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The COVID-19 pandemic caused an abrupt drop in in-person health care (inpatient, Emergency Department, outpatient) and an increase in telehealth care, which poses challenges in vaccine safety studies that identify outcomes from in-person encounters. We examined the changes in incidence rates of selected encounter-based outcomes during the COVID-19 pandemic.We assembled a cohort of members from 8 Vaccine Safety Datalink sites from January 1, 2017 through December 31, 2020. Using ICD-10 diagnosis codes or laboratory criteria, we identified 21 incident outcomes in traditional in-person settings and all settings. We defined 4 periods in 2020: January-February (pre-pandemic), April-June (early pandemic), July-September (middle pandemic), and October-December (late pandemic). We defined four corresponding periods in each year during 2017-2019. We calculated incidence rates, conducted difference in difference (DiD) analyses, and reported ratios of incidence rate ratios (RRR) to examine changes in rates from pre-pandemic to early, middle, and late pandemic in 2020, after adjusting for changes across similar periods in 2017-2019.Among 10 million members, regardless of setting and after adjusting for changes during 2017-2019, we found that incidence rates of acute disseminated encephalomyelitis, encephalitis/myelitis/encephalomyelitis/meningoencephalitis, and thrombotic thrombocytopenic purpura did not significantly change from the pre-pandemic to early, middle or late pandemic periods (p-values ≥ 0.05). Incidence rates decreased from the pre-pandemic to early pandemic period during 2020 for acute myocardial infarction, anaphylaxis, appendicitis, Bell's palsy, convulsions/seizures, Guillain-Barré syndrome, immune thrombocytopenia (ITP), narcolepsy/cataplexy, hemorrhagic stroke, ischemic stroke, and venous thromboembolism (p-values 0.05). Incidence rates of Bell's palsy, ITP, and narcolepsy/cataplexy were higher in all settings than in traditional in-person settings during the three pandemic periods (p-values 0.05).Rates of some clinical outcomes during the pandemic changed and should not be used as historical background rates in vaccine safety studies. Inclusion of telehealth visits should be considered for vaccine studies involving Bell's palsy, ITP, and narcolepsy/cataplexy.

BACKGROUND Understanding the long-term impact of the COVID-19 pandemic on health care utilization is important to health care organizations and policy makers, as well for researchers when designing studies that use observational electronic health record data during the pandemic period. OBJECTIVE To evaluate changes in health care utilization across all care settings among a large diverse insured population in the United States during the COVID-19 pandemic. METHODS We conducted a retrospective cohort study within 8 health care organizations participating in the Vaccine Safety Datalink Project using electronic health record data from members of all ages during January 2017 - December 2021. The visit rates per person-year were calculated monthly during the study period for all health care settings combined as well as by inpatient, emergency department (ED), outpatient, and telehealth settings, both among all members and members without COVID-19. Difference-in-difference analysis and interrupted time series analysis were performed to assess the changes in visit rates from the pre-pandemic period (January 2017 to February 2020) to the early pandemic period (April 2020 to December 2020) and the later pandemic period (July 2021 to December 2021), respectively. RESULTS The study included more than 11 million members between 2017 and 2021. Compared with the pre-pandemic period, we found reductions in visit rates during the early pandemic period for all in-person care settings. During the later pandemic period, overall utilization exceeded pre-pandemic levels (adjusted percent change = 5.1%; 95% CI 0.6% to 9.9%); inpatient and ED visits returned to pre-pandemic levels, although they remained 7.5% and 8.0% lower among members without a documented history of COVID-19. Telehealth visits, which were approximately 42% of the volume of outpatient visits during the later pandemic period, were increased by 97.5% (95% CI 86.0% to 109.7%) from the pre-pandemic period. CONCLUSIONS Our findings provide valuable information for longer-term strategic resource allocation for patient care in the post-pandemic period and for designing observational studies involving the pandemic period.

