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Background: Influenza circulation during the 2022-2023 season in the United States largely returned to pre-coronavirus disease 2019 (COVID-19)-pandemic patterns and levels. Influenza A(H3N2) viruses were detected most frequently this season, predominately clade 3C.2a1b.2a, a close antigenic match to the vaccine strain., Methods: To understand effectiveness of the 2022-2023 influenza vaccine against influenza-associated hospitalization, organ failure, and death, a multicenter sentinel surveillance network in the United States prospectively enrolled adults hospitalized with acute respiratory illness between 1 October 2022, and 28 February 2023. Using the test-negative design, vaccine effectiveness (VE) estimates against influenza-associated hospitalization, organ failures, and death were measured by comparing the odds of current-season influenza vaccination in influenza-positive case-patients and influenza-negative, SARS-CoV-2-negative control-patients., Results: A total of 3707 patients, including 714 influenza cases (33% vaccinated) and 2993 influenza- and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-negative controls (49% vaccinated) were analyzed. VE against influenza-associated hospitalization was 37% (95% confidence interval [CI]: 27%-46%) and varied by age (18-64 years: 47% [30%-60%]; ≥65 years: 28% [10%-43%]), and virus (A[H3N2]: 29% [6%-46%], A[H1N1]: 47% [23%-64%]). VE against more severe influenza-associated outcomes included: 41% (29%-50%) against influenza with hypoxemia treated with supplemental oxygen; 65% (56%-72%) against influenza with respiratory, cardiovascular, or renal failure treated with organ support; and 66% (40%-81%) against influenza with respiratory failure treated with invasive mechanical ventilation., Conclusions: During an early 2022-2023 influenza season with a well-matched influenza vaccine, vaccination was associated with reduced risk of influenza-associated hospitalization and organ failure., Competing Interests: Potential conflicts of interest. S. B. reports participating as the DSMB chair for Hamilton Ventilators, outside the submitted work. J. C. reports receiving funding from the National Institutes of Health (NIH) and Department of Defense (DoD), and a travel grant from Fisher-Paykel, outside the submitted work. S. C. reports consulting for PureTech Health in 2021–2022 and Kiniksa Pharmaceuticals in 2022, outside the submitted work. A. D. reports participating on an advisory board for ALung Technologies and being a principal investigator (PI) for the PETAL Network, outside the submitted work. C. G. G. reports consulting fees from Merck and received research support from Campbell Alliance/Syneos Health, NIH, CDC, Food and Drug Administration (FDA), and AHRQ, outside the submitted work. M. N. G. reports receiving grant funding from NIH and AHRQ for research, honorarium for giving Medicine grand rounds at Yale and Washington Healthcare, fees for DSMB for Palm trial and Regeneron trials on monoclonal antibodies, and fees for serving on scientific advisory board for Philips Healthcare on monitoring, outside the submitted work. R. G. reports consulting for Gilead Sciences, Eli Lily, GSK, Janssen, and AbbVie, being on an advisory board for Gilead Sciences, Eli Lily, GlaxoSmithKline (GSK), and AstraZeneca, speaker bureau for Pfizer and AbbVie, and gift-in-kind to institution from Gilead Sciences, outside the submitted work. N. H. reports prior grant support from Sanofi and Quidel, and current funding from Merck, outside the submitted work. A. L. reports being a consultant for Roche on a clinical trial of baloxavir, outside the submitted work. Christopher Mallow reports medical legal consulting, outside the submitted work. I. P. reports receiving grants from NHLBI, NIGMS, and Janssen Pharmaceuticals and institutional support from Regeneron, outside the submitted work. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (Published by Oxford University Press on behalf of Infectious Diseases Society of America 2023.)

