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 WHO, 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 scientific journal.

Proper ventilation and N95 masks are of concern only in those circumstances, according to the WHO. Instead, its infection control guidance, before and during this pandemic, has heavily promoted the importance of handwashing as a primary prevention strategy, even though there is limited evidence for transmission of the virus from surfaces. (The Centers for Disease Control and Prevention now says surfaces are likely to play only a minor role.)

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

“Especially in the last couple of months, we have been stating several times that we consider airborne transmission as possible but certainly not supported by solid or even clear evidence,” she said. “There is a strong debate on this.”

But interviews with nearly 20 scientists — including a dozen WHO 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.

Most of these experts sympathized with the WHO’s growing portfolio and shrinking budget, and noted the tricky political relationships it has to manage, especially with the United States and China. They praised WHO staff for holding daily briefings and tirelessly answering questions about the pandemic.

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 long-standing WHO 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.

In interviews, other scientists criticized this view as paternalistic. “‘We’re not going to say what we really think, because we think you can’t deal with it?’ I don’t think that’s right,” said Don Milton, an aerosol expert at the University of Maryland.

Even cloth masks, if worn by everyone, can significantly reduce transmission, and the WHO should say so clearly, he added.

Several experts criticized the WHO’s messaging throughout the pandemic, saying the staff seems to prize scientific perspective over clarity.

In a less public instance, the WHO said there was “no evidence to suggest” that people with HIV were at increased risk from the coronavirus. After Joseph Amon, a longtime WHO associate and director of global health at Drexel University in Philadelphia, pointed out that the phrasing was misleading, the WHO changed it to say the level of risk was “unknown.”

 

 

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