Since 2006, the US human papillomavirus (HPV) vaccination program has led to decreases in HPV infections caused by high-risk vaccine-targeted HPV types (HPV 16/18). We assessed differences in high-risk HPV prevalence by cervical cytology result among 20- to 24-year-old persons participating in routine cervical cancer screening in 2015-2017 compared with 2007.Residual routine cervical cancer screening specimens were collected from 20- to 24-year-old members of 2 integrated healthcare delivery systems as part of a cross-sectional study and were tested for 37 HPV types. Cytology results and vaccination status (≥1 dose) were extracted from medical records. Cytology categories were normal, atypical squamous cells of undefined significance, low-grade squamous intraepithelial lesions (SIL), or high-grade SIL/atypical squamous cells cannot exclude high-grade SIL. Prevalences of HPV categories (HPV 16/18, HPV 31/33/45/52/58, HPV 35/39/51/56/59/66/68) were estimated by cytology result for 2007 and 2015-2017.Specimens from 2007 (n = 4046) were from unvaccinated participants; 4574 of 8442 specimens (54.2%) from 2015-2017 were from vaccinated participants. Overall, HPV 16/18 positivity was lower in 2015-2017 compared with 2007 in all groups: high-grade SIL/atypical squamous cells cannot exclude high-grade SIL, 16.0% vs 69.2%; low-grade SIL, 5.4% vs 40.1%; atypical squamous cells of undefined significance, 5.0% vs 25.6%; and normal, 1.3% vs 8.1%. Human papillomavirus 31/33/45/52/58 prevalence was stable for all cytology groups; HPV 35/39/51/56/59/66/68 prevalence increased among low-grade SIL specimens (53.9% to 65.2%) but remained stable in other groups.Prevalence of vaccine-targeted high-risk HPV types 16/18 was dramatically lower in 2015-2017 than 2007 across all cytology result groups while prevalence of other high-risk HPV types was mainly stable, supporting vaccine impact with no evidence of type replacement.

COVID-19 vaccines are critical for ending the COVID-19 pandemic; however, current data about vaccination coverage and safety in pregnant women are limited. Pregnant women are at increased risk for severe illness and death from COVID-19 compared with nonpregnant women of reproductive age, and are at risk for adverse pregnancy outcomes, such as preterm birth (1-4). Pregnant women are eligible for and can receive any of the three COVID-19 vaccines available in the United States via Emergency Use Authorization.* Data from Vaccine Safety Datalink (VSD), a collaboration between CDC and multiple integrated health systems, were analyzed to assess receipt of ≥1 dose (first or second dose of the Pfizer-BioNTech or Moderna vaccines or a single dose of the Janssen [Johnson & Johnson] vaccine) of any COVID-19 vaccine during pregnancy, receipt of first dose of a 2-dose COVID-19 vaccine (initiation), or completion of a 1- or 2-dose COVID-19 vaccination series. During December 14, 2020-May 8, 2021, a total of 135,968 pregnant women were identified, 22,197 (16.3%) of whom had received ≥1 dose of a vaccine during pregnancy. Among these 135,968 women, 7,154 (5.3%) had initiated and 15,043 (11.1%) had completed vaccination during pregnancy. Receipt of ≥1 dose of COVID-19 vaccine during pregnancy was highest among women aged 35-49 years (22.7%) and lowest among those aged 18-24 years (5.5%), and higher among non-Hispanic Asian (Asian) (24.7%) and non-Hispanic White (White) women (19.7%) than among Hispanic (11.9%) and non-Hispanic Black (Black) women (6.0%). Vaccination coverage increased among all racial and ethnic groups over the analytic period, likely because of increased eligibility for vaccination† and increased availability of vaccine over time. These findings indicate the need for improved outreach to and engagement with pregnant women, especially those from racial and ethnic minority groups who might be at higher risk for severe health outcomes because of COVID-19 (4). In addition, providing accurate and timely information about COVID-19 vaccination to health care providers, pregnant women, and women of reproductive age can improve vaccine confidence and coverage by ensuring optimal shared clinical decision-making.

