Rapid assessment of influenza vaccine effectiveness: analysis of an internet-based cohort

The effectiveness of influenza vaccination programmes is seldom known during an epidemic. We developed an internet-based system to record influenza-like symptoms and response to infection in a participating cohort. Using self-reports of influenza-like symptoms and of influenza vaccine history and uptake, we estimated vaccine effectiveness (VE) without the need for individuals to seek healthcare. We found that vaccination with the 2010 seasonal influenza vaccine was significantly protective against influenza-like illness (ILI) during the 2010-2011 influenza season (VE 52%, 95% CI 27-68). VE for individuals who received both the 2010 seasonal and 2009 pandemic influenza vaccines was 59% (95% CI 27-77), slightly higher than VE for those vaccinated in 2010 alone (VE 46%, 95% CI 9-68). Vaccinated individuals with ILI reported taking less time off work than unvaccinated individuals with ILI (3.4 days vs. 5.3 days, P<0.001).     

Influenza vaccine effectiveness: Maintained protection throughout the duration of influenza seasons 2010–2011 through 2013–2014

BackgroundFactors, such as age, comorbidities, vaccine type, herd immunity, previous influenza exposure, and antigenic shift may impact the immune response to the influenza vaccine, protection against circulating strains, and antibody waning. Evaluating vaccine effectiveness (VE) is important for informing timing of vaccine administration and evaluating overall vaccine benefit.MethodsVE was assessed using febrile respiratory illness surveillance among Department of Defense non-active duty beneficiaries from influenza seasons 2010–2011 through 2013–2014. Respiratory specimens were taken from participants meeting the case definition and tested by polymerase chain reaction for influenza. VE was calculated using logistic regression and by taking 1 minus the odds ratio of being vaccinated in the laboratory confirmed positive influenza cases versus laboratory confirmed negative controls.ResultsThis study included 1486 participants. We found an overall adjusted VE that provided significant and fairly consistent protection ranging from 54% to 67% during 0–180 days postvaccination. This VE dropped to −11% (95% confidence interval: −102% to 39%) during 181–365 days.ConclusionsOur study found moderate VE up to 6 months postvaccination. Since the influenza season starts at different times each year, optimal timing is difficult to predict. Consequently, early influenza vaccination may still offer the best overall protection.     

Coverage rates of influenza vaccine in Italy during the 2002/3 and 2003/04 seasons: a cross-sectional study

The objective of this survey was to assess the level of influenza vaccination coverage in the season 2002/ 2003 compared with the season 2003/2004 in Italy, to understand the drivers and barriers to vaccination and to determine the intention for vaccination for the following winter. We conducted a random-sampling, telephone-based household survey among non-institutionalised individuals representative of the population aged 14 years and above. The surveys for 2002/2003 and 2003/2004 used the same questionnaire and were subsequently pooled. Four target groups were determined for analysis: (1) persons aged 65 years and above; (2) people working in the medical field; (3) persons suffering from a chronic illness and (4) all other groups. The overall sample consisted of 4010 people. The influenza vaccination coverage rate in Italy increased from 19.6% in season 2002/2003 to 22.2% in season 2003/2004. The most frequent reasons mentioned by vaccinees to get vaccinated were advice received from the family doctor or nurse (48.9%), influenza being considered a serious illness which people did not want to contract (38.5%) and not wanting to pass the influenza bug to family and friends (29.2%). Reasons mentioned by never vaccinated people for not getting vaccinated were the fact that people did not consider it before (34.9%), the opinion that one was not very likely to catch influenza (32.2%) and influenza not being a serious illness (23.4%). Options encouraging an influenza vaccination are a recommendation by the family doctor or nurse (58.4%), more available information on the vaccine regarding efficacy and tolerance (34.4%) and more available information on the disease (24.3%). We therefore suggest that family doctors be better informed on influenza vaccine and the disease itself in order to enable them to actively inform their patients on these topics accordingly.     