Importance: On June 21, 2023, the Centers for Disease Control and Prevention recommended the first respiratory syncytial virus (RSV) vaccines for adults aged 60 years and older using shared clinical decision-making. Understanding the severity of RSV disease in adults can help guide this clinical decision-making., Objective: To describe disease severity among adults hospitalized with RSV and compare it with the severity of COVID-19 and influenza disease by vaccination status., Design, Setting, and Participants: In this cohort study, adults aged 18 years and older admitted to the hospital with acute respiratory illness and laboratory-confirmed RSV, SARS-CoV-2, or influenza infection were prospectively enrolled from 25 hospitals in 20 US states from February 1, 2022, to May 31, 2023. Clinical data during each patient's hospitalization were collected using standardized forms. Data were analyzed from August to October 2023., Exposures: RSV, SARS-CoV-2, or influenza infection., Main Outcomes and Measures: Using multivariable logistic regression, severity of RSV disease was compared with COVID-19 and influenza severity, by COVID-19 and influenza vaccination status, for a range of clinical outcomes, including the composite of invasive mechanical ventilation (IMV) and in-hospital death., Results: Of 7998 adults (median [IQR] age, 67 [54-78] years; 4047 [50.6%] female) included, 484 (6.1%) were hospitalized with RSV, 6422 (80.3%) were hospitalized with COVID-19, and 1092 (13.7%) were hospitalized with influenza. Among patients with RSV, 58 (12.0%) experienced IMV or death, compared with 201 of 1422 unvaccinated patients with COVID-19 (14.1%) and 458 of 5000 vaccinated patients with COVID-19 (9.2%), as well as 72 of 699 unvaccinated patients with influenza (10.3%) and 20 of 393 vaccinated patients with influenza (5.1%). In adjusted analyses, the odds of IMV or in-hospital death were not significantly different among patients hospitalized with RSV and unvaccinated patients hospitalized with COVID-19 (adjusted odds ratio [aOR], 0.82; 95% CI, 0.59-1.13; P = .22) or influenza (aOR, 1.20; 95% CI, 0.82-1.76; P = .35); however, the odds of IMV or death were significantly higher among patients hospitalized with RSV compared with vaccinated patients hospitalized with COVID-19 (aOR, 1.38; 95% CI, 1.02-1.86; P = .03) or influenza disease (aOR, 2.81; 95% CI, 1.62-4.86; P < .001)., Conclusions and Relevance: Among adults hospitalized in this US cohort during the 16 months before the first RSV vaccine recommendations, RSV disease was less common but similar in severity compared with COVID-19 or influenza disease among unvaccinated patients and more severe than COVID-19 or influenza disease among vaccinated patients for the most serious outcomes of IMV or death.

Background: The COVID-19 pandemic was associated with historically low influenza circulation during the 2020-2021 season, followed by an increase in influenza circulation during the 2021-2022 US season. The 2a.2 subgroup of the influenza A(H3N2) 3C.2a1b subclade that predominated was antigenically different from the vaccine strain., Methods: To understand the effectiveness of the 2021-2022 vaccine against hospitalized influenza illness, a multistate sentinel surveillance network enrolled adults aged ≥18 years hospitalized with acute respiratory illness and tested for influenza by a molecular assay. Using the test-negative design, vaccine effectiveness (VE) was measured by comparing the odds of current-season influenza vaccination in influenza-positive case-patients and influenza-negative, SARS-CoV-2-negative controls, adjusting for confounders. A separate analysis was performed to illustrate bias introduced by including SARS-CoV-2-positive controls., Results: A total of 2334 patients, including 295 influenza cases (47% vaccinated), 1175 influenza- and SARS-CoV-2-negative controls (53% vaccinated), and 864 influenza-negative and SARS-CoV-2-positive controls (49% vaccinated), were analyzed. Influenza VE was 26% (95% CI: -14% to 52%) among adults aged 18-64 years, -3% (-54% to 31%) among adults aged ≥65 years, and 50% (15-71%) among adults aged 18-64 years without immunocompromising conditions. Estimated VE decreased with inclusion of SARS-CoV-2-positive controls., Conclusions: During a season where influenza A(H3N2) was antigenically different from the vaccine virus, vaccination was associated with a reduced risk of influenza hospitalization in younger immunocompetent adults. However, vaccination did not provide protection in adults ≥65 years of age. Improvements in vaccines, antivirals, and prevention strategies are warranted., Competing Interests: Potential conflicts of interest. M. G. reports