In a move praised by aerosol experts Monday, the Centers for Disease Control and Prevention posted an update to its COVID-19 page seeming to acknowledge that the virus can spread through aerosols. The particles, which are much smaller than large respiratory droplets, are capable of lingering in the air longer, as well as traveling further than 6 feet.
Great to see comparison....clear guidance, finally. pic.twitter.com/UHT84QZHQk
— Kimberly Prather, Ph.D. (@kprather88) September 20, 2020
“COVID-19 most commonly spreads through respiratory droplets or small particles, such as those in aerosols, produced when an infected person coughs, sneezes, sings, talks or breathes,” the CDC wrote in an update published to its website on Friday. Not long after the update garnered praise from scientists on Twitter, the new guidance was removed on Monday and replaced by a note saying that it was posted erroneously.
“A draft version of proposed changes to these recommendations was posted in error to the agency’s official website,” the page now reads. “CDC is currently updating its recommendations regarding airborne transmission of SARS-CoV-2 (the virus that causes COVID-19). Once this process has been completed, the update language will be posted.”
No timeline on when the guidance will return has been shared, and neither the CDC nor the National Institutes of Health responded to Yahoo Life’s requests for comment. But the endorsement of the aerosol transmission theory, followed by a quick reversal, has further inflamed an existing debate on the issue in the science world, with aerosol experts insisting airborne transmission is fueling the pandemic and infectious disease experts insisting that the epidemiological data suggests otherwise.
Until the post is updated — and as the debate rages on — here’s what you need to know.
Aerosol experts and epidemiologists disagree over whether aerosols are at play
Kimberly Prather director for the National Science Foundation’s Center for Aerosol Impacts on Chemistry of the Environment (CAICE) at the University of California, San Diego, tells Yahoo Life that “scientists have known that the virus could spread through aerosols” since February, adding that “the evidence has only gotten stronger.” Multiple studies have discussed how SARS-CoV-2 — the virus that causes COVID-19 — can be found in aerosols, including one in the Lancet from May and another from the NEJM in April.
But many epidemiologists disagree that the mere presence of the virus in aerosols means it’s a major route of transmission. Dr. Amesh Adalja, an infectious disease physician and senior scholar at the Johns Hopkins Center for Health Security, suggests that if aerosol spread were a major factor, the pandemic would be playing out differently. “There’s not a question about whether ... there may be some aerosolization or whether you can isolate the virus from the air,” Adalja tells Yahoo Life. “But the question then becomes, does that finding of the virus in the air translate to an infection risk and are people getting infected in that manner?”
From what Adalja — who’s long been on the frontlines of the COVID-19 crisis — has seen, the answer is no. “When you look at the epidemiology, for example, looking at household infection rates, they’re only about 20 percent in some studies, meaning only 20 percent of the people in the household get infected,” he says. “You had to expect it to be much higher.” Measles, he says, which is mainly spread through aerosols, has a 100 percent household infection rate. “We don’t even test the other people. If they’re not vaccinated, we just assume that they’ve got measles.”
Both seem to agree that aerosols may be at play during large events
While Adalja doesn’t believe that aerosols are the main route of transmission, he says that it’s plausible that there may be some situations in which airborne transmission is occurring. “I can make distinctions that maybe in a church choir practice where people are singing that becomes important. Or when you’re doing aerosol-generating procedures like intubation,” he says. “But when I'm taking care of a COVID patient, I’m not necessarily wearing airborne precautions with an N95 mask unless there's an aerosol-generating procedure going on.”
Dr. Saskia Popescu, an infection prevention epidemiologist at George Mason University, agrees that the issue is thorny. “Droplet and aerosol are the major ways of transmission and often, hard to distinguish in clusters,” Popescu tells Yahoo Life. “In many of the outbreaks/super-spreader events occurring we’ve seen, this points to close contact and the role of indoor transmission (ventilation, density, space, et cetera.).”
Aerosols and large respiratory droplets spread the virus in different ways
In a tweet thread responding to the news Monday morning, Dr. Jose-Luis Jimenez, a professor of chemistry at the University of Colorado and one of the leading experts on aerosols in the U.S., called the development “HUGE news.” Jimenez, who could not be reached for comment, linked to a previously crafted document he wrote explaining what aerosol spread entails.
“When we talk, shout, sing, cough, sneeze or simply breathe, we exhale small particles (‘aerosols’) that are made of saliva or respiratory fluid (the liquid that wets the inside of your trachea, lungs etc.),” Jimenez writes. “These aerosols are the ‘carriers’ of SARS-CoV-2 viruses, and can infect when they are inhaled.”
That’s one of the major distinctions that Jimenez shares — that while large respiratory droplets can only travel approximately six feet, and must make contact with another individual’s eyes, nose or mouth, aerosols can spread the virus simply by being inhaled. This means they can infect many more individuals — including those who are over 6 feet away.
On top of that, according to Jimenez is the fact that they have a longer “lifetime” in the air than respiratory droplets, meaning they stay suspended longer. “Overall it seems that the lifetime may be about 1-2 hours at typical room temperature (70ºF),” Jimenez writes. Other experts have suggested that it may even be three hours.
6 feet is not “some magical barrier”
Prather, who praised the CDC’s initial acknowledgment, outlines the implications of aerosol transmission and shares what Americans can do to stay safe. “Ventilation and filtration will ‘clean the air’ — aerosols are readily filtered out so this would reduce the spread,” she says. Prather adds that indoor events, especially where individuals aren’t wearing masks, are the “riskiest” — which is part of the reason she considers the aerosol guidance to be vital to reopening the U.S.
“Otherwise, schools and businesses will continue just to wipe surfaces — and this is not stopping one from inhaling the infectious virus in aerosols,” says Prather. “Also, if you are in the room with someone, distance is important AND you should also wear a mask because aerosols travel much further than six feet. Their concentrations can build up indoors. Outdoors is much safer than indoors due to dilution.”
Popescu agrees that the aerosol debate highlights the need for distance, both indoors and outdoors. “The biggest takeaway is that the 6-feet rule is not some magical barrier that means germs can’t pass it,” says Popescu. “If you’re indoors and at 6 feet or more, you should still wear a mask when around others. Droplets are something we see occurring within 6 feet, while aerosols are smaller and can linger in the air longer and go farther than 6 feet.”
Either way, Popescu says that the CDC removing the guidance may allow for more clarity — both for Americans and experts. “Ultimately, I’m hoping that pulling back the document will allow for the CDC to do a bit more [science communication] about what aerosols are and what they mean for the general public.”
For the latest coronavirus news and updates, follow along at https://news.yahoo.com/coronavirus. According to experts, people over 60 and those who are immunocompromised continue to be the most at risk. If you have questions, please reference the CDC’s and WHO’s resource guides.
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