Methodologic issues regarding the use of three observational study designs to assess influenza vaccine effectiveness

BACKGROUND: Influenza causes substantial morbidity and annual vaccination is the most important prevention strategy. Accurately measuring vaccine effectiveness (VE) is difficult. The clinical syndrome most closely associated with influenza virus infection, influenza-like illness (ILI), is not specific. In addition, laboratory confirmation is infrequently done, and available rapid diagnostic tests are imperfect. The objective of this study was to estimate the joint impact of rapid diagnostic test sensitivity and specificity on VE for three types of study designs: a cohort study, a traditional case-control study, and a case-control study that used as controls individuals with ILI who tested negative for influenza virus infection. METHODS: We developed a mathematical model with five input parameters: true VE, attack rates (ARs) of influenza-ILI and non-influenza-ILI and the sensitivity and specificity of the diagnostic test. RESULTS: With imperfect specificity, estimates from all three designs tended to underestimate true VE, but were similar except if fairly extreme inputs were used. Only if test specificity was 95% or more or if influenza attack rates doubled that of background illness did the case-control method slightly overestimate VE. The case-control method usually produced the highest and most accurate estimates, followed by the test-negative design. The bias toward underestimating true VE introduced by low test specificity increased as the AR of influenza- relative to non-influenza-ILI decreases and, to a lesser degree, with lower test sensitivity. CONCLUSIONS: Demonstration of a high influenza VE using tests with imperfect sensitivity and specificity should provide reassurance that the program has been effective in reducing influenza illnesses, assuming adequate control of confounding factors.     

Effectiveness of repeated influenza vaccination among the elderly population with high annual vaccine uptake rates during the three consecutive A/H3N2 epidemics

BackgroundAnnually, about 80% of the Korean elderly aged ≥65 years receive influenza vaccination. Repeated annual vaccination has been suggested as an important factor of poor influenza vaccine effectiveness (VE), though reported conflicting results.MethodsDuring the consecutive A/H3N2-dominant influenza seasons between 2012 and 2015, we comparatively evaluated the VE (repeated vs. current season only) against laboratory-confirmed influenza, pneumonia and hospitalization in the elderly aged ≥65 years with influenza-like illness (ILI). Clinical and demographic data were collected prospectively, and vaccination status of prior and current seasons was verified using the immunization registry data of Korean Centers for Disease Control and Prevention.ResultsDuring the first A/H3N2-dominant season in 2012–2013, influenza vaccine showed statistically significant effectiveness against influenza A infection only and when vaccinated in the current season only (VE 53%, 95% CI 15–77). In the latter two seasons (2013–2015 years), the adjusted VE for influenza A was indistinguishable between repeated vaccination and vaccination in the current season only.ConclusionDuring consecutive influenza A/H3N2 epidemics, poor influenza vaccine effectiveness may be more pronounced among the elderly population with a high annual vaccine uptake rate.     

2013-2014年度季节性流行性感冒疫苗对儿童保护效果的病例对照研究

目的 评价2013-2014年度季节性流行性感冒疫苗（流感疫苗）对6~59月龄儿童的保护效果。方法 选择2013-2014年度6~59月龄的实验室诊断流感病例为病例组,在广州市免疫规划系统中随机选择健康儿童为对照组,进行成组病例对照研究,采用非条件Logistic回归计算保护效果。结果 本研究共纳入2 690名研究对象。2013-2014年度,流感疫苗对6~59月龄儿童的保护效果为42.3%（95% CI:27.8%~53.8%）,对36~59月龄儿童的保护效果高于6~35月龄儿童,完全免疫的保护效果高于部分免疫,性别间保护效果无统计学差异。结论 流感疫苗对6~59月龄儿童具有中等保护效果,建议6~59月龄儿童每年接种流感疫苗。     

Seasonal influenza vaccine effectiveness against medically attended influenza illness among children aged 6–59 months,October 2011–September 2012: A matched test-negative case–control study in Suzhou,China

