2.0 (95% CI 1.1–3.7) after adjusting for age, season and underlying conditions. Conclusion Influenza B virus infections were associated with severe outcomes among hospitalized children. Although death was uncommon, children with B had twice the odds of dying in-hospital compared with those with A virus infection. Disclosures E. J. Anderson, NovaVax: Grant Investigator, Research grant. Pfizer: Grant Investigator, Research grant. AbbVie: Consultant, Consulting fee. MedImmune: Investigator, Research support. PaxVax: Investigator, Research support. Micron: Investigator, Research support. H. K. Talbot, Sanofi Pasteur: Investigator, Research grant. Gilead: Investigator, Research grant. MedImmune: Investigator, Research grant. Vaxinnate: Safety Board, none. Seqirus: Safety Board, none.

Background Influenza is most commonly associated with respiratory complications; however, nonrespiratory complications occur frequently among patients hospitalized with influenza. We used data from the Influenza Hospitalization Surveillance Network (FluSurv-NET) to describe complications recorded on discharge summaries of patients hospitalized with influenza. Methods We included children (0–17 years) and adults (≥18 years), who resided within a FluSurv-NET catchment area and were hospitalized with laboratory-confirmed influenza during 2016–2017. We abstracted data on underlying conditions and discharge diagnoses from medical charts. We calculated the frequency of respiratory and nonrespiratory complications in all age groups and used univariate and multivariable logistic regression to examine factors associated with select complications among adults. Results Among 17,489 patients, the most common respiratory complications were pneumonia (26%) and acute respiratory failure (23%) and the most common nonrespiratory complications were sepsis (16%) and acute renal failure (ARF) (12%). Complications varied by age group (figure). Pneumonia was the most common respiratory complication in all age groups except 0–4 years; among children aged 0–4 years bronchiolitis was most common (104/712; 15%). Among 97 children aged 0–4 years with bronchiolitis who underwent testing for respiratory syncytial virus (RSV), 37% had RSV. The most common nonrespiratory complication was seizures in children aged 0–17 years (17% had a history of prior seizures) and sepsis in adults. Among adults (n = 16,057), factors most strongly associated with ARF included chronic renal disease (adjusted odds ratio (AOR) 2.5; 95% confidence interval (95% CI) 2.2–2.8), male sex (AOR 1.5 95% CI 1.4–1.7) and age ≥65 years (AOR 1.4 95% CI 1.2–1.7); the factor most strongly associated with sepsis was chronic neuromuscular disease (AOR 1.5 95% CI 1.3–1.8). Conclusion Influenza hospitalizations are associated with a broad spectrum of complications including pneumonia, respiratory failure, sepsis, ARF and seizures. During the influenza season, astute clinicians should keep influenza in the differential diagnosis for patients with a wide range of presentations. :Disclosures. H. K. Talbot, sanofi pasteur: Investigator, Research grant. Gilead: Investigator, Research grant. MedImmune: Investigator, Research grant. Vaxinnate: Safety Board, none. Seqirus: Safety Board, none. E. J. Anderson, NovaVax: Grant Investigator, Research grant. Pfizer: Grant Investigator, Research grant. AbbVie: Consultant, Consulting fee. MedImmune: Investigator, Research support. PaxVax: Investigator, Research support. Micron: Investigator, Research support.

Background Influenza vaccination may reduce illness severity among those with influenza; however, data are limited. We determined whether outcomes were less severe among vaccinated compared with unvaccinated adults hospitalized with influenza over 5 seasons. Methods We included adults (≥18 years) hospitalized with laboratory-confirmed influenza during seasons 2013–2014 through 2017–2018 and identified through the US Influenza Hospitalization Surveillance Network (FluSurv-NET). Vaccination status was obtained through medical records, vaccine registries, and interviews. We excluded patients who were institutionalized, did not receive antivirals, or had unknown vaccine status or vaccine receipt Results Among 67,452 adults hospitalized with influenza, 43,608 were included; 47% were 18–64 years (38% vaccinated) and 53% were ≥65 years (65% vaccinated). Among patients with influenza A(H1N1)pdm09, vaccination was associated with decreased odds of ICU admission (odds ratio (OR) 0.81; OR 0.72) and MV (OR 0.66; OR 0.54) in adults 18–64 and ≥65 years, respectively; decreased odds of pneumonia (OR 0.83), death (OR 0.64) and shortened ICU LOS (relative hazard (RH) 0.82) in adults 18–64 years; and shortened hospital LOS (RH 0.91) in adults ≥65 years (figure). Vaccination was not associated with attenuation of severe outcomes in patients with influenza A(H3N2) and B. Conclusion Vaccination was associated with reduced odds of severe outcomes, including death, by up to 36% in adults hospitalized with influenza A(H1N1)pdm09. All adults without contraindications should receive annual influenza vaccination as there is evidence that it can improve outcomes among those who develop influenza despite vaccination. Disclosures All Authors: No reported Disclosures.

