Analyzing pre-pandemic patterns of contacts is partly inappropriate to explain the current COVID-19 situation in Germany

The National Academy of Sciences in Germany Leopoldina recently recommended to prepare a general vaccination mandate, to immediately reduce contacts in the private sector or to allow social life only to the vaccinated and recovered (“2G”) combined with private contact restrictions for the unvaccinated.¹ The reason is their claim that the unvaccinated are involved in 80% to 90% of new COVID-19 infections in Germany suggesting that only 10% to 20% of the vaccinated are involved in new cases. They refer to a pre-published mathematical simulation study entitled “Germany's current COVID-19 crisis is mainly driven by the unvaccinated”.² In this report the authors estimated for October 2021 that also the vaccinated are involved in 49% to 62% of the new COVID-19 cases which is omitted by the Leopoldina. In addition, the study authors describe that between 67% and 76% of the effective reproduction number was caused by unvaccinated individuals infecting vaccinated or other unvaccinated individuals. The calculation was done under specific assumptions. One of them is the type of contacts between age groups and subpopulation sizes. It was based on a dataset published in 2008 where leisure contacts accounted for approximately 20% of all contacts.³ The authors, however, did not consider that in October 2021 leisure contacts were not comparable for vaccinated and unvaccinated individuals. In many settings access was only allowed to the 2G population who could stay in full restaurants, crowded stadiums and concert halls. The unvaccinated, however, were often excluded from most of these settings. In addition, non-pharmaceutical measures such as face masks or physical distance were often not required for the 2G population in these crowded settings allowing a pre-pandemic behavior finally resulting in numerous outbreaks among the fully vaccinated. That is why the simulation model does not describe contacts in October 2021 in a realistic way and is at least for leisure contacts biased. A second concern is the application of an estimated average vaccine efficacy of 72% against symptomatic COVID-19 in adults as published by the Robert Koch-Institute.⁴ Population-based data from Sweden indicate that the vaccine effectiveness for preventing symptomatic COVID-19 is waning within a few months and has completely gone after four months (BNT162b2) or seven months (heterologous ChAdOx1 nCoV-19 / mRNA).⁵ Approximately 67% of the 261.735 breakthrough infections in Germany until the 25^th November 2021 was found after vaccination with BNT162b2. It is therefore plausible to assume that the real vaccine efficacy in October 2021 was lower than 72% also because 17.6% of the adult population in Germany finished their vaccination until May 2021 and 42.5% had partial immunization at that time. Overall, the simulated reality described in the pre-printed study by Maier et al. has some relevant limitations and should not be the scientific justification to recommend a general vaccination mandate and additional restrictions for the unvaccinated population.

Author contribution statement

GK as the sole author of this Letter, contributed to all aspects of the text.

Declaration of interest

The author has no competing interests to declare