BackgroundSeasonal influenza infections among young children in China lead to substantial numbers of hospitalizations and financial burden. This study assessed the seasonal influenza vaccine effectiveness (VE) against laboratory confirmed medically attended influenza illness among children in Suzhou, China, from October 2011–September 2012.MethodsWe conducted a test-negative case–control study among children aged 6–59 months who sought care at Soochow University Affiliated Children's Hospital (SCH) from October 2011–September 2012. A case was defined as a child with influenza-like illness (ILI) or severe acute respiratory infection (SARI) with an influenza-positive nasopharyngeal swab by rRT-PCR. Controls were selected from children presenting with ILI or SARI without laboratory confirmed influenza. We conducted 1:1 matching by age and admission date. Vaccination status was verified from the citywide immunization system database. VE was calculated with conditional logistic regression: (1 − OR) × 100%.ResultDuring the study period, 2634 children aged 6–59 months presented to SCH with ILI (1975) or SARI (659) and were tested for influenza. The vaccination records were available for 69% (1829; ILI: 1354, SARI: 475). Among those, 23% (427) tested positive for influenza, and were included as cases. Among influenza positive cases, the vaccination rates were 3.2% for SARI and 4.5% for ILI. Among controls, the vaccination rates were 13% for SARI, and 11% for ILI. The overall VE against lab-confirmed medically attended influenza virus infection was 67% (95% CI: 41–82). The VE for SARI was 75% (95% CI: 11–93) and for ILI was 64% (95% CI: 31–82).ConclusionsThe seasonal influenza vaccine was effective against medically attended lab-confirmed influenza infection in children aged 6–59 months in Suzhou, China in the 2011–12 influenza season. Increasing seasonal influenza vaccination among young children in Suzhou may decrease medically attended influenza-associated ILI and SARI cases in this population.     

Exploring the reasons for low pertussis vaccine effectiveness in Ontario,Canada, 2006–2008: a Canadian Immunization Research Network study

ObjectivesAlthough pertussis vaccines have been widely used for many decades, a burden of illness persists. Resurgences in Ontario, Canada, have not been substantial in the past decade, but an outbreak of pertussis occurred in Toronto between 1 October 2005 and 31 March 2006. Previous Ontario studies found high vaccine effectiveness (VE) in the initial years post-immunization. In order to explore the impact of outbreaks and external factors on VE, we investigated pertussis VE during the period 2006–2008.MethodsWe assessed pertussis VE using a frequency-matched case-control study for the period 1 March 2006 to 31 December 2008. We used logistic regression to estimate VE by age, time since last vaccination, and vaccination status according to the Ontario recommended schedule. We compared analyses including and excluding cases from Toronto, and to two recent Ontario pertussis VE studies.ResultsWe included 1797 confirmed cases and 7188 matched controls. Most cases were under 4 years of age during the study period. Pertussis VE was 3.8% (95% CI: − 21.0, 24.0) in the period 15–364 days following the last pertussis vaccine dose, and increased with increasing time since vaccination. Pertussis VE in the first 15–364 days excluding Toronto increased to 57.1% (95% CI: 26.0, 75.1), but the trend of increasing VE with time since vaccination persisted. Although VE was higher in older (6–11 years) than younger (0–5 years) children, it was lower at 12–13 years than after 14 years.ConclusionVE was lower in comparison with other studies conducted in Ontario, particularly in younger children. Various factors occurring during the study period may have influenced the results, including clinical testing of asymptomatic contacts, laboratory testing and methods and reporting practice, and a sensitive case definition. Further studies are needed to optimize methods for measuring VE to inform pertussis vaccine policy.     

2017－2018年流感流行季儿童接种流感疫苗效果社区队列研究

目的 评价6~72月龄儿童接种流感疫苗效果。方法 采用社区队列研究设计,2017年10-12月,从浙江省永康和义乌两市10家儿童接种门诊招募了1 752名6~72月龄儿童。每名儿童入队列后,完成知情同意和问卷调查,并随访至2018年4月30日,观察记录流感样病例（ILI）发病、门诊就诊和自行服药及流感疫苗接种情况。以ILI、门诊就诊和自行服药的发生次数为因变量,采用广义线性模型（GLM）拟合,估算流感疫苗效果（VE）值。结果 1 752名儿童中,男童925名（52.80%）,月龄M=30.00月,累计随访观察308 166人天,平均每天有5.27‰发生ILI、3.41‰因ILI去医院门诊就诊、1.45‰因ILI自行服药治疗;共有643名儿童接种了流感疫苗,与未接种儿童相比,流感疫苗对ILI、门诊就诊和自行服药的VE值分别为23.5%（95% CI：15.1%~31.1%）、19.3%（95% CI：8.2%~29.1%）和25.8%（95% CI：9.3%~39.3%）。643名接种儿童,接种后与接种前比,流感疫苗针对36~72月龄儿童ILI、门诊就诊和自行服药的VE值分别为31.9%（95% CI：12.7%~46.9%）、32.6%（95% CI：8.6%~50.3%）和44.3%（95% CI：11.9%~64.8%）,而对6~35月龄儿童,VE值均无统计学意义。2016-2018年流感疫苗不同接种暴露VE值评估,两个流感流行季均有接种史的,仅2017-2018年流感流行季有接种史的,流感疫苗VE值,均有统计学意义;仅2016-2017年流感流行季有接种史的,VE值均无统计学意义。结论 流感流行季接种流感疫苗一定程度可预防ILI发病、门诊就诊和自行服药,且对36~72月龄儿童保护效果优于6~35月龄儿童。     

