Germany's fourth COVID-19 wave was mainly driven by the unvaccinated

Benjamin F Maier; Marc Wiedermann; Angelique Burdinski; Pascal P Klamser; Mirjam A Jenny; Cornelia Betsch; Dirk Brockmann

doi:10.1038/s43856-022-00176-7

Germany's fourth COVID-19 wave was mainly driven by the unvaccinated

Commun Med (Lond). 2022 Sep 16:2:116. doi: 10.1038/s43856-022-00176-7. eCollection 2022.

Authors

Benjamin F Maier^{1

2}, Marc Wiedermann^{1

2}, Angelique Burdinski^{1

2}, Pascal P Klamser^{1

2}, Mirjam A Jenny^{3

4

5

6}, Cornelia Betsch^{3

6}, Dirk Brockmann¹

Affiliations

¹ Institute for Theoretical Biology and Integrated Research Institute for the Life-Sciences, Humboldt-University of Berlin, Philippstr. 13, 10115 Berlin, Germany.
² Robert Koch Institute, Nordufer 20, 13353 Berlin, Germany.
³ University of Erfurt, Nordhäuserstr. 63, 99089 Erfurt, Germany.
⁴ Harding Center for Risk Literacy, University of Potsdam, Virchowstrasse 2-4, 14482 Potsdam, Germany.
⁵ Max Planck Institute for Human Development, Lentzeallee 94, 14195 Berlin, Germany.
⁶ Bernhard-Nocht-Institut, Bernhard-Nocht-Straße 74, 20359 Hamburg, Germany.

Abstract

Background: While the majority of the German population was fully vaccinated at the time (about 65%), COVID-19 incidence started growing exponentially in October 2021 with about 41% of recorded new cases aged twelve or above being symptomatic breakthrough infections, presumably also contributing to the dynamics. So far, it remained elusive how significant this contribution was and whether targeted non-pharmaceutical interventions (NPIs) may have stopped the amplification of the crisis.

Methods: We develop and introduce a contribution matrix approach based on the next-generation matrix of a population-structured compartmental infectious disease model to derive contributions of respective inter- and intragroup infection pathways of unvaccinated and vaccinated subpopulations to the effective reproduction number and new infections, considering empirical data of vaccine efficacies against infection and transmission.

Results: Here we show that about 61%-76% of all new infections were caused by unvaccinated individuals and only 24%-39% were caused by the vaccinated. Furthermore, 32%-51% of new infections were likely caused by unvaccinated infecting other unvaccinated. Decreasing the transmissibility of the unvaccinated by, e. g. targeted NPIs, causes a steeper decrease in the effective reproduction number $R$ than decreasing the transmissibility of vaccinated individuals, potentially leading to temporary epidemic control. Reducing contacts between vaccinated and unvaccinated individuals serves to decrease $R$ in a similar manner as increasing vaccine uptake.

Conclusions: A minority of the German population-the unvaccinated-is assumed to have caused the majority of new infections in the fall of 2021 in Germany. Our results highlight the importance of combined measures, such as vaccination campaigns and targeted contact reductions to achieve temporary epidemic control.

Keywords: Computational biology and bioinformatics; Viral infection.