The World Health Organization on Thursday formally acknowledged that droplets carrying the coronavirus may be airborne indoors and that people who spend long periods in crowded settings with inadequate ventilation may be at risk of becoming infected, a reversal that many scientists said was long overdue. And it also acknowledged unequivocally that the virus can be transmitted by people who do not have symptoms.
Apoorva Mandavilli reports on the admission, which came after a push by more than 200 experts prompted the agency to update its description of how the virus is spread. The agency now says transmission of the virus by aerosols, or tiny droplets, may have been responsible for “outbreaks of Covid-19 reported in some closed settings, such as restaurants, nightclubs, places of worship or places of work where people may be shouting, talking, or singing.”
The W.H.O. still largely emphasizes spread of the virus by larger droplets that are coughed or inhaled, or from contact with a contaminated surface, also known as “fomite transmission.” And in a longer document on the scientific evidence, the agency still maintains that “detailed investigations of these clusters suggest that droplet and fomite transmission could also explain human-to-human transmission within these clusters.”
In addition to avoiding close contact with infected people and washing hands, the W.H.O. has said people should “avoid crowded places, close-contact settings, and confined and enclosed spaces with poor ventilation.” Homes and offices should ensure good ventilation, the agency said.
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“It is refreshing to see that W.H.O. is now acknowledging that airborne transmission may occur, although it is clear that the evidence must clear a higher bar for this route compared to others,” said Linsey Marr, an aerosol expert at Virginia Tech.
Still, the updated guidance is not as extensive as many experts hoped to see.
The W.H.O. had previously maintained that airborne spread is only a concern when health care workers were engaged in certain medical procedures that produce aerosols. But mounting evidence has suggested that in crowded indoor spaces, the virus can stay aloft in the air for hours and infect others when inhaled, and may even seed super-spreader events.