Effectiveness of an acellular pertussis vaccine in Japanese children during a non-epidemic period: a matched case-control study

The number of pertussis cases in Japan has decreased dramatically following the nationwide use of an acellular pertussis vaccine combined with diphtheria-tetanus toxoids (DTaP vaccines) which began in 1981. However, the effectiveness of the DTaP vaccine has not been systematically evaluated using appropriate epidemiological methods during a non-epidemic period in Japan. We evaluated the vaccine effectiveness (VE) of the Kaketsuken DTaP vaccine which contains two-component pertussis antigens in Japanese children from 1999 to 2001 using a matched case-control design and data from the Basic Resident Registration and Maternal and Child Health Handbooks. The DTaP vaccination history of 15 children with pertussis and 59 controls was obtained. The VE of 3 or 4 pertussis vaccinations compared with non-vaccination (baseline) was 96.9% for coughing attacks that lasted 7 days, 96.4% for those lasting 14 days, and 95.9% for those lasting 21 days. These findings suggest that DTaP vaccination effectively prevented pertussis during a non-epidemic period in Japan.     

Effectiveness of the 2011–12 Influenza Vaccine: Data from US Military Dependents and US-Mexico Border Civilians

Objective

To assess effectiveness of the influenza vaccine among US military dependents and US-Mexico Border populations during the 2011–12 influenza season.

Introduction

As a result of antigenic drift of the influenza viruses, the composition of the influenza vaccine is updated yearly to match circulating strains. Consequently, there is need to assess the effectiveness of the influenza vaccine (VE) on a yearly basis. Ongoing febrile respiratory illness (FRI) surveillance captures data and specimens that are leveraged to estimate influenza VE on an annual basis.

Methods

Data from ongoing FRI surveillance at US Military and US-Mexico border clinics were used to estimate VE. We conducted a case–control study between weeks 3 and 17 of the 2011–12 influenza season. Specimens were collected from individuals meeting FRI case definition (fever ≥ 100.0 F with either cough or sore throat). Cases were laboratory confirmed influenza infection and controls were negative for influenza. Interviewer-administered questionnaires collected information on patient demographics and clinical factors and vaccination status. Logistic regression was used to calculate the crude and adjusted odds ratios (OR) and VE was computed as (1-OR) × 100%. Vaccine protection was assumed to begin 14 days post-vaccination.

Results

A total of 155 influenza positive cases and 429 influenza negative controls were included in the analysis - 72 cases were influenza A(H3N2), 38 cases were influenza A(H1N1), and 45 cases were influenza B. Overall adjusted VE against laboratory-confirmed influenza was 46% (95% CI, 19–64%); unadjusted was 39% (95% CI, 11–58%). Influenza subtype analyses revealed moderate protection against A/H3 and A/H1 and lower protection against B. Lowest estimated VE was seen in older individuals, age 65 and older.

Conclusions

Influenza vaccination was moderately protective against laboratory confirmed influenza in this population. Continued surveillance is important in monitoring the effectiveness of the influenza vaccine.     

Deaths following influenza vaccination--background mortality or causal connection?

In October 2006, four deaths occurred in Israel shortly after influenza immunization, resulting in a temporary halt to the vaccination campaign. After an epidemiologic investigation, the Ministry of Health concluded that these deaths were not related to the vaccine itself and the campaign resumed; however, vaccine uptake was markedly reduced. Estimates of true background mortality in this high-risk population would aid in public education and quell unnecessary concerns regarding vaccine safety. We used data from a large HMO to estimate mortality in influenza vaccine recipients aged 55 and over during four consecutive winters (2003, 2004, 2005 and 2006). Date of immunization was ascertained from patient treatment files, vital status through Israeli National Insurance Institute data. We calculated crude death rates within 7, 14 and 30 days of influenza immunization, and used a Cox Proportional Hazards Model to estimate the risk of death within 14 days of vaccination, adjusting for age and comorbid conditions (age over 75, history of diabetes or cardiovascular disease, status as homebound patient) in 2006. The death rate among influenza vaccine recipients ranged from 0.01 to 0.02% within 7 days and 0.09-0.10% at 30 days. Influenza immunization was associated with a decreased risk of death within 14 days after adjustment for comorbidities (Hazard ratio, 0.33, 95% CI, 0.18-0.61). Our findings support the assumption that influenza vaccination is not associated with increased risk of death in the short term.     

