Story at a glance

  • A new study suggests early adoption of face masks in public can reduce coronavirus cases by 40 percent.
  • The study observed a German town that adopted masks before other comparable locations.

A German study documenting the effect of face masks on the spread of coronavirus infections in a single town suggests that using face coverings can reduce transmission by approximately 40 percent.

The study, released this month and authored by the IZA Institute of Labor Economics, analyzed the city of Jena in the province of Thuringia, Germany. Face masks were mandated by law in all German provinces between April 20 and April 29, but Jena had adopted the habitual use of face masks notably earlier, around April 6. The study says that after face masks were introduced, cases in the town fell to almost zero. 

Researchers used a synthetic control unit formed from weighted averages of control regions similar to Jena in terms of demographics, known COVID-19 infection levels, and local health care apparatuses. The synthetic control unit represented a comparable town that adopted compulsory face masks later than April 6, the time Jena’s residents began wearing them in public. 

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The study identified a widening gap of the total number of coronavirus cases between Jena and the synthetic control unit. Among their findings, researchers reported that within the first 20 days of wearing face masks in Jena, by April 26, corresponded to a drop in coronavirus cases by almost 25 percent. This is compared with the control group, whose case number continues to grow. 

Earlier, within the first 10 days, researchers saw a decline in new cases by 13 percent. 

This resulted in a reduction in the daily growth rate by approximately 40 percent as a result of earlier introduction of face masks in Jena relative to the synthetic town. Described in percentage points, this reduction translates to a 1.32 percentage point decrease in the average daily growth rate of coronavirus infections.

When applying the same treatment of earlier face mask adoption to a sub-sample of 105 larger German cities, data continues to suggest that there is a “significant face mask-effect in the reduction of Covid-19 infections,” noting a decline in cases from introducing masks from April 6 to April 26.

While these results were verified with a placebo-in-time test as well as cross validation, the authors stress the need for more detailed and comprehensive studies, primarily outside of Germany to further control for any confounding variables or biases.

As states in the U.S. begin to reopen, and the usage of masks is mandated in some locations throughout the country, this data could provide further guidance for public health experts weighing the decision to mandate mask usage in public. 


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Published on Jun 12, 2020