Background Human papillomavirus (HPV) vaccine has been recommended in the United States since 2006 for routine vaccination of girls at age 11–12 years and through age 26 years for women not previously vaccinated. Changes in vaccine-type HPV (VT) prevalence can be used to evaluate vaccine impact, including herd effects. Methods We determined type-specific HPV in cytology specimens from women aged 20–29 years screened for cervical cancer at Kaiser Permanente Northwest in 2007 and in two vaccine era periods: 2012–2013 and 2015–2016. Detection and typing used L1 consensus PCR with hybridization for 37 types, including quadrivalent vaccine types (HPV 6/11/16/18). Results Among 20–24 year-olds in 2012–2013 and 2015–2016, 44% and 64% had a history of ≥1-dose vaccination. VT prevalence decreased from 13.1% in 2007 to 2.9% in 2015–2016 (prevalence ratio [PR] = 0.22; 95% confidence interval [CI] 0.17–0.29). HPV 31 prevalence was also lower in the vaccine periods compared with 2007. VT prevalence in 2015–2016 among 20–24 year-olds was lower in both vaccinated, 1.3% (PR = 0.10; 95% CI 0.06–0.16), and unvaccinated women, 5.8% (PR = 0.45; 95% CI 0.33–0.61). Among 25–29 year-olds, 21% and 32% had a history of ≥1-dose vaccination. VT prevalence decreased from 8.1% in 2007 to 5.0% in 2015–2016 (PR = 0.62; 95% CI 0.50–0.78). Non-VT high risk prevalence was higher in the vaccine periods compared with the pre-vaccine era in both age groups, however, not in 2015–2016 compared with 2012–2013. Conclusion Within 9–10 years of vaccine introduction, VT prevalence decreased 78% among 20–24 year-olds and 38% in 25–29 year-olds. There were declines in both vaccinated and unvaccinated women, showing evidence of direct and herd protection.

Background The Vaccine Safety Datalink (VSD) uses vaccination data from electronic health records (EHR) at eight integrated health systems to monitor vaccine safety. Accurate capture of data from vaccines administered outside of the health system is critical for vaccine safety research, especially for COVID-19 vaccines, where many are administered in non-traditional settings. However, timely access and inclusion of data from Immunization Information Systems (IIS) into VSD safety assessments is not well understood. Methods We surveyed the eight data-contributing VSD sites to assess: 1) status of sending data to IIS; 2) status of receiving data from IIS; and 3) integration of IIS data into the site EHR. Sites reported separately for COVID-19 vaccination to capture any differences in capacity to receive and integrate data on COVID-19 vaccines versus other vaccines. Results All VSD sites send data to and receive data from their state IIS. All eight sites (100%) routinely integrate IIS data for COVID-19 vaccines into VSD research studies. Six sites (75%) also routinely integrate all other vaccination data; two sites integrate data from IIS following a reconciliation process, which can result in delays to integration into VSD datasets. Conclusions COVID-19 vaccines are being administered in a variety of non-traditional settings, where IIS are commonly used as centralized reporting systems. All eight VSD sites receive and integrate COVID-19 vaccine data from IIS, which positions the VSD well for conducting quality assessments of vaccine safety. Efforts to improve the timely receipt of all vaccination data will improve capacity to conduct vaccine safety assessments within the VSD.