Estimating influenza vaccine efficacy from challenge and community-based study data

In this paper, the authors provide estimates of 4 measures of vaccine efficacy for live, attenuated and inactivated influenza vaccine based on secondary analysis of 5 experimental influenza challenge studies in seronegative adults and community-based vaccine trials. The 4 vaccine efficacy measures are for susceptibility (VE(S)), symptomatic illness given infection (VE(P)), infection and illness (VE(SP)), and infectiousness (VE(I)). The authors also propose a combined (VE(C)) measure of the reduction in transmission in the entire population based on all of the above efficacy measures. Live influenza vaccine and inactivated vaccine provided similar protection against laboratory-confirmed infection (for live vaccine: VE(S) = 41%, 95% confidence interval (CI): 15, 66; for inactivated vaccine: VE(S) = 43%, 95% CI: 8, 79). Live vaccine had a higher efficacy for illness given infection (VE(P) = 67%, 95% CI: 24, 100) than inactivated vaccine (VE(P) = 29%, 95% CI: -19, 76), although the difference was not statistically significant. VE(SP) for the live vaccine was higher than for the inactivated vaccine. VE(I) estimates were particularly low for these influenza vaccines. VE(SP) and VE(C) can remain high for both vaccines, even when VE(I) is relatively low, as long as the other 2 measures of vaccine efficacy are relatively high.     

Inactivated influenza vaccine effectiveness and an analysis of repeated vaccination for children during the 2016/17 season

ObjectivesWe assessed the vaccine effectiveness (VE) of inactivated influenza vaccine (IIV) in children 6 months to 15 years of age during the 2016/17 season. In addition, we estimated the impact of repeated vaccination in children on VE.MethodsOur study for VEs in preventing influenza and admission due to influenza were conducted according to a test-negative case-control design (TNCC) based on influenza rapid diagnostic test results. We also analyzed the VE by vaccine status in the current and previous seasons for the impact of repeated vaccination.ResultsDuring the 2016/17 season, the quadrivalent IIV was used in Japan. The adjusted VE in preventing influenza illness was 38% (95% CI, 29–46) against influenza A and 39% (95% CI, 18–54) against influenza B. Infants showed no significant VE. The VE in preventing hospitalization was not demonstrated. For the analysis of repeated vaccination, the vaccine was effective only when immunization occurred in the current season. The children who were immunized in two consecutive seasons were more likely to develop influenza compared to those immunized in the current season only (odds ratio, 1.58 [95% CI, 1.05–2.38], adjusted odds ratio, 1.53 [95% CI, 0.99–2.35]). However, the odds ratio of repeated vaccination was not significant when the analysis excluded those who developed influenza in the previous season.ConclusionsVE in children in the 2016/17 season was similar to values previously reported. Repeated vaccination interfered with the VE against any influenza infection in the 2016/17 season. The results of our study suggest that decreased VE by repeat vaccination phenomenon was associated with immunity by influenza infection in the previous season. However, the influenza vaccine should be recommended every season for children.     

Effectiveness of virosomal subunit influenza vaccine in preventing influenza-related illnesses and its social and economic consequences in children aged 3-14 years: a prospective cohort study

