Influenza Vaccine Effectiveness: Maintained Protection Throughout the Duration of Influenza Seasons 2010-2011 through 2013-2014
NAVAL HEALTH RESEARCH CENTER SAN DIEGO CA SAN DIEGO United States
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Factors, 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. Methods VE was assessed using febrile respiratory illness surveillance among Department of Defense non-active duty beneficiaries from influenza seasons 20102011 through 20132014. 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. Results This study included 1486 participants. We found an overall adjusted VE that provided significant and fairly consistent protection ranging from 54 to 67 during 0180 days postvaccination. This VE dropped to -11 95 confidence interval -102 to 39 during 181-365 days. Conclusions Our 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.