This report summarizes U.S. influenza activity* during October 2, 2016-February 4, 2017

This report summarizes U.S. influenza activity* during October 2-December 17, 2016.† Influenza activity in the United States remained low in October and has been slowly increasing since November. Influenza A viruses were identified most frequently, with influenza A (H3N2) viruses predominating. Most influenza viruses characterized during this period were genetically or antigenically similar to the reference viruses representing vaccine components recommended for production in the 2016-17 Northern Hemisphere influenza vaccines.

During the 2015-16 influenza season (October 4, 2015-May 21, 2016) in the United States, influenza activity* was lower and peaked later compared with the previous three seasons (2012-13, 2013-14, and 2014-15). Activity remained low from October 2015 until late December 2015 and peaked in mid-March 2016. During the most recent 18 influenza seasons (including this season), only two other seasons have peaked in March (2011-12 and 2005-06). Overall influenza activity was moderate this season, with a lower percentage of outpatient visits for influenza-like illness (ILI),(†) lower hospitalization rates, and a lower percentage of deaths attributed to pneumonia and influenza (P&I) compared with the preceding three seasons. Influenza A(H1N1)pdm09 viruses predominated overall, but influenza A(H3N2) viruses were more commonly identified from October to early December, and influenza B viruses were more commonly identified from mid-April through mid-May. The majority of viruses characterized this season were antigenically similar to the reference viruses representing the recommended components of the 2015-16 Northern Hemisphere influenza vaccine (1). This report summarizes influenza activity in the United States during the 2015-16 influenza season (October 4, 2015-May 21, 2016)(§) and reports the vaccine virus components recommended for the 2016-17 Northern Hemisphere influenza vaccines.

Background Few data describe the epidemiology of influenza among adults ≥65 years old according to age strata. We evaluated age-related differences in influenza-associated hospitalization rates, clinical presentation, and outcomes among older adults at 14 FluSurv-NET sites during the 2011–2012 through 2014-2015 influenza seasons. Methods Study patients were hospitalized ≤14 days after and ≤3 days before a positive influenza test. Age strata were 65–74, 75–84, and ≥85 years old. We adjusted hospitalization rates for under detection and assessed for age-related trends in risk factors and symptoms. We used logistic regression to calculate odds ratios (OR) for pneumonia and in-hospital death adjusted for season, sex, nursing home residence, smoking, medical comorbidities, influenza vaccination, and study site. Results There were 19,760 patients, including 5,956 aged 65–74 years, 6,998 aged 75–84 years, and 6,806 aged ≥85 years. There was a stepwise increase in hospitalization rates with age (figure). Increasing age was positively associated with female sex, nursing home residence, neurologic disorder, cardiovascular and renal disease, and vaccination, and inversely associated with morbid obesity, smoking, asthma, chronic metabolic disease, and immunosuppression (P < 0.01). Among 10,548 (53.3%) patients with symptom data from 2014 to 2015, increasing age was associated with a higher prevalence of altered mental status and lower prevalence of fever, myalgias, respiratory or gastrointestinal symptoms, and headache (P ≤ 0.01). Compared with 65–74 year olds, older patients had a higher risk of pneumonia (≥85 year-olds: OR 1.2, 95% CI 1.0, 1.3, P = 0.01) and death (75–84 year olds: OR 1.4, 95% CI 1.2, 1.7, P < 0.01; ≥85 year-olds: OR 2.1, 95% CI 1.7, 2.6, P < 0.01). Conclusion There are age-related differences in the epidemiology, clinical presentation, and outcomes of older adults hospitalized with influenza. These may reflect differences in health status and healthcare provider practice patterns. Public health epidemiologists should consider using additional age strata in ≥65 year-olds when analyzing influenza surveillance data. Clinicians should be aware that influenza among the oldest adults may present atypically and that mortality is increased. Disclosures E. J. Anderson, NovaVax: Grant Investigator, Research grant. Pfizer: Grant Investigator, Research grant. AbbVie: Consultant, Consulting fee. MedImmune: Investigator, Research support. PaxVax: Investigator, Research support. Micron: Investigator, Research support. W. Schaffner, Merck: Member, Data Safety Monitoring Board, Consulting fee. Pfizer: Member, Data Safety Monitoring Board, Consulting fee. Dynavax: Consultant, Consulting fee. Seqirus: Consultant, Consulting fee. SutroVax: Consultant, Consulting fee. Shionogi: Consultant, Consulting fee.