grants from the Centers for Disease Control and Prevention (CDC), CDC-Abt Associates, CDC-Westat, and Janssen, and a leadership position as co-chair of the Infection Diseases and Immunizations Committee. J. S. S. reports a grant from the National Institutes of Health (NIH). A. D. reports grants from the NIH-PETAL Network, ACTIV-3b, ACTIV-4d, and GRAIL and consulting fees from Alung Technologies. M. E. P. reports a grant from the US Department of Defense and support for speaking at the 2022 North American Congress of Clinical Toxicology. I. D. P. reports grants from NIH, Janssen, Regeneron, and Asahi Kasei Pharma. D. N. H. reports grants from NIH (ACTIV-4d and Host Tissue-Nectar Trial). M. N. G. reports a grant from the National Heart, Lung, and Blood Institute (NHLBI); consulting fees for scientific advisory from Endpoint; support for attending an ATS Board of Executives Meeting; and participation in a Regeneron Data Safety and Monitoring Board (DSMB) for a monoclonal antibody trial. M. C. E. reports grants from NIH, Regeneron Pharmaceuticals, and payment from Abbott Labs for attending/lecture at the ASPEN Annual Meeting and on an Abbott webinar on nutrition in patients with COVID019. A. A. G. reports grants from NIH, Department of Defense, AbbVie, and Faron Pharmaceuticals. N. M. M. reports grants from the US CDC. E. T. M. reports grants from NIH and Merck and payment for lectures from the Michigan Infectious Diseases Society. K. W. G. reports grants from the Department of Defense and NIH support for ACTIV-4HT and Department of Defence support for Military Health System Research Symposium 2022 travel. J. H. K. is supported by grant 1K23AI137321-01A1 from the National Institute of Allergy and Infectious Diseases. N. H. reports grants from Sanofi and Quidel. A. S. L. reports grants from the US CDC, National Institute of Allergy and Infectious Diseases, and Burroughs Wellcome Fund; consulting fees from Sanofi and Roche; and membership on the American Society of Virology governing council (unpaid). C. J. L. reports grants from NIH, Department of Defense, CDC, bioMerieux, Entegrion Inc, Endpoint Health, Astra Zeneca, and AbbVie; patents for risk stratification in sepsis and septic shock issued to the Cincinnati Children's Hospital Medical Center; participation on DSMBs for clinical trials for Study Principal Investigators unrelated to the current work; and stock options in Bioscape Digital unrelated to the current work. C. G. G. reports grants from NIH, CDC, the Food and Drug Administration, the Agency for Healthcare Research and Quality, Sanofi, and Syneos Health and consulting fees from Pfizer, Merck, and Sanofi. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (Published by Oxford University Press on behalf of Infectious Diseases Society of America 2022.)

Background: Test-negative design (TND) studies have produced validated estimates of vaccine effectiveness (VE) for influenza vaccine studies. However, syndrome-negative controls have been proposed for differentiating bias and true estimates in VE evaluations for COVID-19. To understand the use of alternative control groups, we compared characteristics and VE estimates of syndrome-negative and test-negative VE controls., Methods: Adults hospitalized at 21 medical centers in 18 states March 11-August 31, 2021 were eligible for analysis. Case patients had symptomatic acute respiratory infection (ARI) and tested positive for SARS-CoV-2. Control groups were test-negative patients with ARI but negative SARS-CoV-2 testing, and syndrome-negative controls were without ARI and negative SARS-CoV-2 testing. Chi square and Wilcoxon rank sum tests were used to detect differences in baseline characteristics. VE against COVID-19 hospitalization was calculated using logistic regression comparing adjusted odds of prior mRNA vaccination between cases hospitalized with COVID-19 and each control group., Results: 5811 adults (2726 cases, 1696 test-negative controls, and 1389 syndrome-negative controls) were included. Control groups differed across characteristics including age, race/ethnicity, employment, previous hospitalizations, medical conditions, and immunosuppression. However, control-group-specific VE estimates were very similar. Among immunocompetent patients aged 18-64 years, VE was 93 % (95 % CI: 90-94) using syndrome-negative controls and 91 % (95 % CI: 88-93) using test-negative controls., Conclusions: Despite demographic and clinical differences between control groups, the use of either control group produced similar VE estimates across age groups and immunosuppression status. These findings support the use of test-negative controls and increase confidence in COVID-19 