Considering the unpreceded situation linked to the COVID-19 pandemic and the associated stringent measures and non-pharmaceutical interventions in place to address the public health crisis, the circulation of non-COVID-19 respiratory viruses (including influenza) was very limited during the 2020-21 influenza season, phenomenon that has been well described in Europe.
Consequently, conversely to previous seasons, DRIVE faced challenges during the season 2020/21 to identify influenza cases and to collect necessary data for influenza vaccines effectiveness (IVE) analysis. The number of influenza positive cases reported in DRIVE was extremely low and did not allow to perform the Test Negative Design pooled analysis to estimate brand specific IVE. IVE estimates were calculated for the population aged 65 years and above from the Finnish register-based cohort study but confidence intervals were too wide to draw any conclusion.
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