Background The 2017–2018 influenza season had the highest rates of influenza hospitalizations since the 2009 H1N1 pandemic. We used data from the Influenza Hospitalization Surveillance Network (FluSurv-NET) to identify unique characteristics of the 2017–2018 season. Methods We included all patients residing within a FluSurv-NET catchment area, and hospitalized with laboratory-confirmed influenza during 2017–2018. We used multiple imputation, including age, surveillance site, and month of hospital admission as predictors, to impute influenza A subtype for 40–64% of cases across seasons with an unknown subtype. We calculated influenza hospitalization rates by type/subtype per 100,000 population. We compared 2017–2018 rates to rates during 4 prior seasons: 2016–2017, 2015–2016, 2014–2015, and 2013–2014. Results The overall unadjusted hospitalization rates per 100,000 population varied from 31.5 during 2015–2016 to 105.1 during 2017–2018. After imputing A subtype, the 2017–2018 season had the highest rates observed for H3N2 (62.8) and B (28.5) than in any previous season, and the third highest rate of H1N1 (13.5) (Figure 1A). During 2017–2018, rates in adult ≥65 years peaked 3 weeks before they peaked in children 0–4 years. In contrast, during the four prior seasons, rates in adults ≥65 years peaked during the same week or 1 week after they peaked in children 0–4 years. During 2017–2018, the distribution of influenza type/subtypes varied significantly by age group (P < 0.0001); for example, the proportion of cases with H1N1 ranged from 19 to 29% in those 25% of A cases across all age groups (except ≥65 years) vs. all prior seasons where the nonpredominant A virus contributed Conclusions Several unique characteristics may have contributed to the high hospitalization rates observed during 2017–2018. Rates in older adults, who were predominantly infected with H3N2, peaked several weeks prior to children in contrast to prior seasons. Higher overall rates of H3N2 and B were observed in 2017–2018 compared with these prior seasons and substantial H1N1 co-circulation also occurred with marked variability by age group. Disclosures E. J. Anderson, NovaVax: Grant Investigator, Research grant. Pfizer: Grant Investigator, Research grant. AbbVie: Consultant, Consulting fee. MedImmune: Investigator, Research support. PaxVax: Investigator, Research support. Micron: Investigator, Research support. H. K. Talbot, Sanofi Pasteur: Investigator, Research grant. Gilead: Investigator, Research grant. MedImmune: Investigator, Research grant. Vaxinnate: Safety Board, none. Seqirus: Safety Board, none.