VE estimates produced by test-negative design studies., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: All authors have completed and submitted the International Committee of Medical Journal Editors (ICMJE) disclosure form. Funding for this work was provided to all participating sites by the United States Centers for Disease Control and Prevention. Samuel Brown reports grants from National Institutes of Health (NIH) and Department of Defense (DoD), participation as the DSMB chair for Hamilton Ventilators, and participation as a member of the DSMB for New York University COVID clinical trials. Jonathan Casey reports funding from NIH and DoD. Steven Chang reports consulting fees from La Jolla Pharmaceuticals, PureTech Health, and Kiniska Pharmaceuticals, payment/honoraria from La Jolla Pharmaceuticals, and participation on a DSMB for an investigator-initiated study conducted at UCLA. James Chappell reports grants and other support from NIH. Abhijit Duggal reports consulting fees from ALung technologies. Matthew Exline reports payment/honorariua from Abbott Lab for sponsored talks. D. Clark Files reports consulting fees from Cytovale and participation on a DSMB for Medpace. Anne Frosch reports grants from NIH. Manjusha Gaglani reports grants from Centers for Disease Control and Prevention (CDC), CDC-Abt Associates, CDC-Westat, and Janssen, and a leadership role as co-chair of the Infectious Disease and Immunization Committee of the Texas Pediatric Society, Texas Chapter of American Academy of Pediatrics. Kevin Gibbs reports funding from NIH/ National Heart, Lung, and Blood Institute (NHLBI) for the ACTIV-4HT NECTAR trial. Nicholas Mohr reports grants from the CDC (funded 2 other multicenter COVID-related projects separate from this work through payments to author’s institution). Adit Ginde reports grants from NIH, DoD, AbbVie, and Faron Pharmaceuticals. Michelle Gong reports grants from NIH/NHLBI and Agency for Healthcare Research and Quality (AHRQ), consulting fees from Endpoint, a leadership role on the American Thoracic Society (ATS) executive committee and board as well as support from ATS for meeting travel expenses, and participation on a DSMB for Regeneron. Carlos Grijalva reports grants from NIH, CDC, Food and Drug Administration (FDA), AHRQ, Sanofi, and Syneos Health and consulting fees from Pfizer, Merck, and Sanofi. David Hager reports grants from NIH/NHLBI for the ACTIV-4HT NECTAR trial and Incyte Corporation and participation as a DSMB chair for the SAFE EVICT Trial of vitamin C in COVID-19. Jennifer Wilson reports grants from the CDC and NIH (ARREST Pneumonia Trial UH3HL141722, ACTIV3a and 3b trials, and ACTIV4a trial), and membership on the American Board of Internal Medicine Critical Care Medicine exam committee. Natasha Halasa reports grants from NIH, Quidel, and Sanofi and honoraria for speaking at the American Academy of Pediatrics (AAP) conference. Nicholas Johnson reports grants from NIH/NHLBI/NINDS and the University of Washington Royalty Research Fund and payment for expert testimony for the Washington Department of Health. Akram Khan reports grants from United Therapeutics, Gilead Sciences, and 4D Medical and a leadership role on the guidelines committee for Chest. Jennie Kwon reports grants from NIH/NIAID. Adam Lauring reports grants from CDC, NIH/NIAID, and Burroughs Wellcome Fund and consulting fees from Sanofi and Roche. Christopher Lindsell reports grants from NIH, DoD, CDC, bioMerieux, Entegrion Inc., Endpoint Health, and AbbVie, patents for risk stratification in sepsis and septic shock, participation on DSMBs for clinical trials unrelated to the current work, a leadership role on the executive committee for the Board of Directors of the Association for Clinical and Translational Science, and stock options in Bioscape Digita. Emily Martin reports grants from Merck, CDC, and NIH and payment/honoraria from the Michigan Infectious Disease Society. Tresa McNeal reports payment/honoraria from the Society of Hospital Medicine. Ithan Peltan reports grants from NIH, Janssen, Regeneron, and Asahi Kasei Pharma. Todd Rice reports grants from AbbVie Inc., consulting fees from Cumberland Pharmaceuticals, Inc. and Cytovale, Inc., membership on a DSMB for Sanofi, Inc., a leadership role as immediate past president of the American Society of Parenteral and Enteral Nutrition, and stock options in Cumberland Pharmaceuticals, Inc. Wesley Self reports receiving the primary funding for this project from the United States Centers for Disease Control and Prevention, and research funding from Merck and Gilead Sciences. William Stubblefield reports grants from the NIH/NHLBI., (Published by Elsevier Ltd.)

