What is the problem and what is known about it so far?
Masks are used to prevent the spread of COVID-19 and have become routine in health care settings. It is uncertain whether medical masks provide less protection than N95 respirator masks to health care workers.
Why did the researchers do this particular study?
The researchers wanted to see if there were important differences by mask type in preventing COVID-19 in health care workers.
Who was studied?
A total of 1009 health care workers who provided direct care to patients with suspected or confirmed COVID-19 in 29 inpatient settings in Canada, Israel, Pakistan, and Egypt. To be eligible for the study, participants could not have received a highly effective COVID-19 vaccine or had a known COVID-19 infection.
How was the study done?
The researchers randomly assigned each participant to wear either a medical mask or an N95 respirator mask while at work for 10 weeks. All sites required staff to wear masks at all times at work. Participants then had nasal swabs for polymerase chain reaction COVID-19 tests if they developed symptoms. The researchers initially planned to enroll all participants in Canada but added the other countries when COVID-19 vaccination became available in Canada, making health care workers in Canada ineligible for the study.
What did the researchers find?
Overall, confirmed COVID-19 occurred in 10.46% of the medical mask group versus 9.27% in the N95 respirator group. However, the results varied by country: 6.11% versus 2.22% in Canada, 35.29% versus 23.53% in Israel, 3.26% versus 2.13% in Pakistan, and 13.62% versus 14.56% in Egypt.
What were the limitations of the study?
There were differences between the countries related to which COVID-19 variant was circulating and how many participants had an undiagnosed previous infection when the data were being collected in that country. Although vaccination with a highly effective vaccine excluded participants, many participants in Pakistan and Egypt had been vaccinated but with less effective vaccines. In addition, the study was designed to examine a fairly large difference in infection risk and was unable to detect smaller differences.
What are the implications of the study?
When the researchers combined results from all the countries, the findings suggested that infection risk was not double or more with medical masks compared with N95 respirators. The findings by country varied, and this may have been due to differences in vaccine use, the number of people with previous infection, and the type of variant circulating.
Footnotes
This article was published at Annals.org on 29 November 2022.