The agency also explained more directly that people without symptoms may spread the virus.


A restaurant in São Paulo, Brazil, on July 6. The coronavirus may linger in the air indoors and infect people, the W.H.O. acknowledged.Credit...Sebastiao Moreira/EPA, via Shutterstock, By Apoorva Mandavilli - July 9, 2020


Article Link: https://www.nytimes.com/2020/07/09/health/virus-aerosols-who.html?referringSource=articleShare


The coronavirus may linger in the air in crowded indoor spaces, spreading from one person to the next, the World Health Organization acknowledged on Thursday.

The W.H.O. had described this form of transmission as doubtful and a problem mostly in medical procedures. But growing scientific and anecdotal evidence suggest this route may be important in spreading the virus, and this week more than 200 scientists urged the agency to revisit the research and revise its position.

In an updated scientific brief, the agency also asserted more directly than it had in the past that the virus may be spread by people who do not have symptoms: “Infected people can transmit the virus both when they have symptoms and when they don’t have symptoms,” the agency said.

The W.H.O. previously said asymptomatic transmission, while it may occur, was probably “very rare.”

Some experts said both revisions were long overdue, and not as extensive as they had hoped.


The coronavirus may linger in the air in crowded indoor spaces, spreading from one person to the next, the World Health Organization acknowledged on Thursday.

The W.H.O. had described this form of transmission as doubtful and a problem mostly in medical procedures. But growing scientific and anecdotal evidence suggest this route may be important in spreading the virus, and this week more than 200 scientists urged the agency to revisit the research and revise its position.

In an updated scientific brief, the agency also asserted more directly than it had in the past that the virus may be spread by people who do not have symptoms: “Infected people can transmit the virus both when they have symptoms and when they don’t have symptoms,” the agency said.

The W.H.O. previously said asymptomatic transmission, while it may occur, was probably “very rare.”

Some experts said both revisions were long overdue, and not as extensive as they had hoped.


These recommendations are “what is needed to help slow transmission in communities,” Dr. Marr said.

There is debate about the relative contribution of airborne spread, compared with transmission by droplets and surfaces. The new brief still skirts that question.

“I interpret this as saying, ‘While it is reasonable to think it can happen, there’s not consistent evidence that it is happening often,’” Bill Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health, said in an email.

After The Times reported that an international group of 239 experts planned to call on the W.H.O. to review the research, Dr. Benedetta Allegranzi, head of the agency’s infection prevention and control committee, said on Tuesday that the possibility of airborne spread in “crowded, closed, poorly ventilated settings” could not be ruled out.

Outdoors, any virus in small or large droplets may be diluted too quickly in the air to pose a risk. But even a small possibility of airborne spread indoors has enormous implications for how people should protect themselves.

People may need to minimize time indoors with others from outside the household, in addition to maintaining a safe distance and wearing cloth face coverings. Businesses, schools and nursing homes may need to invest in new ventilation systems or ultraviolet lights that destroy the virus.

Some experts have criticized the W.H.O. for being slow to acknowledge the possibility of airborne spread while emphasizing hand washing as the primary preventive strategy. Even in the new brief, it’s clear that members of the committee interpreted the evidence differently, said Dr. Trish Greenhalgh, a professor of primary health care at the University of Oxford.

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