To evaluate the effectiveness of a virosomal subunit influenza vaccine in preventing influenza-related illnesses and its social and economic consequences in children aged 3-14 years, a prospective cohort study was carried out during the 2004-2005 influenza season in 11 private pediatric clinics in the Barcelona metropolitan area. One dose of a virosomal subunit inactivated influenza vaccine (Inflexal V Berna) was given during September and October 2004 to healthy children aged 3-14 years attended in 5 of the 11 clinics. Who comprised the vaccinated cohort (n=966). The non-vaccinated cohort (n=985) was comprised of children attended in the other six clinics. Informed consent was obtained from all parents. The follow up was performed between 1 November 2004 and 31 March 2005. Using a self-administered questionnaire, information was collected from parents or guardians on any type of acute, febrile respiratory illness suffered by their children during the study period, including antibiotic use, and absence from school or work-loss of parents as a result of the illness. RT-PCR (influenza A+B+C) was carried out on pharyngeal and nasal samples obtained from children attended by pediatricians during this period in these clinics with the following symptoms: fever> or =38.5 degrees lasting at least 72h, cough or sore throat (influenza-like illness). Adjusted vaccination effectiveness was 58.6% (95% CI 49.2-66.3) in preventing acute febrile respiratory illnesses, 75.1% (95% CI 61.0-84.1) in preventing cases of influenza-like illnesses and 88.4% (95% CI 49.2-97.3) in preventing laboratory-confirmed cases of influenza A. The adjusted vaccination effectiveness in reducing antibiotic use (18.6%, 95% CI -4.2 to 3.64), absence from school (57.8%, 95% CI 47.9-65.9) and work-loss of parents (33.3%, 95% CI 8.9-51.2) in children affected by an acute febrile respiratory illness was somewhat lower. Vaccination of children aged 3-14 years in pediatric practices with one dose of virosomal subunit inactivated influenza vaccine has the potential to considerably reduce the health and social burdens caused by influenza-related illnesses.     

Effectiveness of pandemic and seasonal influenza vaccines in preventing pandemic influenza-associated hospitalization

Vaccines are leading pharmacological measures for limiting the impact of pandemic influenza in the community. The objective of this study was to investigate the effectiveness of influenza (pandemic and seasonal) vaccines in preventing pandemic influenza-associated hospitalization. We conducted a multicenter matched case-control study in 36 Spanish hospitals. Patients hospitalized with confirmed pandemic influenza between November 2009 and February 2010 and two hospitalized controls per case, matched according to age, date of hospitalization and province of residence, were selected. Multivariate analysis was performed using conditional logistic regression. Subjects were considered vaccinated if they had received the vaccine >14 days (seasonal influenza vaccine) or >7 days (pandemic influenza vaccine) before the onset of symptoms (cases) or the onset of symptoms of the matched case (controls). For the pandemic influenza vaccine, vaccination effectiveness (VE) was estimated taking into account only patients recruited from November 23, 2009, seven days after the beginning of the pandemic influenza vaccination campaign. 638 cases and 1250 controls were included. The adjusted VE of the pandemic vaccine in the ≥18 years age group was 74.2% (95% CI, 29-90) and that of the influenza seasonal vaccine 15.0% (-34 to 43). The recommendation of influenza vaccination should be reinforced as a regular measure to reduce influenza-associated hospitalization during pandemics and seasonal epidemics.     

Can routinely collected laboratory and health administrative data be used to assess influenza vaccine effectiveness? Assessing the validity of the Flu and Other Respiratory Viruses Research (FOREVER) Cohort

BackgroundLinking data on laboratory specimens collected during clinical practice with health administrative data permits highly powered vaccine effectiveness (VE) studies to be conducted at relatively low cost, but bias from using convenience samples is a concern. We evaluated the validity of using such data for estimating VE.MethodsWe created the Flu and Other Respiratory Viruses Research (FOREVER) Cohort by linking individual-level data on respiratory virus laboratory tests, hospitalizations, emergency department visits, and physician services. For community-dwelling adults aged > 65 years, we assessed the presence and magnitude of information and selection biases, generated VE estimates under various conditions, and compared our VE estimates with those from other studies.ResultsWe included 65,648 unique testing episodes obtained from 54,434 individuals during the 2010–11 to 2015–16 influenza seasons. To examine information bias, we found the proportion testing positive for influenza for patients with unknown interval from illness onset to specimen collection was more similar to patients for whom illness onset date was ≤ 7 days before specimen collection than to patients for whom illness onset was > 7 days before specimen collection. To assess the presence of selection bias, we found the likelihood of influenza testing was comparable between vaccinated and unvaccinated individuals, although the adjusted odds ratios were significantly greater than 1 for some healthcare settings and during some influenza seasons. Over 6 seasons, VE estimates ranged between 36% (95%CI, 27–44%) in 2010–11 and 5% (95%CI, –2, 11%) in 2014–15. VE estimates were similar under a range of conditions, but were consistently higher when accounting for misclassification of vaccination status through a quantitative sensitivity analysis. VE estimates from the FOREVER Cohort were comparable to those from other studies.ConclusionsRoutinely collected laboratory and health administrative data contained in the FOREVER Cohort can be used to estimate influenza VE in community-dwelling older adults.