COVID-19 ALERT The New York Times
Maria Van Kerkhove, technical lead on the pandemic at WHO, claimed the global health body had been discussing the possibility of airborne transmission.
The World Health Organization on Tuesday acknowledged for the first time that there was “evidence emerging” that the transmission of the coronavirus is airborne, Reuters reported. The WHO’s admission came after 239 scientists wrote it an open letter claiming that the virus can be transmitted through the air.
Benedetta Allegranzi, WHO’s technical lead for infection prevention and control, said at a media briefing in Geneva, Switzerland, on Tuesday that such evidence was emerging, but it was not definitive. “The possibility of airborne transmission in public settings – especially in very specific conditions, crowded, closed, poorly ventilated settings that have been described, cannot be ruled out,” she said. “However, the evidence needs to be gathered and interpreted, and we continue to support this.”
The claim made by the scientists contradicts previous evidence that suggested that it was transmitted from person to person through droplets from the nose or mouth, which are expelled when a person with the disease coughs, sneezes or speaks. WHO has so far emphasised that the virus can spread through the air only in case of medical procedures that produce aerosols, or droplets smaller than five microns. The global health body has instead promoted frequent hand washing as a means to keep the virus away.
“We have been talking about the possibility of airborne transmission and aerosol transmission as one of the modes of transmission of Covid-19,” Maria Van Kerkhove, technical lead on the pandemic
at the global health body, said at Tuesday’s news briefing. Kerkhove said the WHO will soon publish a scientific paper on the state of knowledge on modes of transmission of the virus.
“A comprehensive package of interventions is required to be able to stop transmission,” Kerkhove said. “This includes not only physical distancing, it includes the use of masks where appropriate in certain settings, specifically where you can’t do physical distancing and especially for healthcare workers.”
Most countries went into complete or partial lockdown when the coronavirus, which originated in China, began to spread earlier this year. If the WHO confirms that the contagion is spread through the air, countries may have to change the public health measures they have adopted to curb the spread of the virus.
Airborne Coronavirus: What You Should Do Now
How to protect yourself from a virus that may be floating indoors? Better ventilation, for starters. And keep wearing those masks.
The coronavirus can stay aloft for hours in tiny droplets in stagnant air, infecting people as they inhale, mounting scientific evidence suggests.
This risk is highest in crowded indoor spaces with poor ventilation, and may help explain super-spreading events reported in meatpacking plants, churches and restaurants.
It’s unclear how often the virus is spread via these tiny droplets, or aerosols, compared with larger droplets that are expelled when a sick person coughs or sneezes, or transmitted through contact with contaminated surfaces, said Linsey Marr, an aerosol expert at Virginia Tech.
Aerosols are released even when a person without symptoms exhales, talks or sings, according to Dr. Marr and more than 200 other experts, who have outlined the evidence in an open letter to the World Health Organization.
W.H.O. to Review Evidence of Airborne Transmission of Coronavirus
What is clear, they said, is that people should consider minimizing time indoors with people outside their families. Schools, nursing homes and businesses should consider adding powerful new air filters and ultraviolet lights that can kill airborne viruses.
Here are answers to a few questions raised by the latest research.
What does it mean for a virus to be airborne?
For a virus to be airborne means that it can be carried through the air in a viable form. For most pathogens, this is a yes-no scenario. H.I.V., too delicate to survive outside the body, is not airborne. Measles is airborne, and dangerously so: It can survive in the air for up to two hours.
How are aerosols different from droplets?
Aerosols are droplets, droplets are aerosols — they do not differ except in size. Scientists sometimes refer to droplets less than five microns in diameter as aerosols. (By comparison, a red blood cell is about five microns in diameter; a human hair is about 50 microns wide.)
From the start of the pandemic, the W.H.O. and other public health organizations have focused on the virus’s ability to spread through large droplets that are expelled when a symptomatic person coughs or sneezes.
These droplets are heavy, relatively speaking, and fall quickly to the floor or onto a surface that others might touch. This is why public health agencies have recommended maintaining a distance of at least six feet from others, and frequent hand washing.
But some experts have said for months that infected people also are releasing aerosols when they cough and sneeze. More important, they expel aerosols even when they breathe, talk or sing, especially with some exertion.
Scientists know now that people can spread the virus even in the absence of symptoms — without coughing or sneezing — and aerosols might explain that phenomenon.
Because aerosols are smaller, they contain much less virus than droplets do. But because they are lighter, they can linger in the air for hours, especially in the absence of fresh air. In a crowded indoor space, a single infected person can release enough aerosolized virus over time to infect many people, perhaps seeding a superspreader event.
For droplets to be responsible for that kind of spread, a single person would have to be within a few feet of all the other people, or to have contaminated an object that everyone else touched. All that seems unlikely to many experts: “I have to do too many mental gymnastics to explain those other routes of transmission compared to aerosol transmission, which is much simpler,” Dr. Marr said.
Can I stop worrying about physical distancing and washing my hands?
Physical distancing is still very important. The closer you are to an infected person, the more aerosols and droplets you may be exposed to. Washing your hands often is still a good idea.
What’s new is that those two things may not be enough. “We should be placing as much emphasis on masks and ventilation as we do with hand washing,” Dr. Marr said. “As far as we can tell, this is equally important, if not more important.”
Should I begin wearing a hospital-grade mask indoors? And how long is too long to stay indoors?
Health care workers may all need to wear N95 masks, which filter out most aerosols. At the moment, they are advised to do so only when engaged in certain medical procedures that are thought to produce aerosols.
For the rest of us, cloth face masks will still greatly reduce risk, as long as most people wear them. At home, when you’re with your own family or with roommates you know to be careful, masks are still not necessary. But it is a good idea to wear them in other indoor spaces, experts said.
As for how long is safe, that is frustratingly tough to answer. A lot depends on whether the room is too crowded to allow for a safe distance from others and whether there is fresh air circulating through the room.
What does airborne transmission mean for reopening schools and colleges?
This is a matter of intense debate. Many schools are poorly ventilated and are too poorly funded to invest in new filtration systems. “There is a huge vulnerability to infection transmission via aerosols in schools,” said Don Milton, an aerosol expert at the University of Marylan.
Most children younger than 12 seem to have only mild symptoms, if any, so elementary schools may get by. “So far, we don’t have evidence that elementary schools will be a problem, but the upper grades, I think, would be more likely to be a problem,” Dr. Milton said.
College dorms and classrooms are also cause for concern.
Dr. Milton said the government should think of long-term solutions for these problems. Having public schools closed “clogs up the whole economy, and it’s a major vulnerability,” he said.
“Until we understand how this is part of our national defense, and fund it appropriately, we’re going to remain extremely vulnerable to these kinds of biological threats.”
What are some things I can do to minimize the risks?
Do as much as you can outdoors. Despite the many photos of people at beaches, even a somewhat crowded beach, especially on a breezy day, is likely to be safer than a pub or an indoor restaurant with recycled air.
But even outdoors, wear a mask if you are likely to be close to others for an extended period.
When indoors, one simple thing people can do is to “open their windows and doors whenever possible,” Dr. Marr said. You can also upgrade the filters in your home air-conditioning systems, or adjust the settings to use more outdoor air rather than recirculated air.
Public buildings and businesses may want to invest in air purifiers and ultraviolet lights that can kill the virus. Despite their reputation, elevators may not be a big risk, Dr. Milton said, compared with public bathrooms or offices with stagnant air where you may spend a long time.
If none of those things are possible, try to minimize the time you spend in an indoor space, especially without a mask. The longer you spend inside, the greater the dose of virus you might inhale.
