On the role of different age groups in propagating Omicron epidemics in France

Background: There is limited information on the role of different age groups in propagating SARSCoV2 epidemics driven by the Omicron variants. Methods: We examined the role of individuals in different age groups in propagating the Spring, Summer, and Autumn waves of the Omicron epidemics in France using the previously developed methodology based on the relative risk (RR) statistic that measures the change in the proportion of an age group among all cases admitted to ICU for COVID19 before vs. after the peak of an epidemic wave. Higher value of the RR statistic for a given age group suggests a disproportionate depletion of susceptible individuals in that age group during the ascent of the epidemic (due to increased contact rates and/or susceptibility to infection). Results: For the Spring wave (March 14 through May 15), the highest RR estimate belonged to children aged 10 to 19y (RR=1.92 (95% CI (1.18,3.12)), followed by adults aged 40 to 49y (RR=1.45 (1.09,1.93)) and children aged 0 to 9y (RR=1.31 (0.98,1.74)). For the Summer wave (June 27 through Aug. 21), the highest RR estimate belonged to children aged 0 to 9y (RR=1.61 (1.12,2.3)) followed by children aged 10 to 19y (RR=1.46 (0.72,2.93)) and adults aged 20 to 29y (RR=1.42 (0.91,2.23)). For the Autumn wave (Sep. 18 through Nov. 12), the highest RR estimate belonged to children aged 10 to 19y (RR=1.63 (0.72,3.71)), followed by adults aged 30 to 34y (RR=1.34 (0.8,2.25)) and 20 to 24y (RR=1.20 (0.65,2.21)). Conclusions: Children aged 10 to 19y played the greatest relative role in propagating Omicron epidemics, particularly when schools were open, followed by children aged 0 to 9y and adults aged 20 to 29y, as well as adults aged 30 to 49y. Persons aged over 50y played a more limited role in propagating Omicron infection in the community. Additional efforts are needed to increase vaccination coverage in children aged 10 to 19y, as well as younger children and young adults to mitigate Omicron epidemics in the community.