Background: Identifying pregnancy episodes and accurately estimating their beginning and end dates are imperative for observational maternal vaccine safety studies using electronic health record (EHR) data. Methods: We modified the Vaccine Safety Datalink (VSD) Pregnancy Episode Algorithm (PEA) to include both the International Classification of Disease, ninth revision (ICD-9 system) and ICD-10 diagnosis codes, incorporated additional gestational age data, and validated this enhanced algorithm with manual medical record review. We also developed the new Dynamic Pregnancy Algorithm (DPA) to identify pregnancy episodes in real time. Results: Around 75% of the pregnancy episodes identified by the enhanced VSD PEA were live births, 12% were spontaneous abortions (SABs), 10% were induced abortions (IABs), and 0.4% were stillbirths (SBs). Gestational age was identified for 99% of live births, 89% of SBs, 69% of SABs, and 42% of IABs. Agreement between the PEA-assigned and abstractor-identified pregnancy outcome and outcome date was 100% for live births, but was lower for pregnancy losses. When gestational age was available in the medical record, the agreement was higher for live births (97%), but lower for pregnancy losses (75%). The DPA demonstrated strong concordance with the PEA and identified pregnancy episodes ⩾6 months prior to the outcome date for 89% of live births. Conclusion: The enhanced VSD PEA is a useful tool for identifying pregnancy episodes in EHR databases. The DPA improves the timeliness of pregnancy identification and can be used for near real-time maternal vaccine safety studies. Plain Language Summary Improving identification of pregnancies in the Vaccine Safety Datalink electronic medical record databases to allow for better and faster monitoring of vaccination safety during pregnancy Introduction: It is important to monitor of the safety of vaccines after they have been approved and licensed by the Food and Drug Administration, especially among women vaccinated during pregnancy. The Vaccine Safety Datalink (VSD) monitors vaccine safety through observational studies within large databases of electronic medical records. Since 2012, VSD researchers have used an algorithm called the Pregnancy Episode Algorithm (PEA) to identify the medical records of women who have been pregnant. Researchers then use these medical records to study whether receiving a particular vaccine is linked to any negative outcomes for the woman or her child. Methods: The goal of this study was to update and enhance the PEA to include the full set of medical record diagnostic codes [both from the older International Classification of Disease, ninth revision (ICD-9 system) and the newer ICD-10 system] and to incorporate additional sources of data about gestational age. To ensure the validity of the PEA following these enhancements, we manually reviewed medical records and compared the results with the algorithm. We also developed a new algorithm, the Dynamic Pregnancy Algorithm (DPA), to identify women earlier in pregnancy, allowing us to conduct more timely vaccine safety assessments. Results: The new version of the PEA identified 2,485,410 pregnancies in the VSD database. The enhanced algorithm more precisely estimated the beginning of pregnancies, especially those that did not result in live births, due to the new sources of gestational age data. Conclusion: Our new algorithm, the DPA, was successful at identifying pregnancies earlier in gestation than the PEA. The enhanced PEA and the new DPA will allow us to better evaluate the safety of current and future vaccinations administered during or around the time of pregnancy.

This study uses data from the Vaccine Safety Datalink on receipt of booster doses of COVID-19 vaccines among pregnant individuals aged 18 to 49 years.

Reports of myocarditis and pericarditis following smallpox vaccination in adults suggested a need to assess inflammatory cardiac disease risk among adults who receive live viral vaccinations. From 1996 through 2007, among 416,629 vaccinated adults in the Vaccine Safety Datalink, we identified one probable pericarditis case and no cases of myocarditis in the 42 days following a live viral vaccination. Our self-controlled risk interval analysis found that, based on one case identified during the risk interval and 10 cases during the control interval, there is no increased risk of myopericarditis in the 42 days following vaccination (IRR, 0.57; 95% CI, 0.07, 4.51). Our study suggests that the occurrence of myopericarditis following live viral vaccination is rare with an estimated incidence of 0.24 per 100,000 vaccinated, which is not higher than the background rate and is much lower than the incidence rates reported following smallpox vaccination.

We examined the effectiveness of human papillomavirus vaccination by dose number and spacing against incident genital warts in a cohort of 64,517 female health-plan enrollees in the United States during 2006-2012. Eligible recipients were classified into groups by regimen: 0, 1, 2 (

BACKGROUND Studies in countries with high human papillomavirus (HPV) vaccination coverage have demonstrated marked reductions in anogenital wart (AGW) incidence. Our goal was to assess the impact of HPV vaccination in a population with suboptimal coverage by comparing AGW incidence trends in the years before and after vaccine introduction. METHODS We conducted a retrospective analysis of AGW incidence trends using an ecologic study design among 11- through 39-year-olds enrolled at Kaiser Permanente Northwest. We defined incidence as the proportion of persons who had a new AGW diagnosis for each calendar year in the prevaccine periods (2000 through 2006 for female individuals, 2000 through 2010 for male individuals) and the postvaccine periods (2007 through 2016 for female individuals, 2011 through 2016 for male individuals). We also described cumulative HPV vaccination coverage. RESULTS The average annual AGW incidence rates in the prevaccine periods were 27.8 per 10,000 in female individuals and 26.9 per 10,000 in male individuals. In the postvaccine periods, AGW incidence rates decreased by 31% (P < 0.001) in female individuals and 10% (P = 0.006) in male individuals; the largest reductions were observed in 15- to 19-year-old female individuals (67%, P < 0.001) and male individuals (45%, P < 0.001). Three dose HPV coverage rates were less than 50% in all age groups and both sexes. CONCLUSIONS In a population of young adults with moderate HPV vaccination coverage, we observed declines in AGW incidence among both female and male year after the introduction of HPV vaccination. The largest incidence reductions were observed in 15- to 19-year-olds who were most likely to have been vaccinated.

