Impact of booster vaccination on the control of COVID-19 in the context of waning immunity: Application to France in the autumn-winter 2021-2022

Europe is confronted with a large COVID-19 wave caused by the Delta variant in autumnwinter 2021-2022. Using a mathematical model applied to Metropolitan France, we find that the hospitalisation peak might be reduced by 25%, 36% and 43% if boosters are administered to those aged 65+, 50+ or 18+, respectively, with a delay of 5 months between the second and third dose. Ten percent reduction in transmission rates might further reduce peak size by 41%, indicating that even small increases in protective behaviours may play a critical role to mitigate the wave.Most European countries have experienced an important rise in SARS-CoV-2 infections and hospitalisations in the Autumn 2021. In response to this resurgence and to the reported partial decay of immunity, countries have started administering vaccine booster doses, relying on different eligibility criteria. Here, we present modelling analyses assessing different administration strategies for booster doses that informed the recommendations of the French National Immunization Technical Advisory Group (Haute Autorité de Santé) in the context of Metropolitan France.