- A new study has added to the growing proof that face masks slow down the spread of SARS-CoV-2
- The recently published German study looked at Covid-19 cases in 401 regions in the country
- They found that the early introduction of this policy in one city led to a drop in cases by up to 75% after 20 days
Face masks are strongly recommended to reduce the transmission of SARS-CoV-2, the virus that causes Covid-19 disease. In some countries, the wearing of masks has become mandatory.
Previous studies have shown how face masks help to curb the spread of the virus, but researchers of a new German study compared the rise in infections in regions where mask-wearing was compulsory versus regions where it wasn't, and found that 20 days after becoming mandatory, face masks had reduced the number of new infections by around 47%.
“After face masks became mandatory between 1 April and 10 April 2020, the number of new infections fell almost to zero,” the authors wrote. Although this was mainly in the city of Jena, they added that face masks eventually became mandatory in all federal states between 20 April and 29 April 2020.
Their study was published in the peer-reviewed journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).
401 regions studied
For the study, the team used available data of 401 municipal districts in Germany from the Robert Koch Institute to estimate the effect of the mask-wearing policy intervention on the development of registered Covid-19 infections.
They took special precautions to ensure that their analysis of the timing of all public health measures in the regions studied guaranteed that they correctly attributed their findings to face masks, and not to other public health measures.
More than this, they incorporated a standard SIR (susceptible–infected–removed) epidemic model for their analysis and studied the distribution of the lag between infection and reporting date. According to the authors, these precautions allowed them to provide a precise interpretation “to pin down the point in time when the effects of face masks should be visible in the data”.
Focusing on the city of Jena
When studying the population of Jena (nearly 110 000 people), the team found that the early introduction of face masks in that region resulted in a drop in newly registered Covid-19 cases of up to a remarkable 75% after 20 days.
Their findings also show that the daily growth rates in the number of infections when face masks were introduced in Jena was around 2–3% – these are low growth rates compared to the early days of the epidemic in Germany, where daily growth rates were above 50%, they wrote.
“Put simply, if the control region observes 100 new infections over a period of 20 days, the mask region observes only 25 cases.
“This drop is greatest, by more than 90%, for the age group 60 years and above,” they explained, adding that their findings are statistically significant and sufficiently large to support their point that wearing face masks is an effective and cost-efficient measure for fighting Covid-19.
When other regions in the country followed the example of Jena and introduced face masks before the general introduction at the federal state level in mid-April, overall daily growth rates were already lower.
47% drop in Covid growth rate due to mask-wearing
When their findings were summarised in one single measure, they concluded that the daily growth rate of Covid-19 cases fell by around 47% due to mandatory mask-wearing.
These results support earlier evidence on face masks and other public health measures to control the spread of the virus, they said, although noting that scientific knowledge about the topic is still limited.
“While there is a growing consensus from clinical studies that face masks significantly reduce the transmission risk of SARS-CoV-2... non-clinical evidence on the effectiveness of face masks is still largely missing,” they said.
They, therefore, stress the need for further analyses in different countries, as, for example, various types of face masks are used in different countries during the pandemic, and they couldn’t “identify differential effects since mask regulations in German regions do not require a certain type”.
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