People who report they always wear a mask or respirator in indoor public settings were less likely to test positive for COVID-19 than people who did not, according to the CDC's Feb. 4 Morbidity and Mortality Weekly Report.
Researchers randomly selected California residents who received a COVID-19 test result from Feb. 18 to Dec. 1, 2021. They assessed mask or respirator use among 652 participants who tested positive and 1,176 participants who tested negative. All participants had self-reported being in indoor public settings during the two weeks before testing and had no knowledge of exposure to someone with a confirmed or suspected infection.
Those who reported always using a face mask or respirator indoors compared to those who said they never masked indoors were less likely to test positive for COVID-19, with an adjusted odds ratio of 0.44 percent. The protection increased as the quality of mask increased, based on an analysis of 534 participants who reported their mask type. Those who reported consistently wearing a cloth mask had 56 percent lower odds of testing positive. The figure rose to 66 percent for surgical masks and 83 percent for N95 and KN95 respirators.
Laboratory studies have demonstrated masks' effectiveness, though few studies have focused on their real world efficacy, the report said.
"These findings reinforce that in addition to being up to date with recommended COVID-19 vaccinations, consistently wearing a face mask or respirator in indoor public settings reduces the risk of acquiring SARS-CoV-2 infection," researchers said. "Using a respirator offers the highest level of personal protection against acquiring infection, although it is most important to wear a mask or respirator that is comfortable and can be used consistently."