BACKGROUND: Published case series have suggested a potential association between human papillomavirus (HPV) vaccination and primary ovarian insufficiency (POI). We describe POI incidence and estimate POI risk after HPV; tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis, adsorbed (Tdap); inactivated influenza (II); and meningococcal conjugate (MenACWY) vaccination. METHODS: We searched Kaiser Permanente Northwest electronic health records for outpatient diagnoses suggestive of POI in female patients aged 11 to 34 years between 2006 and 2014. We reviewed and adjudicated the medical record to confirm diagnoses and estimate symptom onset dates. We excluded cases with known causes and calculated the incidence of idiopathic POI. We estimated risk by calculating hazard ratios and 95% confidence intervals (CIs). RESULTS: From a cohort of 199 078 female patients, we identified 120 with diagnoses suggestive of POI. After adjudication and exclusion of 26 POI cases with known causes, we confirmed 46 idiopathic POI cases. POI incidence was low in 11- to 14-year-olds (0.87 per 1 000 000 person-months) and increased with age. One confirmed case patient received the HPV vaccine 23 months before the first clinical evaluation for delayed menarche. The adjusted hazard ratio was 0.30 (95% CI: 0.07–1.36) after HPV, 0.88 (95% CI: 0.37–2.10) after Tdap, 1.42 (95% CI: 0.59–3.41) after II, and 0.94 (95% CI: 0.27–3.23) after MenACWY vaccination. CONCLUSIONS: We did not find a statistically significant elevated risk of POI after HPV, Tdap, II, or MenACWY vaccination in this population-based retrospective cohort study. These findings should lessen concern about POI risk after adolescent vaccination.

BACKGROUND In the United States, human papillomavirus (HPV) vaccine is recommended for 11- or 12-year-olds, and for young adults not previously vaccinated. Early vaccine impact can be measured by reductions in vaccine-type (VT) HPV prevalence. METHODS Consecutive residual cervical specimens were retained from women aged 20-29 years at Kaiser Permanente Northwest in 2007, 2012, and 2013. HPV genotypes were determined using L1 consensus polymerase chain reaction with type-specific hybridization to detect 37 types, including VT HPV (HPV type 6, 11, 16, and 18). We compared HPV prevalence in 2007 and 2012-2013, and we evaluated predictors of VT HPV and any-HPV prevalence in 2012-2013. RESULTS In 2012-2013, 31.9% of 4181 women had initiated HPV vaccination. VT HPV prevalence decreased from 10.6% in 2007 to 6.2% in 2012-2013 (P < .001). In 2012-2013, VT HPV prevalence was significantly lower among those who initiated vaccination

CONTEXT Pregnant women are at increased risk of severe influenza-related complications and hospitalizations and are a priority group for influenza vaccination. OBJECTIVE To examine coverage of seasonal and pandemic influenza A (H1N1) vaccines in pregnant women in a managed care setting, from 2008 to 2012. DESIGN Retrospective cohort study of 10,145 pregnant women. MAIN OUTCOME MEASURES H1N1 and seasonal influenza vaccination rates. RESULTS Seasonal influenza vaccine coverage increased from 38% to 63% between the 2008-2009 and 2010-2011 seasons, and then dropped to 61% in 2011-2012. Vaccine coverage was higher in women considered at high risk of influenza complications, increasing from 43% in 2008-2009 to 71% in 2010-2011, before decreasing to 69% in 2011-2012. H1N1 vaccine coverage was greater than seasonal influenza coverage in 2009-2010 in the overall pregnant population (61% vs 53%) and in the high-risk group (64% vs 59%). We observed statistically significant differences in vaccination rates by trimester, gravidity, maternal age, and race/ethnicity. CONCLUSIONS Vaccination rates increased significantly from 2008 to 2011, then dropped slightly in 2011-2012. Continued efforts are needed to ensure adequate vaccination coverage in this high-risk population.

