CDC changes guidance, retracts
Health officials say Friday’s post regarding small aerosol transmission was a mistake
NEW YORK » The top U.S. public health agency has stirred confusion by posting — and then taking down — an apparent change in its position on how easily the coronavirus can spread from person to person on small droplets in the air.
Officials at the Centers for Disease Control and Prevention say the virus spreads primarily through small airborne droplets, like those that fly through the air when someone coughs or sneezes. Most CDC guidance about social distancing is built around that idea, saying that 6 feet is a safe buffer between people who are not wearing masks.
In interviews, CDC officials have also acknowledged growing evidence that the virus can in some cases also spread via even smaller, aerosolized particles or droplets that spread over a wider area. That’s one of the reasons public health experts stress wearing a mask, which can stop or reduce contact with both larger droplets and aerosolized particles.
The CDC has maintained that the spread is mainly through the larger droplets. And for months the website said little about aerosolized particles. So the agency’s position appeared to have changed when the CDC on Friday quietly posted an update that discussed aerosolized particles in more detail. The post added singing and breathing to the ways the virus can go airborne, and said the coronavirus can remain suspended in the air and drift more than 6 feet. It also emphasized the importance of ventilation indoors.
Federal health officials on Monday said the posting Friday was a mistake, put out before full editing and clearance was completed. They said the CDC is planning to clarify the agency’s thinking, but it did not immediately release a statement or revision.
“A draft version of proposed changes to these recommendations was posted in error to the agency’s official website,” the agency said, and that once the final version is complete, “the update language will be posted.”
More than 200 experts in aerosol transmission appealed to the World Health Organization in July to review the evidence on aerosol transmission of the corona
virus. The WHO acknowledged that this route appears to contribute significantly to the spread of the pandemic, but health experts disagree as to its importance relative to the heavier respiratory droplets that are sneezed or coughed by infected patients.
“In the scientific community, it’s become very clear that aerosols are very important,” said Linsey Marr, an expert in airborne viruses at Virginia Tech. “I hope that it comes back in some form that acknowledges the importance of aerosols.”
The CDC has come under attack for past revisions of guidance during the pandemic, some of which were driven by political considerations by the Trump administration.
In another change of guidance on its website, the CDC said in August that people who were in close contact with an infected person but had no symptoms didn’t need to get tested. But last week, after The New York Times reported that the guidance was dictated by political appointees in the administration rather than by scientists, the agency reversed its position and said all close contacts of infected people should be tested regardless of symptoms.
Some said that whatever drove the most recent confusion, the episode may further chip away public confidence in the CDC.
“The consistent inconsistency in this administration’s guidance on COVID-19 has severely compromised the nation’s trust in our public health agencies,” said Dr. Howard Koh, a Harvard University public health professor who was a high-ranked official in the U.S. Department of Health and Human Services during the Obama administration.
“To rectify the latest challenge, the CDC must acknowledge that growing scientific evidence indicates the importance of airborne transmission through aerosols, making mask wearing even more critical as we head into the difficult fall and winter season,” Koh said in a statement.
Dr. Mike Ryan, the executive director of World Health Organization Health Emergencies Program, said that while the United States waits on final advice from the CDC, the world cannot wait to find ways to stop the spread of the disease.
“Based on the evidence, [WHO] believes there is a wide range of transmission modes,” Ryan said. “We believe the disease is predominately or primarily spread through droplets spread and through larger droplet nuclei. But we have always said that smaller droplet nuclei can spread this disease — and that is very context driven.”
Ryan explained that people who are in a small indoor area with poor ventilation can become infected through aerosol-based transmission. It’s all about knowing risk and “managing the frequency, intensity and duration” of time spent around others in crowded spaces, he said.