Masks May Reduce Viral Dose, Some Experts Say

Some independent experts say the paper is a welcome update, given the pervasive idea that wearing a mask is a mostly altruistic act.

“It’s been a real deficiency in the messaging about masking to say that it only protects the other,” said Charles Haas, an environmental engineer and expert in risk assessment at Drexel University. “From the get go, that never made sense scientifically.”

In other settings, too, from hospitals to hair salons, face coverings may have driven down rates of overall infection, perhaps preventing disastrous outbreaks. And countries like Japan, Taiwan and South Korea, where outbreaks quickly sparked a wave of widespread masking, managed to rein in the number of coronavirus-related hospitalizations and deaths early on.

Even in the United States, the slow upward tick in mask-wearing has coincided with what appears to be a more modest death rate, compared to the surge that occurred after the virus first made landfall in North America. These trends have also likely been influenced by increased testing, a downward shift in the average age of people contracting the virus and improvements in coronavirus treatments. Still, masks probably aren’t hurting things, Dr. Gandhi said.

The idea that face coverings can curb disease severity, although not yet proven, “makes complete sense,” said Linsey Marr, an expert in virus transmission at Virginia Tech. “It’s another good argument for wearing masks.”

Dr. Marr and other researchers are still sussing out exactly how much inbound or outbound virus different types of masks block. But based on a wealth of past evidence and recent observations, the amount that’s filtered out is probably high — perhaps 50 percent or more of the larger aerosols being sent in both directions, Dr. Marr said. Certain coverings, like N95 respirators, will do better than others, but even looser-fitting cloths can waylay some viral particles.

Still, some experts are not ready to embrace all ideas about two-way protection.

What’s outlined in Dr. Gandhi’s paper “is still just a theory, and needs more research,” said Nancy Leung, an epidemiologist at the University of Hong Kong. While there’s good evidence that masks reduce the spread of viruses within a population, it’s much harder to nail down how face coverings influence symptoms, Dr. Leung said, in part “because of the difficulty in conducting those studies.”

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