Estimating the effect of self-protection on transmission dynamics of SARS-CoV-2 in Germany in 2021: A modelling study

Background During the COVID-19 pandemic, German states implemented non pharmaceutical interventions, while individuals also adopted self-initiated protective behavior. Most epidemiological studies tend to focus on one of these aspects, but in reality, both factors influence transmission dynamics simultane ously. In this study, we investigate the effect of self-protection and NPIs on the transmission dynamics of SARS-CoV-2 in Germany during 2021 and identify the corresponding model parameters based on publicly available data. Methods We present a mathematical model that integrates both self-initiated protective behavior and mandated policies. By using infection and intensive care unit data from four German states, we identify all behavioral and some viral parameters, while some are set according to literature values. Since the data alone do not reveal the cause of reduction, we use the different functional structures of self29 protection and non-pharmaceutical interventions to determine their respective influence. Based on these parameters, we conduct counterfactual simulations, modeling the absence of one of the mechanisms, respectively. Results Our findings indicate that both mechanisms substantially reduced transmission. Self-protection re duced the transmission less than mandated policies most of the time, but provided between 67.6 (± 0.69) % and 81.9 (± 0.21) % further reduction of the critical contact rate at highest reported values of intensive care unit occupancy. Through counterfactual simulations, we demonstrate that the absence of policies or self-protection would have resulted in higher case numbers or the need for stronger adaptations. Conclusion The results emphasize the crucial role of self-protection in addition to mandated policies in controlling the spread of the virus. Our research high42 lights the importance of incorporating self-protective behavior in epidemiological models, which are used for policy evaluation.