Mass vaccination campaigns during which new vaccines may be administered to many millions of people in a short period of time call for timely and accurate post-licensure surveillance to monitor vaccine safety. To address the need for timely H1N1 influenza vaccine safety information during the 2009-2010 H1N1 influenza pandemic, the Vaccine Safety Datalink (VSD) project assessed the feasibility and potential mechanisms for utilizing data from state and local immunization registries to capture vaccinations that would not otherwise be captured by the data systems of the participating VSD managed care organizations (MCOs). Three of the eight VSD sites were able to capture H1N1 immunization data electronically from the state and local registries, and one site was able to capture the immunizations through a paper-based system; however, the remaining four sites encountered various obstacles that prevented capture of such data. Additional work will be required at these sites to overcome the barriers, which included privacy and confidentiality laws, time constraints brought on by the pandemic, as well as data quality concerns.

Inhaled corticosteroids are often used to manage chronic obstructive pulmonary disease, although the evidence regarding their long-term efficacy in preventing or reducing adverse health outcomes is not definitive. This retrospective cohort study analyzed whether regular inhaled corticosteroid use is associated with reduced health care utilization and all-cause mortality related to chronic obstructive pulmonary disease. Subjects were 2,902 health maintenance organization members aged 50 and over who met criteria for chronic obstructive pulmonary disease. The study used a composite endpoint of time to (1) death or (2) hospitalization or emergency room care related to chronic obstructive pulmonary disease, whichever occurred first, during a 4-year follow-up. Among the 42% of chronic obstructive pulmonary disease patients with an indication of co-morbid asthma, inhaled corticosteroid use was associated with significantly reduced risk for both all-cause mortality and the composite outcome. The reduction in risk was greatest in never- and ex-smokers. Among chronic obstructive pulmonary disease patients with no indication of asthma, inhaled corticosteroid use was associated with reduced risk only in never smokers. These findings generally persisted in separate analyses stratified by asthma status and in sensitivity analyses using four alternative definitions of regular medication use, with comparable results when regular medication use was treated as a fixed covariate defined at the start of follow-up. We conclude that use of inhaled corticosteroids was associated with reduced risk of chronic obstructive pulmonary disease exacerbations and all-cause mortality. This benefit was most pronounced among never-smokers and in those with evidence of co-morbid asthma.

Although pregnant women are a high-priority group for influenza vaccination, vaccination rates in this population remain below recommended levels. This prospective cohort study followed a group of pregnant women during the 2010-2011 influenza season to determine possible predictors of vaccination.Participants were 552 pregnant women who had not already received the influenza vaccine at the time of enrollment. Women completed a survey assessing knowledge, attitudes, and beliefs about vaccination (based on the Health Belief Model) by telephone and were then followed to determine vaccination status by the end of the 2010-2011 influenza season.Forty-six percent (n=252) of the women were vaccinated, and 54% (n=300) remained unvaccinated after enrollment in the study. Few baseline characteristics, with the exception of study site, month of enrollment, and maternal ethnicity, were predictive of vaccination status. Even after adjusting for significant baseline characteristics, we found that at least one item from each domain of the Health Beliefs Model was predictive of subsequent vaccination. Specifically, women who perceived they were susceptible to influenza, that they were at risk of getting seriously ill from influenza, that they would regret not getting vaccinated, and who trusted recommended guidelines about influenza vaccination during pregnancy were more likely to get vaccinated. Women who were concerned about vaccine side effects were less likely to get vaccinated.Trust in recommendations, perceived susceptibility to and seriousness of influenza, perceived regret about not getting vaccinated, and vaccine safety concerns predict vaccination in pregnant women.II.