Background . Adults in the United States (US) began receiving the adenovirus vector coronavirus disease 2019 (COVID-19) vaccine, Ad26.COV2.S (Johnson & Johnson [Janssen]), in February 2021. We evaluated Ad26.COV2.S vaccine effectiveness (VE) against COVID-19 hospitalization and high disease severity during the first 10 months of its use. Methods . In a multicenter case-control analysis of US adults (≥18 years) hospitalized 11 March to 15 December 2021, we estimated VE against susceptibility to COVID-19 hospitalization (VEs), comparing odds of prior vaccination with a single dose Ad26.COV2.S vaccine between hospitalized cases with COVID-19 and controls without COVID-19. Among hospitalized patients with COVID-19, we estimated VE against disease progression (VEp) to death or invasive mechanical ventilation (IMV), comparing odds of prior vaccination between patients with and without progression. Results . After excluding patients receiving mRNA vaccines, among 3979 COVID-19 case-patients (5% vaccinated with Ad26.COV2.S) and 2229 controls (13% vaccinated with Ad26.COV2.S), VEs of Ad26.COV2.S against COVID-19 hospitalization was 70% (95% confidence interval [CI]: 63-75%) overall, including 55% (29-72%) among immunocompromised patients, and 72% (64-77%) among immunocompetent patients, for whom VEs was similar at 14-90 days (73% [59-82%]), 91-180 days (71% [60-80%]), and 181-274 days (70% [54-81%]) postvaccination. Among hospitalized COVID-19 case-patients, VEp was 46% (18-65%) among immunocompetent patients. Conclusions . The Ad26.COV2.S COVID-19 vaccine reduced the risk of COVID-19 hospitalization by 72% among immunocompetent adults without waning through 6 months postvaccination. After hospitalization for COVID-19, vaccinated immunocompetent patients were less likely to require IMV or die compared to unvaccinated immunocompetent patients., Competing Interests: Potential conflicts of interest. M. G.: CDC: Baylor Scott & White Health (BSWH) US Flu/COVID VE Network, HAIVEN, Synergy studies; CDC-Abt: BSWH FluVax Trial and RECOVER-PROTECT Cohort Studies; CDC-Westat: BSWH VISION COVID-Flu VE Study; Janssen: BSWH Respiratory Syncytial Virus (RSV) Severity App Birth Cohort Study; Co-Chair of Infectious Diseases and Immunization Committee—Texas Pediatric Society—Texas Chapter of American Academy of Pediatrics. A. G.: National Institutes of Health (NIH), Department of Defense; Faron Pharmaceuticals; AbbVie; D Douin: NIH/National Institute of General Medical Sciences (NIGMS) Institutional Training Grant. J. C.: NIH and Department of Defense grants unrelated to this work. T. A. M.: Panelist for Society of Hospital Medicine Updates in Heart Failure; Board member for Scott & White Clinic Physicians Board of Directors. K. G.: NECTAR Executive Committee member ACTIV4-HT; D. C. F.: Cytovale consulting fees; Medpace Data Safety Monitoring Board. D. N. H.: National Heart, Lung, and Blood Institute (NIHLBI) participant in the ACTIV4d-Host Tissue Trial; Chair DSMD—SAFE EVICT Trial of VIT C in COVID-19. M. N. G.: Grants from NHLBI and Agency for Healthcare Research and Quality (AHRQ); Consulting fees for Endpoint for scientific advisory panel; Honoraria—Medicine Grand Rounds from Westchester Medical Center; Support for attending ATS Board of Directors meeting; Data and Safety Monitoring Board (DSMB) for Regeneron study and REPLENISH trial. N. J. J.: IH grants paid to University of Washington Royalty Research Fund; Department of Defense grants; Medic One Foundation grants; WA Department of Health expert testimony payment; DSMB for Opticyte, Inc.; Chair, ACEP Critical Care Section. I. P.: NIH grants; Regeneron Pharmaceuticals grant; Intermountain Research & Medical Foundation grant; Asahi Kasei Pharma grant; Janssen Pharmaceuticals grant. S. B.: NIH grants and Department of Defense grants; DSMB for Hamilton ventilators and NYU. E. T. M.: Merck grant. A. S. M.: NIH grant. A. K.: NIH grants; United Therapeutics grants; Eli Lily grants; Johnson & Johnson—BOA Medical—4DMedical research grants; rA. D.: Center PI for PETAL network through NHLBI grant; on steering committee for A Lung technologies. J. G. W.: NIH/NHLBI funding for ACTIV-3 and ACTIV-4 trials; American Board of Internal Medicine—member of Critical Care Exam Committee. S. Y. C.: Consulting fees for PureTech Health and Kiniska Pharmaceuticals; Honoraria for La Jolla. H. M. B.: CDC grant for HCP COVID vaccine effectiveness. J. H. K.: NIAID grant. M. C. E.: Abbott Labs honoraria for speaking on ASPEN on nutrition in critical illness from COVID. A. L.: grants from CDC, NIH, and Burroughs Wellcome Fund; consulting fees from Sanofi on antiviral drugs and for Roche on baloxavir trial steering committee. N. H.: grants from NIH, Quidel, and Sanofi; Honoraria for speaking at CME event at AAP. C. G. G.: grants from Campbell Alliance/Syneos Health, Sanofi, CDC, AHRQ, NIH, and FDA; consulting fees from Merck, Pfizer, and Sanofi-Pasteur. T. W. R.: grants from NIH, Department of Defense and AbbVie; consulting fees for Cumberland Pharmaceuticals, Inc. and Cytovale, Inc.; DSMB for Sanofi, Inc.; Immediate Past President—ASPEN; Stock in Cumberland Pharmaceuticals, Inc. for consulting work. W. B. S.: NIH training grants. C. J. L.: grants from NIH, Department of Defense; CDC; bioMerieux; Entegrion, Inc.; Endpoint Health; AbbVie; Patents for risk stratification in sepsis and septic shock issued to Cincinnati Children’s Hospital Medical Center; DSMBs for clinical trials for Study Principal Investigators; Association for Clinical and Translational Science (Executive Committee, Immediate Past President, and Board of Directors); stock options in Bioscape Digita. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (Published by Oxford University Press on behalf of the Infectious Diseases Society of America 2022.)

Background: Test-negative design studies for evaluating influenza vaccine effectiveness (VE) enroll patients with acute respiratory infection. Enrollment typically occurs before influenza status is determined, resulting in over-enrollment of influenza-negative patients. With availability of rapid and accurate molecular clinical testing, influenza status could be ascertained before enrollment, thus improving study efficiency. We estimate potential biases in VE when using clinical testing., Methods: We simulate data assuming 60% vaccinated, 25% of those vaccinated are influenza positive, and VE of 50%. We show the effect on VE in 5 scenarios., Results: Vaccine effectiveness is affected only when clinical testing preferentially targets patients based on both vaccination and influenza status. Vaccine effectiveness is overestimated by 10% if nontesting occurs in 39% of vaccinated influenza-positive patients and 24% of others. VE is also overestimated by 10% if nontesting occurs in 8% of unvaccinated influenza-positive patients and 27% of others. Vaccine effectiveness is underestimated by 10% if nontesting occurs in 32% of unvaccinated influenza-negative patients and 18% of others., Conclusions: Although differential clinical testing by vaccine receipt and influenza positivity may produce errors in estimated VE, bias in testing would have to be substantial and overall proportion of patients tested would have to be small to result in a meaningful difference in VE., (Published by Oxford University Press for the Infectious Diseases Society of America 2021.)

