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N95, KN95 masks provide best protection against covid, CDC study shows

N95 masks are now the preferred face covering to protect yourself and others from the coronavirus. Here is what you need to know. (Video: Daron Taylor, John Farrell/The Washington Post)

Wearing any kind of mask indoors is associated with significantly better protection from the coronavirus, with high-quality N95 and KN95 masks providing the best chance of avoiding infection, the Centers for Disease Control and Prevention reported Friday.

In indoor public settings, surgical masks reduce the chances of testing positive by 66 percent, the CDC estimated. Top-of-the-line N95 and KN95 masks, the tightfitting face coverings often worn by health-care workers, cut the odds of infection by 83 percent, the health agency said.

Wearing a cloth mask appeared to lower the odds of testing positive by 56 percent, but the findings were not statistically significant.

“These data from real-world settings reinforce the importance of consistently wearing face masks or respirators to reduce the risk of acquisition of SARS-CoV-2 infection among the general public in indoor community settings,” the CDC said in its Morbidity and Mortality Weekly Report.

Your N95 mask questions, answered

Mask-wearing has been a flash point for conflict from the earliest days of the coronavirus pandemic, when health officials told the public not to buy masks, which they said at the time should be conserved for medical professionals. The government soon reversed course on masking against the airborne virus and urged everyone to wear face coverings.

Arguments over whether to mandate mask-wearing, who has the authority to order it and under what circumstances have endured to this day.

“There are still people who say masks don’t work,” said Linsey C. Marr, an expert on airborne virus transmission at Virginia Tech who was not involved in the new research. She said the CDC report bolsters the well-known value of mask-wearing by providing additional real-world data.

Similarly, Jose-Luis Jimenez, a professor of chemistry at the University of Colorado who did not take part in the study, said in an email that it “adds more evidence to what we already know: this is mainly an airborne virus, and for that reason we have an indoor pandemic. Wearing masks indoors reduces transmission, with the protective effect increasing for better mask quality and fit.”

The research was conducted by the California Department of Public Health between Feb. 18 and Dec. 1, 2021 — before the omicron variant wave hit the United States. Researchers surveyed 652 people who had recently tested positive for the virus and matched them with 1,176 who had tested negative. All were asked whether they had been in stores, churches, schools, restaurants and other indoor public settings in the 14 days before their test, whether they had worn a mask and how often. They also were matched by their vaccination status, among other characteristics.

In the last three months of the survey, 534 of the participants were asked what kind of mask they wore.

The researchers acknowledged that relying on participants’ recall of their behavior in multiple public indoor settings may have limited the reliability of the results, though they took steps to minimize the impact. They also did not account for other preventive steps participants may have taken, such as physical distancing.

Nevertheless, the advantages of mask-wearing were found to be substantial. They reinforced laboratory and other real-world testing that shows masks are an effective barrier to the coronavirus.

“What this shows is if you pay attention and wear a good mask and wear it all the time, you have a significantly lower risk of testing positive for covid-19,” Marr said.