Abstract
A test-negative design study with different control groups (influenza test-negative controls, non-influenza virus positive controls, and pan-negative controls) was conducted to assess inactivated influenza vaccine effectiveness (VE) in adults aged ≥18 years, 2016–2017 through 2019–2020 influenza seasons. A database was developed from the US Department of Defense Global Respiratory Pathogen Surveillance Program. VE was estimated using a generalized linear mixed model with logit link and binomial distribution, adjusted for confounding effects. A total of 7114 adults including 2543 medically attended, laboratory-confirmed influenza-positive cases were identified. Using influenza test-negative controls, the adjusted VE in adults was 40% [95% confidence interval (CI): 33–46%] overall, including 46% (95% CI: 36–55%) for influenza A(H1N1)pdm09, 32% (95% CI: 19–42%) for influenza A(H3N2), and 54% (95% CI: 44–62%) for influenza B. The age-stratified analysis showed that VE estimates against influenza A(H1N1)pdm09 (34%; 95% CI: −29–66%) and influenza A(H3N2) (6%; 95% CI: −60–45%) were low and non-significant for elderly adults ≥65 years of age. Overall VE estimates against any influenza or by influenza (sub)types in adults were consistent when using influenza test-negative controls, non-influenza virus positive controls, and pan-negative controls. Inactivated influenza vaccination provided moderate protection against influenza virus infection, based on the analysis from a large number of adults aged ≥18 years over multiple influenza seasons.
Highlights
Seasonal influenza primarily causes human respiratory disease in all ages
Our findings clearly demonstrated inactivated influenza vaccine was less effective against influenza A(H1N1)pdm09 and influenza A(H3N2) in adults aged ≥65 years
We found the vaccine effectiveness (VE) against influenza A(H3N2) was lower in adults aged 50–64 years than in adults aged 18–49 years
Summary
Seasonal influenza primarily causes human respiratory disease in all ages. Elderly adults (≥65 years of age) are at high risk of influenza virus infection and severe influenza-related complications including hospitalization and death [1]. Influenza vaccination is considered the most effective measure available to protect against influenza viruses, combat influenza virus infection and lessen disease severity. The Department of Defense (DoD) Global Respiratory Pathogen Surveillance (DoDGRS) Program performs routine respiratory pathogen surveillance among DoD service members and their beneficiaries, allowing annual estimates of influenza vaccine effectiveness (VE) [2,3,4,5]. Annual estimates of VE are necessary as the circulating influenza viruses differ from year to year. Due to the small sample size, it might not be possible to accurately estimate
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