COVID-19 scenarios for comparing the effectiveness of age-specific vaccination regimes, exemplified for the city of Aschaffenburg (Germany)

Purpose of this report: The purpose of this rapid communication is to illustrate the effectiveness of different vaccination regimes for controlling the number of severe and critical COVID-19 cases in the city of Aschaffenburg, Germany. Our results show that, despite numerous vaccinations in the past, further vaccinations are necessary to immunize the population and to keep the number of severe and critical cases low in the coming months. Considering that not all people can or want to receive vaccination, we compare different age-specific vaccination approaches. Applied Methods: We use the agent-based epidemiological simulator Covasim for discussing the impact of different vaccination strategies. We calibrate it to reproduce the historical course of the COVID-19 pandemic in the city of Aschaffenburg, Germany; for this, we model and integrate numerous public health interventions imposed on the local population. As for some of the political actions rigorous quantification is currently not available, we fit those unknown (free) model parameters to published data on the measured epidemiological dynamics. Then we calculate the state of immunization of the population, gained through infections and vaccinations, at any time in the past, including models for time-dependent immunity decay that have been made available in Covasim. Finally, we define and compare scenar-ios of different vaccination regimes, especially with regard to vaccinating adolescents and providing booster vaccinations to the elderly. Key message: Without further vaccinations, we expect a strong increase in severe and critical cases. In order to restrict their growth our simulations suggest that in all considered cases vaccinations of unvaccinated people is more effective than booster vaccinations for already fully vaccinated people. This applies even to vaccinations of young people who are not themselves at high risk of developing severe or critical illness. We attribute this observation to the fact that immunization of adolescents indirectly protects vulnerable age groups by preventing the spread of the virus more ef-fectively than further immunizing other age groups. This indicates that with the pandemic ongoing, strategies focussed on minimizing individual health risks by vaccinations may no longer coincide with those needed to minimize the num-ber of severe and critical cases.