Background: Influenza vaccine effectiveness (VE) against a spectrum of severe disease, including critical illness and death, remains poorly characterized., Methods: We conducted a test-negative study in an intensive care unit (ICU) network at 10 US hospitals to evaluate VE for preventing influenza-associated severe acute respiratory infection (SARI) during the 2019-2020 season, which was characterized by circulation of drifted A/H1N1 and B-lineage viruses. Cases were adults hospitalized in the ICU and a targeted number outside the ICU (to capture a spectrum of severity) with laboratory-confirmed, influenza-associated SARI. Test-negative controls were frequency-matched based on hospital, timing of admission, and care location (ICU vs non-ICU). Estimates were adjusted for age, comorbidities, and other confounders., Results: Among 638 patients, the median (interquartile) age was 57 (44-68) years; 286 (44.8%) patients were treated in the ICU and 42 (6.6%) died during hospitalization. Forty-five percent of cases and 61% of controls were vaccinated, which resulted in an overall VE of 32% (95% CI: 2-53%), including 28% (-9% to 52%) against influenza A and 52% (13-74%) against influenza B. VE was higher in adults 18-49 years old (62%; 95% CI: 27-81%) than those aged 50-64 years (20%; -48% to 57%) and ≥65 years old (-3%; 95% CI: -97% to 46%) (P = .0789 for interaction). VE was significantly higher against influenza-associated death (80%; 95% CI: 4-96%) than nonfatal influenza illness., Conclusions: During a season with drifted viruses, vaccination reduced severe influenza-associated illness among adults by 32%. VE was high among young adults., (© The Author(s) 2021. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

With rapid and accurate molecular influenza testing now widely available in clinical settings, influenza vaccine effectiveness (VE) studies can prospectively select participants for enrollment based on real-time results rather than enrolling all eligible patients regardless of influenza status, as in the traditional test-negative design (TND). Thus, we explore advantages and disadvantages of modifying the TND for estimating VE by using real-time, clinically available viral testing results paired with acute respiratory infection eligibility criteria for identifying influenza cases and test-negative controls prior to enrollment. This modification, which we have called the real-time test-negative design (rtTND), has the potential to improve influenza VE studies by optimizing the case-to-test-negative control ratio, more accurately classifying influenza status, improving study efficiency, reducing study cost, and increasing study power to adequately estimate VE. Important considerations for limiting biases in the rtTND include the need for comprehensive clinical influenza testing at study sites and accurate influenza tests., (Published by Oxford University Press for the Infectious Diseases Society of America 2020.)

Solid organ transplant (SOT) recipients are at increased risk of influenza disease and associated complications. The mainstay of prevention is the annual standard-dose influenza vaccine, as studies showed decreased influenza-related morbidity and mortality in vaccinated SOT recipients compared to those unvaccinated. Nonetheless, the immune response in this high-risk population is suboptimal compared to healthy individuals. Over the past two decades, several vaccination strategies have been investigated to overcome this inadequate immune response in SOT recipients. Howbeit, the best vaccination strategy and optimal timing of influenza vaccination remain unclear. This review will provide a detailed summary of studies of various influenza vaccination strategies in adult SOT recipients, discussing immunogenicity results, and addressing their limitations and knowledge gaps., (© 2020 The American Society of Transplantation and the American Society of Transplant Surgeons.)

Increasing use of immunosuppressive biologic therapies poses a challenge for infectious diseases. Immunosuppressed patients have a high risk for influenza complications and an impaired immune response to vaccines. The total burden of immunosuppressive conditions in the United States, including those receiving emerging biologic therapies, remains unknown. We used the national claims database MarketScan to estimate the prevalence of immunosuppressive conditions and risk for acute respiratory illnesses (ARIs). We studied 47.2 million unique enrollees, representing 115 million person-years of observation during 2012-2017, and identified immunosuppressive conditions in 6.2% adults 18-64 years of age and 2.6% of children <18 years of age. Among 542,105 ARI hospitalizations, 32% of patients had immunosuppressive conditions. The risk for ARI hospitalizations was higher among enrollees with immunosuppression than among nonimmunosuppressed enrollees. Future efforts should focus on developing improved strategies, including vaccines, for preventing influenza in immunosuppressed patients, who are an increasing population in the United States.

Although the 2017-2018 influenza season had very high rates of influenza-associated illness, the 2018-2019 influenza season was comparable to previous seasons. Influenza A was the most commonly identified type worldwide, although variations in influenza A subtype prevalence existed. Influenza vaccination remains the single most effective way to prevent influenza-associated illness. A novel influenza antiviral, baloxavir, has demonstrated promising results; however, concerns about development of resistance exist., (© 2019 Wiley Periodicals, Inc.)

The 2017-18 influenza season brought record numbers of cases in both the Northern and Southern hemispheres, resulting in high rates of influenza-related hospital admission and death. Estimated efficacy of flu vaccine was low against the most common circulating strain, influenza A (H3N2). Decreased efficacy may be due to changes in circulating virus or mutations that occur in the vaccine strain during the manufacturing process., (© 2018 Wiley Periodicals, Inc.)