Background Influenza results in an estimated 12,000–56,000 deaths annually in the USA. While in-hospital deaths are well characterized, less is known about deaths that occur after discharge among those hospitalized with influenza. Methods We identified patients hospitalized with laboratory-confirmed influenza who died during hospitalization or within 30 days after discharge during the 2014–2015 influenza season for 11 Influenza Hospitalization Surveillance Network sites. We matched cases to the National Center for Health Statistics Electronic Death Registration System and abstracted cause and location of death from death certificates. We compared clinical characteristics between those who died during hospitalization and those who died after hospital discharge using χ2 tests. Results Among 795 patients with laboratory-confirmed influenza who died, 370 (47%) died during hospitalization, and 425 (53%) died within 30 days after discharge. Eighteen (2%) were 0–17 years and 652 (82%) were ≥65 years. Common causes of death listed in any position on the death certificate included influenza (35%), other respiratory causes (50%), cardiovascular disease (37%), and sepsis (15%). Among those who died after discharge, 207 (49%) died within 7 days, 86 (20%) within 8–14 days, and 132 (31%) within 15–30 days post discharge. Patients who died after discharge were more likely to be ≥65 years (88 vs. 74%) or admitted from a nursing home (48 vs. 36%), but were less likely to be admitted to an intensive care unit (30 vs. 68%) or receive a pneumonia diagnosis (46 vs. 62%) than patients who died during hospitalization (all P Conclusion Over half of deaths among patients hospitalized with laboratory-confirmed influenza occurred after discharge. Patients who died after discharge were older and less likely to have influenza listed as a cause of death. Deaths that occur after an influenza-related hospitalization represent an important and under-characterized contribution to the burden of seasonal influenza. Disclosures E. J. Anderson, AbbVie: Consultant, Consulting fee; NovaVax: Research Contractor, Research support; Regeneron: Research Contractor, Research grant; MedImmune: Research Contractor, Research grant and Research support. W. Schaffner, Pfizer: Scientific Advisor, Consulting fee; Merck: Scientific Advisor, Consulting fee; Novavax: Consultant, Consulting fee; Dynavax: Consultant, Consulting fee; Sanofi-pasteur: Consultant, Consulting fee; GSK: Consultant, Consulting fee; Seqirus: Consultant, Consulting fee

Background Data on immunocompromised (IC) adults with influenza are limited but suggest they may present differently and have worse outcomes than non-IC adults. Using a national surveillance system, we describe the epidemiology of IC adults hospitalized with influenza. Methods We analyzed data on adults (aged ≥18 years) hospitalized with laboratory-confirmed influenza during the 2011–2012 through 2014–2015 seasons and reported to CDC’s Influenza Hospitalization Surveillance Network (FluSurv-NET). We defined IC patients as having ≥1 of the following: HIV, AIDS, cancer, stem cell or organ transplantation, non-steroid immunosuppressive therapy, immunoglobulin deficiency, asplenia, and other rare conditions. We compared IC and non-IC patients using χ2 or Fisher’s exact tests and t-tests or Mann–Whitney U tests. Results Among 35,348 adults hospitalized over four seasons, 3,633 (10%) were IC. The most common IC conditions were cancer (44%), non-steroid immunosuppressive therapy (44%), and HIV (17%). IC patients were younger than non-IC patients (mean 61 ± 17 vs. 67 ± 20 years; P < 0.01). IC patients were more likely to have underlying renal disease (27% vs. 18%) and liver disease (7% vs. 3%) and less likely to have most other chronic underlying conditions including obesity (18% vs. 23%), cardiovascular disease (40% vs. 47%), and chronic lung disease (35% vs. 41%; P < 0.01 for all). IC patients were more likely to have received influenza vaccination (53% vs. 46%; P < 0.01). Among cases with symptom data (2014–2015), IC patients were more likely to present with fever (68% vs. 61%; P < 0.01) but respiratory distress was similar (53% vs. 54%; P = 0.3). Overall, the majority of IC and non-IC patients received antivirals (87% vs. 85%; P < 0.01). IC patients had a longer duration of hospitalization (median (IQR) 4 (2–6) vs. 3 (2–6) days; P < 0.01) and were more likely to be diagnosed with pneumonia (34 vs. 31%; P < 0.01) and to require intensive care (18% vs. 16%; P = 0.01). Death during hospitalization occurred in 135 (3.7%) IC and 945 (3.0%) non-IC patients (P = 0.01). Conclusion Among adults hospitalized with influenza, IC patients had worse outcomes including a longer duration of hospitalization and higher probability of pneumonia and intensive care unit admission, and increased all-cause mortality, although these results are not adjusted for potential confounders. Disclosures W. Schaffner, Pfizer: Scientific Advisor, Consulting fee. Merck: Scientific Advisor, Consulting fee. Novavax: Consultant, Consulting fee. Dynavax: Consultant, Consulting fee. Sanofi-pasteur: Consultant, Consulting fee. GSK: Consultant, Consulting fee. Seqirus: Consultant, Consulting fee. E. J. Anderson, AbbVie: Consultant, Consulting fee. NovaVax: Research Contractor, Research support. Regeneron: Research Contractor, Research grant. MedImmune: Research Contractor, Research grant and Research support