Face masks considerably contribute to reducing the spread of coronavirus infections

Researchers compare the growth of infection rates in Jena with those of similar cities where wearing of face masks was not made compulsory until later

15 June 2020

The mandatory wearing of face masks in public in Germany, for example when shopping or on public transport, clearly contributes to reducing the spread of the coronavirus. Researchers at four universities, among them economist Professor Klaus Wälde from Johannes Gutenberg University Mainz (JGU), came to this conclusion after comparing the rate of growth of COVID-19 case numbers in Jena with that in similar cities. In Jena, mandatory mask wearing had already been introduced on April 6, 2020, much earlier than in any other German regions and cities. After the introduction, there was only a slight increase in the number of registered infections in Jena. With this in view, the researchers wanted to know whether this effect was actually due to the mandatory wearing of face masks or other specific circumstances. "In order to be able to answer this question as objectively as possible, we created a synthetic version of Jena in which mandatory wearing of face masks was introduced at a later period in time. We then compared the results for this with those for the real Jena," explained Wälde.

As described in a recent discussion paper published by the Institute of Labor Economics (IZA), the researchers selected regions and cities that most closely matched Jena in terms of the development of COVID-19 case numbers up to the end of March 2020. In addition, they also took into account the congruity of certain structural criteria, such as population density, average population age, and the availability of doctors and pharmacies. The next step was to calculate the average number of infections in these cities and regions, which would correspond to the number of infection cases that Jena could have had without the introduction of mandatory face masks on April 6, 2020. "According to our calculations, there is a significant disparity between the case numbers in Jena and the comparison group without mandatory face masks," said co-author Professor Timo Mitze of the University of Southern Denmark. Twenty days after the introduction of mandatory face masks in Jena, the total number of COVID-19 cases registered there only increased from 142 to 158, while in the synthetic Jena they increased from 143 to 205. The increase in infections in Jena thus only corresponded to about a quarter of the increase in the comparison group.

In the second stage of the study, the researchers examined the development of COVID-19 case numbers in cities and regions that introduced mandatory face masks on April 22, 2020 with the number of cases in cities and districts that did not introduce mandatory face masks until April 27, 2020 or later. Significant variations also became apparent here. "In summary, it can be said that the introduction of mandatory face masks in the respective regions has contributed to a slowdown in the spread of COVID-19," emphasized Wälde. This conclusion would be consistent with the assessment of epidemiologists and virologists that mouth and nose protection inhibits the flow of air during speech and thus limits the transmission of infectious particles. Wälde also believes it is possible that the masks could have a kind of signaling function in that they remind the population to adhere to the restrictions on social contact. "Our results suggest that compulsory mask-wearing could well be a key component in the future containment of the coronavirus," concluded Wälde.