Double-masking, or wearing a cloth face covering over a medical procedure mask, increases a person’s protection against exposure to particles of the coronavirus disease 2019 (Covid-19) by more than 90%, according to an analysis released Wednesday by the US Centers for Disease Control and Prevention (CDC).
In addition, when two people in close contact are both double-masking or wearing properly fitted medical procedure masks over their nose and mouth, protection against coronavirus transmission increases by more than 95 percent, the data showed.
The findings highlight the importance of good fit to maximize overall mask performance, the agency researchers said.
“Controlling [Covid-19] transmission is critical not only to reduce the widespread effects of the … pandemic on human health and the economy, but also to slow viral evolution and the emergence of variants,” CDC researchers wrote in the analysis.
“Until vaccine-induced population immunity is achieved, universal masking is a highly effective means to slow the spread of [the virus] … [and] the data in this report underscore the finding that good fit can increase overall mask efficiency,” they wrote.
Experts first proposed the use of double-masking approaches to reduce the amount of virus particles emitted from the nose and mouth of those infected when new strains of Covid-19 emerged and began to spread across the country.
Medical procedure masks, as well as N95 or N99 masks, are the most effective at limiting virus spread via respiratory droplets, according to recent studies.
The addition of a cloth mask not only helps prevent an infected person from spreading the virus, but can also help protect the wearer from exposure to virus-containing droplets, the CDC said.
For this analysis, CDC researchers in January performed multiple experiments to assess two methods designed to improve medical procedure mask performance: double masking, and knotting and tucking the medical procedure mask for closer fit.
In the first experiment, the researchers evaluated how effectively various mask combinations reduced the amount of particles emitted during a cough, by simulating a person coughing and producing airborne droplets from a mouthpiece.
The tested the protection offered by a three-ply medical procedure mask alone, a three-ply cloth cotton mask alone and the three-ply cloth mask covering the three-ply medical procedure mask, or double-masking, they said.
In the second experiment, they evaluated how effectively knotted and tucked medical procedure masks reduced exposure to airborne particles emitted during a period of breathing.
A knotted and tucked mask brings together the corners and ear loops on each side, knotting the ears loops together where they attach to the mask and then tucking in the resulting extra mask material to minimize the side gaps, the researchers said.
A modified simulator was used to simulate a person’s exposure to aerosols produced by another person coughing, they said.
All of the experiments were conducted in a 10-foot-square chamber with 7-foot ceilings, researchers said.
Results from the first experiment demonstrated that the unknotted medical procedure mask alone blocked 42 percent of the particles from a simulated cough and the cloth mask alone blocked 44 percent, the data showed.
However, the combination of the cloth mask covering the medical procedure mask blocked 93 percent of the cough particles, the researchers said.
Adding a cloth mask over a medical procedure mask reduced the cumulative exposure for an unmasked person in close contact by 82 percent, while knotting and tucking the medical procedure mask reduced the exposure for an unmasked person by 63 percent, the data showed.
When two people in close contact are both fitted with a double mask or a knotted and tucked medical procedure mask, cumulative virus particle exposure was reduced by 96 percent, the researchers said.
“Multiple simple ways to improve fit have been demonstrated to be effective,” the researchers wrote.
“Continued innovative efforts to improve the fit of cloth and medical procedure masks to enhance their performance merit attention,” they said.