The impact of expanded adolescent vaccination against COVID-19 depends on the epidemic status: a mathematical modelling study

Background/Objectives We evaluated the impact of the COVID-19 adolescent vaccination in England at two different epidemic points: the autumn (August-November) 2021, in the presence of a large Omicron epidemic wave, and the autumn (August-November) 2022, when the subsequent Omicron epidemic was at an endemic stage. Methods Using the Covasim SARS-CoV-2 model for England, under varying vaccine uptake and onset time, we evaluated the impact of a)vaccinating 18+ only versus additional 12+ vaccination from the autumn 2021; and b)the current immunisation strategy at the time versus additional 12+ vaccination from September 2022, projecting the number of new daily SARS-CoV-2 infections, hospitalisations and deaths. Results In presence of the BA.1 Omicron wave in late 2021, the expanded adolescent vaccination averted ~3,000,000 cases across all-ages, ~1,010,000 SARS-CoV-2 infections in the period 2-6 months from vaccine onset in the vaccinated cohort. During the Omicron waves in 2022, additional adolescents vaccination did not significantly reduce the COVID-19 burden in the entire population, nor within the vaccinated cohort. Conclusions Our findings highlight that adolescent vaccination impact depends on the timing/speed of implementation, other present intervention strategies, and the status of the epidemic at the time and it should not be considered as a stand-alone immunisation strategy.