The impact of expanded adolescent vaccination against COVID-19 depends on the epidemic status: a mathematical modelling study
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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.
Highlights
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First study to compare the impact of expanding adolescent COVID-19 vaccination at two different epidemic points: one when a large epidemic is spreading and another at a more endemic stage of the epidemic.
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In autumn 2021, in the presence of the newly emerging Omicron variant, adolescent vaccination was necessary to curb infections in both the adolescent cohort and the overall population.
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Earlier implementation at sufficient coverage was more effective in reducing the number of infections at the peak of the Omicron wave, and getting ahead of the epidemic spread.
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In autumn 2022, when the Omicron epidemic was at an endemic stage, adolescent vaccination was not necessary to curb infections in both the adolescent cohort and the overall population.
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Our work shows that implementation, timing and speed of an adolescent immunisation programmes should be considered in conjunction with the epidemic status, incidence and prevalence of the epidemic at that time.