Influenza-associated infections cause significant morbidity and mortality worldwide, particularly among immunocompromised patients. Immunization is the primary mode of prevention of disease; however, efficacy in immunocompromised patients may be limited. Antiviral medications are important for treatment and prophylaxis of affected individuals. This article reviews treatment and prevention recommendations for the 2016-2017 influenza season in the Northern Hemisphere and Southern Hemisphere., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Although children with acute lymphoblastic leukemia (ALL) mount immune responses after vaccination with the trivalent influenza vaccine (TIV), these responses are lower compared to controls. Recently, a high dose (HD) TIV was found to increase the level of antibody response in elderly patients compared to the standard dose (SD) TIV. We hypothesized that the HD TIV would be well-tolerated and more immunogenic compared to the SD TIV in pediatric subjects with ALL., Procedure: This was a randomized, double-blind, phase I safety trial comparing the HD to the SD TIV in children with ALL. Our secondary objective was immunogenicity. Subjects were randomized 2:1 to receive either the HD (60 µg) or the SD (15 µg) TIV. Local and systemic reactions were solicited, hemagglutinin inhibition titers to influenza virus antigens were measured, and monitoring labs were collected prior to and/or after each vaccination., Results: Fifty subjects were enrolled (34 HD, 16 SD). Mean age was 8.5 years; 63% were male, and 80% were in maintenance therapy. There were no significant differences reported in local or systemic symptoms. No severe adverse events were attributed to vaccination. No significant differences between the HD and SD TIV groups were noted for immune responses., Conclusions: No differences were noted between the HD and SD TIV groups for solicited systemic and local reactions. Since this study was not powered for immunogenicity, a phase II trial is needed to determine the immunogenicity of HD versus SD TIV in the pediatric ALL population., (© 2013 Wiley Periodicals, Inc.)

Influenza virus causes a spectrum of illness in transplant recipients with a high rate of lower respiratory disease. Seasonal influenza vaccination is an important public health measure recommended for transplant recipients and their close contacts. Vaccine has been shown to be safe and generally well tolerated in both adult and pediatric transplant recipients. However, responses to vaccine are variable and are dependent on various factors including time from transplantation and specific immunosuppressive medication. Seasonal influenza vaccine has demonstrated safety and no conclusive evidence exists for a link between vaccination and allograft dysfunction. Annually updated trivalent inactivated influenza vaccines have been available and routinely used for several decades, although newer influenza vaccination formulations including high-dose vaccine, adjuvanted vaccine, quadrivalent inactivated vaccine and vaccine by intradermal delivery system are now available or will be available in the near future. Safety and immunogenicity data of these new formulations in transplant recipients requires investigation. In this document, we review the current state of knowledge on influenza vaccines in transplant recipients and make recommendations on the use of vaccine in both adult and pediatric organ transplant recipients., (©Copyright 2011 The American Society of Transplantation and the American Society of Transplant Surgeons.)

Background: The safety of intranasal live-attenuated influenza vaccine (LAIV) in immunocompromised children with cancer is unknown. The objective of this study was to describe the safety and immunogenicity of LAIV in mild to moderately immunocompromised children with cancer., Methods: We conducted a multicenter, randomized, double-blind study of LAIV versus placebo in children aged 5-17 years with cancer. LAIV (frozen formulation) or allantoic fluid/buffer was administered intranasally. Reactogenicity, adverse events, blood for immune assays, and nasal swabs for viral shedding were obtained during 5 visits over the first 42 days postvaccination; information concerning serious adverse events (SAEs) was collected for 180 days., Results: 20 subjects were enrolled (LAIV, n=10; placebo, n=10) with a mean age of 12.2 years. Ten subjects had hematologic malignancy (LAIV, n=4; placebo, n=6); 10 subjects had solid tumors (LAIV, n=6; placebo, n=4). One subject was excluded from immunogenicity analysis for not receiving a full dose of LAIV. LAIV resulted in an increased incidence of runny nose/nasal congestion occurring in all LAIV recipients; no related SAEs were observed. Four of 10 LAIV recipients shed vaccine virus, with none exceeding 7-10 days duration. LAIV demonstrated modest immunogenicity by hemagglutination inhibition (≥ 4 fold rise for any strain, 33%) and microneutralization assays (≥ 4 fold rise for any strain, 44%)., Conclusion: In this small pilot study conducted in mild to moderately immunocompromised children with cancer, runny nose/nasal congestion was increased in LAIV recipients, no related SAEs occurred, and prolonged viral shedding was not detected. Moderate immunogenicity was demonstrated in this small group of individuals., (Copyright © 2011 Elsevier Ltd. All rights reserved.)