People around the world don homemade masks in an effort to curb the transmission of the coronavirus. But there is not enough data to know for sure whether such cloth masks will prevent an infected person from transmitting the virus to another person, experts say.
Faced with evidence that the coronavirus can be spread by speaking and breathing, as well as coughing or sneezing, the Centers for Disease Control and Prevention recommended that people cover their faces with a cloth or cloth when going out in public.
The cloth can reduce some large respiratory droplets from coughing or sneezing, but it is unclear whether it will also catch smaller droplets called aerosols that are released simply by breathing or speaking.
Cloth masks, as well as surgical masks, are designed to protect others from the virus transmitted by the mask wearer, not the other way around. People infected with the virus that causes COVID-19 can transmit it to others before they begin to show symptoms. When masks are used as a general habit, their goal is to prevent people who don't know they are sick from inadvertently passing the virus to others. Wearing a mask is not intended to be a replacement for social distancing, hand washing, and other endeavors.
But there are few studies evaluating the effectiveness of cloth masks in preventing the spread of respiratory diseases, researchers from the U.S. National Academies of Sciences, Engineering and Medicine wrote in an April 8 letter to the Office of Policy. of Science and Technology of the White House.
Those that do exist suggest that cloth masks can capture large respiratory droplets, such as those from coughing or sneezing. Those made of different types of cloth have a broad capacity to filter virus-sized particles, with a trade-off between filtration and the ability to breathe.
In one study, a mask using 16 layers of bandana fabric was able to filter out 63 percent of 300-nanometer-sized particles. (The coronavirus is between 50 and 200 nanometers in diameter.) But that mask was harder to breathe compared to the thick, tight-fitting N95 respirators often used in hospitals, which can block tiny particles. Wearing a fabric mask with so many layers would be uncomfortable and could "make some swoon," the researchers wrote in the letter.
Surgical masks are somewhat less mysterious. Those masks can help reduce the transmission of flu and seasonal coronaviruses that cause common colds in people with symptoms, researchers reported April 3 in Nature Medicine. The researchers quantified the amount of virus exhaled by the participants with and without a surgical mask over 30 minutes.
Those masks significantly reduced the amount of detectable influenza virus in respiratory droplet particles, as well as the amount of seasonal coronavirus in aerosols.
Regardless of how well they work, the success of surgical cloth or masks in protecting others depends on whether people use the equipment correctly, including keeping it in place, and making sure it doesn't get too wet. Moisture, such as breath, can trap the virus in a mask and make it a major source of contamination when the user removes it.
Though evidence for cloth masks is scant, health officials should still encourage people to wear face masks, other researchers write in an April 9 analysis in the BMJ. Limited protection could still save lives. "As with parachutes for jumping out of planes, it's time to act" without waiting for evidence, say the authors.