Influenza-like illness (ILI) outbreaks mainly occurred in
schools. And annually reformulated composition of influenza vaccines
makes it necessary to estimate the effectiveness of the seasonal
influenza vaccine. We aimed to estimate the effectiveness of the
seasonal influenza vaccine against influenza outbreaks in schools.
Methods This was a matched case-control study estimating the
effectiveness of the influenza vaccine in preventing school influenza
outbreaks. The laboratory-confirmed cases of influenza in school
children were paired by the random sample of asymptomatic classmates by
sex and age during the 2019–2020 influenza season. Influenza vaccine
effectiveness was estimated using a conditional logistic regression
model. Results During the 2019–2020 influenza season, 503 paired
samples of laboratory-confirmed influenza cases and asymptomatic
controls were enrolled. The influenza vaccination rates for cases and
controls were 0.40% and 1.59%, respectively. The vaccine effectiveness
against influenza outbreaks in schools was 74.35% (95% CI:
5.39–122.00) during the 2019–2020 season. Conclusions No significant
vaccine effectiveness was observed during influenza outbreaks in schools
during the 2019–2020 influenza season because of the low vaccination
rate. Efforts should be made to increase vaccination coverage among
students.
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