Background Pregnant women are at greater risk of complications from influenza (flu) infection than the general population. Although vaccination is an effective method to prevent influenza, the vaccine is underutilized during pregnancy. A challenge to maternal flu vaccination is the paucity of data about the effectiveness of inactivated influenza vaccines (IIV) in preventing severe outcomes in pregnant women. To inform policy and address this knowledge gap, CDC developed a multi-country collaboration to investigate the preventive value of IIV during pregnancy during multiple flu seasons. We present the progress to date of this Network. Methods PREVENT was established in April 2016 to: i) estimate incidence of influenza and vaccination rates; ii) describe epidemiologic characteristics associated with illness; and iii) estimate IIV effectiveness in preventing hospitalizations during pregnancy associated with RT PCR -confirmed influenza. We selected sites that could identify the population of women known to be pregnant during flu seasons and integrate their hospitalization data, clinical laboratory testing, and vaccination records. We will assess VE using the case test-negative control design and use meta-analyses to pool VE estimates across sites and account for significant differences. Primary analyses will be completed by August 2017. Results Seven sites in Australia, Canada, Israel, and the US were selected; a protocol and data dictionary were finalized. We identified 1,024 pregnant women hospitalized with acute respiratory illness and RT-PCR tested, during six influenza seasons (2010–11 through 2015–16). Of the qualifying women, 550 (54%) tested positive for flu. Positivity varied by site (range 41% (US)–61.8% (Ontario, CAN)), and vaccination coverage varied across sites and seasons (range 7.3% (Ontario, CAN)–46% (US)). Analyses will examine flu season characteristics, vaccination patterns, and clinical and birth outcomes related to respiratory illness during pregnancy and flu incidence. Conclusion Laboratory-confirmed influenza hospitalization during pregnancy is a relatively low-frequency event. Pooling data across multiple sites offers a way to estimate VE against severe influenza outcomes in pregnant women that is informative to influenza vaccine policy. Disclosures A. Naleway, MedImmune: Investigator, Research grant; Pfizer: Investigator, Research grant; Merck: Investigator, Grant recipient; N. P. Klein, GSK: Investigator, Research grant; sanofi pasteur: Investigator, Grant recipient; Merck & Co: Investigator, Grant recipient; MedImmune: Investigator, Grant recipient; Protein Science: Investigator, Research grant; Pfizer: Investigator, Grant recipient; S. Irving, Medimmune/AstraZeneca: Investigator, Research support

We assessed the contribution of telephone medical care encounters to surveillance of adverse events (AE) following trivalent influenza vaccination in children age 6 months to 17 years. We used retrospective, self-controlled, case-series analysis to estimate adverse event incidence rate ratios for post-vaccination risk intervals relative to 15-28 days prior to vaccination. We confirmed possible vaccination reactions by medical record abstraction. Detection of 10 of 20 elevated incidence rate ratios required telephone data. We conclude that telephone encounters substantially contribute to the detection of possible influenza vaccination reactions, primarily local injection site and systemic reactions.

Background This study evaluated the utility of immunization registries in identifying vaccine refusals among children. Among refusers, we studied their socioeconomic characteristics and health care utilization patterns. Methods Medical records were reviewed to validate refusal status in the immunization registries of two health plans. Racial, education, and income characteristics of children claiming refusal were collected based on the census tract of each child. Health care utilization was identified using both electronic medical record and insurance claims. Within the immunization registries of two HMOs in the study, some providers use refusal and medical contraindication interchangeably, and some providers tend to always use "ever refusal." Therefore, we combined medical contraindication and refusal together and treated them all as "refusal" in this study. Results The immunization registry, compared to chart review, had negative predictive values of 85–92% and 90–97% for 2- and 6-year olds, and positive predictive values of only 52–74% and 59–62% to identify vaccine refusals. Refusers were more likely to reside in well-educated, higher income areas than non-refusers. Refusers had not opted out of health care system and continued, although less frequently for the age 2 and under group, to use services. Conclusion Without enhancements to immunization registries, identifying children with immunization refusal would be time consuming. Since communities where refusers live are well educated, interventions should target these communities to communicate vaccine adverse events and consequences of vaccine preventable diseases.