On temporal changes in the role of different age groups in propagating the Omicron epidemic waves in England

Background: There is limited information on the role of individuals in different age groups in the spread of infection during the Omicron epidemics, especially ones beyond the winter epidemic wave in 2021-2022. In England, booster vaccination against SARS-CoV-2 is currently restricted to persons aged over 50y and individuals in clinical risk groups. Methods: We used a previously developed methodology to evaluate the role of individuals in different age groups in propagating the Spring, Summer, and Autumn waves of the Omicron epidemic in England. This methodology utilizes the relative risk (RR) statistic that measures the change in the proportion of cases in each age group among all COVID-19 cases in the population before the peak of an epidemic wave vs. after the peak of an epidemic wave. Higher values for the RR statistic represent age groups that experienced a disproportionate depletion of susceptible individuals during the ascent of the epidemic (due to increased contact rates and/or susceptibility to infection). Results: For the 2022 Spring wave, the highest RR estimate belonged to children aged 5 to 9y (RR=2.05 (95%CI (2.02,2.08)), followed by children aged 10 to 14y (RR=1.68 (1.66,1.7)) and children aged 0 to 4y (RR=1.38 (1.36,1.41)). For the Summer wave, the highest RR estimates belonged to persons aged 20 to 34y: (RR=1.09 (1.07,1.12) in aged 20 to 24y, RR=1.09 (1.07,1.11) in aged 25 to 29y, RR=1.09(1.07,1.11) in aged 30 to 34y). For the Autumn wave, the highest RR estimate in adults belonged to those aged 70 to 74y (RR=1.10 (1.07,1.14)), followed by adults aged 35 to 39y (RR=1.09 (1.06,1.12)), adults aged 40 to 44y (RR=1.09 (1.06,1.12)), and adults aged 65 to 69y (RR=1.08 (1.05,1.11)) (with children excluded from the analyses due to limited/irregular detection of COVID-19 cases in children during the Autumn wave). Conclusions: As time progressed, ages of individuals who played the leading roles in propagating the Omicron epidemic waves in England shifted upward, with the leading roles in propagating COVID-19 epidemics in England currently belonging to adults of different ages. Extending booster vaccination to adults aged under 50y, and possibly to children should help limit the spread of Omicron infections in the community.