If Aerosols Transmit Covid-19, It Is Even More Prudent to Wear Masks

(p. A1) The coronavirus is finding new victims worldwide, in bars and restaurants, offices, markets and casinos, giving rise to frightening clusters of infection that increasingly confirm what many scientists have been saying for months: The virus lingers in the air indoors, infecting those nearby.

If airborne transmission is a significant factor in the pandemic, especially in crowded spaces with poor ventilation, the consequences for containment will be significant. Masks may be needed indoors, even in socially-distant settings. Health care workers may need N95 masks that filter out even the smallest respiratory droplets as they care for coronavirus patients.

Ventilation systems in schools, nursing homes, residences and businesses may need to minimize recirculating air and add powerful new filters. Ultraviolet lights may be needed to kill viral particles floating in tiny droplets indoors.

The World Health Organization has long held that the coronavirus is spread primarily by large respiratory droplets that, once expelled by infected people in coughs and sneezes, fall quickly to the floor.

But in an open letter to the W.H.O., 239 scientists in 32 countries have outlined the evidence showing that smaller particles can infect people, and are calling for the agency to revise its recommendations. The researchers plan to publish their letter in a (p. A5) scientific journal this week.

. . .

Dr. Benedetta Allegranzi, the W.H.O.’s technical lead on infection control, said the evidence for the virus spreading by air was unconvincing.

. . .

But interviews with nearly 20 scientists — including a dozen W.H.O. consultants and several members of the committee that crafted the guidance — and internal emails paint a picture of an organization that, despite good intentions, is out of step with science.

Whether carried aloft by large droplets that zoom through the air after a sneeze, or by much smaller exhaled droplets that may glide the length of a room, these experts said, the coronavirus is borne through air and can infect people when inhaled.

. . .

But the infection prevention and control committee in particular, experts said, is bound by a rigid and overly medicalized view of scientific evidence, is slow and risk-averse in updating its guidance and allows a few conservative voices to shout down dissent.

“They’ll die defending their view,” said one longstanding W.H.O. consultant, who did not wish to be identified because of her continuing work for the organization. Even its staunchest supporters said the committee should diversify its expertise and relax its criteria for proof, especially in a fast-moving outbreak.

“I do get frustrated about the issues of airflow and sizing of particles, absolutely,” said Mary-Louise McLaws, a committee member and epidemiologist at the University of New South Wales in Sydney.

“If we started revisiting airflow, we would have to be prepared to change a lot of what we do,” she said. “I think it’s a good idea, a very good idea, but it will cause an enormous shudder through the infection control society.”

. . .

“There is no incontrovertible proof that SARS-CoV-2 travels or is transmitted significantly by aerosols, but there is absolutely no evidence that it’s not,” said Dr. Trish Greenhalgh, a primary care doctor at the University of Oxford in Britain.

“So at the moment we have to make a decision in the face of uncertainty, and my goodness, it’s going to be a disastrous decision if we get it wrong,” she said. “So why not just mask up for a few weeks, just in case?”

For the full story, see:

Mandavilli, Apoorva. “Scientists Insist Airborne Spread Is a Threat as the W.H.O. Wavers.” The New York Times (Monday, July 6, 2020, 2020): A1 & A5.

(Note: ellipses added.)

(Note: the online version of the story was updated July 7, 2020, and has the title “239 Experts With One Big Claim: The Coronavirus Is Airborne.” Where there is a minor difference in wording between the print and online versions, the passages above follow the print version.)

The open letter with two co-authors, but endorsed by 239 scientists, is:

Morawska, Lidia, and Donald K Milton. “It Is Time to Address Airborne Transmission of Covid-19.” Clinical Infectious Diseases (published online in advance of print July 6, 2020).

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