The news: The US Centers for Disease Control and Prevention has updated its guidelines to acknowledge that the coronavirus can be spread by tiny particles that linger in the air. The agency said it made the decision because of the mounting evidence that people with covid-19 can infect people even if they are more than six feet away, or shortly after the infected person left the area. These cases all occurred in poorly ventilated and enclosed spaces, and often involved activities that cause heavier breathing, like singing or exercise. However, “the CDC continues to believe, based on current science, that people are more likely to become infected the longer and closer they are to a person with COVID-19,” it said in a statement. The long-coming update could help to finally clarify the situation after the CDC published guidance acknowledging airborne transmission and then suddenly retracted it last month.
The significance: Evidence that airborne transmission is occurring has been mounting for months; 239 experts wrote an open letter to the World Health Organization in July calling for them to acknowledge it. The WHO still has not recognized airborne transmission as a significant factor in the pandemic, and the CDC’s slowness to do so has caused frustration among aerosol researchers, some of whom say it is the main route for infections. The CDC maintains it occurs only in “limited, uncommon” circumstances. Airborne transmission has become a topic of fierce contention, partly because it makes it far riskier to reopen spaces like restaurants, gyms, bars, schools, and offices.
What do we do now? The CDC advises that people stay at least six feet away from others, wear a mask that covers their nose and mouth, frequently wash their hands, clean high-touch surfaces often, and stay home when they are feeling sick. However, the implications of airborne transmission mean the CDC perhaps ought to shift its emphasis and go further, advising people to properly ventilate buildings, limit the number of people indoors at any given time while encouraging them to stay farther apart and masked, and try to socialize outdoors where possible. “The thing people need to understand is aerosol transmission is like everyone breathing out cigarette smoke, and you want to breathe in as little of others’ as possible. Everyone you are around, imagine they are breathing smoke, and try to avoid it,” Jose-Luis Jimenez, a chemistry professor at the University of Colorado, Boulder, who has studied aerosols for 20 years, told MIT Technology Review in an interview.
Pushback: Jimenez criticized this new CDC update for being written confusingly, using the phrase "small droplets" instead of the widely accepted word "aerosols." Crucially, Jimenez said the document downplays the importance of airborne transmission. "We know that superspreading events are a major component of transmission. And every single superspreading event that has been studied appears to be dominated by aerosol transmission," he said. Jimenez also said that the CDC update appears to suggest airborne transmission from sharing a room together is rare, when it is not. "For example, it is the most likely explanation for the outbreak at the White House," he said.
This story was updated after publishing to include comments from Jose-Luis Jimenez.
Biotechnology and health
The Biggest Questions: What is death?
New neuroscience is challenging our understanding of the dying process—bringing opportunities for the living.
Some deaf children in China can hear after gene therapy treatment
After deafness treatment, Yiyi can hear her mother and dance to the music. But why is it so noisy at night?
Scientists just drafted an incredibly detailed map of the human brain
A massive suite of papers offers a high-res view of the human and non-human primate brain.
Three people were gene-edited in an effort to cure their HIV. The result is unknown.
CRISPR is being used in an experimental effort to eliminate the virus that causes AIDS.
Get the latest updates from
MIT Technology Review
Discover special offers, top stories, upcoming events, and more.