Effectiveness of inactivated quadrivalent influenza vaccine in the 2015/2016 season as assessed in both a test-negative case-control study design and a traditional case-control study design
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Both traditional case-control studies (TCCSs) and test-negative case-control studies (TNCCSs) are commonly used to assess influenza vaccine effectiveness (VE). To compensate for the fact that observational studies are susceptible to bias, we combined both methods to assess VE in one geographical area during the 2015/2016 season, when influenza A (H1N1)pdm was dominant. Our TNCCS covered 331 children aged 6 months to 15 years who visited our hospital with fever, including 182 with influenza, and our TCCS covered 812 pediatric outpatients aged 6 months to 15 years, including 214 with influenza. Influenza infection and vaccination history were reviewed, and VE was calculated as (1 − odds ratio) × 100. In the TNCCS, VE against influenza A was 68% (95% CI 47–81) overall, and 70% (48–83) for those given two doses; against influenza B, VE was 37% (− 12–64) overall and 49% (2–74) for two doses. In the TCCS, VE against influenza A was 44% (15–63) overall and 44% (13–64) for two doses, and VE against influenza B was 24% (− 19–52) overall and 41% (3–64) for two doses.
What is Known:
• Influenza vaccine effectiveness (VE) varies from year to year.
• Observational studies are conventionally used for VE assessment. However, they are inherently susceptible to bias and confounding.
What is New:
• This is the first report of influenza VE assessment using more than one observational study and performed in a specific area during the same season.
• VE estimates obtained in our traditional case-control study were lower than those in our test-negative case-control study, but both studies found significant VE against influenza.
KeywordsInfluenza vaccine effectiveness Inactivated quadrivalent influenza vaccine 2015/2016 season Test-negative case-control study Traditional case-control study
Traditional case-control study
Test-negative case-control study
T.K., M.S., S.S., and N.S. designed the study. T.K., M.A., and H.T. collected and analyzed data. T.K., M.S., M.A., and S.S wrote the manuscript. N.S. and T.T. critically reviewed the manuscript. All authors read and approved the final manuscript.
This work was supported by a grant for medical research from Tokyo Metropolitan Government.
Compliance with ethical standards
Conflict of interest
This work was supported by a grant for medical research from Tokyo Metropolitan Government. Author Norio Sugaya has received lecture fees from Astellas, Daiichi Sankyo, Denka Seiken, and Takeda, but none of these talks were connected with the work presented here. Author Masayoshi Shinjoh has also received lecture fees from Japan Vaccine and MSD, but again, the talks were unconnected with the studies describe in this paper. No other authors declare any potential conflicts of interest.
Informed consent was obtained from all individual participants included in the study.
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