COVID-19 can possibly spread through airborne aerosols, definitely via people without symptoms, WHO says

The World Health Organization updated its findings Thursday on how COVID-19 is transmitted, and there are two important changes. First, the WHO acknowledged growing evidence the new coronavirus may spread through aerosols, tiny droplets of saliva that linger in the air for hours, especially in enclosed and poorly ventilated spaces. The second change involved the risk of transmission by people who don't have symptoms. Both issues have broad implications for how to contain the disease.

The WHO maintains that the main route of transmission involves infected people projecting saliva droplets into the eyes, mouth, or nose of people in close proximity, via coughing, sneezing, talking, or singing. The agency also said spread through infected surfaces, or formite transmission, is "likely" though not yet proven. Urine and feces have been shown to contain viable amount of the new coronavirus, too.

The virus can be spread by people who don't have COVID-19 symptoms, the WHO said, but there is an "important" distinction between people who never develop symptoms (asymptomatic) and those who have yet to develop symptoms (presymptomatic), and "the extent of truly asymptomatic infection in the community remains unknown." As a practical matter, Michael Barbaro noted on Thursday's The Daily podcast, the WHO is "making distinctions that don't mean all that much to people who are trying to decide whether to go to work, whether to go to a restaurant, whether to see friends."

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The WHO has long dismissed aerosols as a means of transmission except during certain medical procedures, but it now says airborne spread "cannot be ruled out." There's evidence aerosols 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 WHO said, though larger droplets or contaminated surfaces might also have caused those outbreaks.

"Outdoors, any virus in small or large droplets may be diluted too quickly in the air to pose a risk," The New York Times reports. "But even a small possibility of airborne spread indoors has enormous implications for how people should protect themselves." The new brief mostly shows the WHO's experts interpret the data on aerosols differently, Oxford University's Dr. Trish Greenhalgh tells the Times. "The push-pull of that committee is palpable," she said. "As everyone knows, if you ask a committee to design a horse, you get a camel."