Why getting COVID-19 at an indoor gathering is even likelier than experts once thought
Colder weather is driving people indoors, where the coronavirus is revealing unrecognized transmission risks.
Celebrating the holidays at one or two smallish indoor gatherings of relatives and friends wouldn’t be that risky, right?
As much as we all want to rationalize venturing beyond our pandemic pods, the risk is even greater than experts originally thought.
The latest study to reveal the insidious infectiousness of the coronavirus comes from South Korea. A high school student was infected after five minutes of exposure to a contagious person with no symptoms — who was sitting 20 feet away in the air-conditioned restaurant. They weren’t wearing masks but had no direct or indirect contact, such as touching the same plate or doorknob.
The researchers, who published their findings in the Journal of Korean Medical Science, used data from South Korea’s aggressive contact-tracing program, combined with investigative methods worthy of TV’s CSI detectives.
The South Korean study adds to mounting evidence that the coronavirus can be transmitted in microscopically small droplets that are released by talking or just breathing, then stay aloft indoors, traveling long distances with the help of air conditioners, fans, or drafts.
“Droplet transmission can occur at a distance greater than [6 feet] if there is direct air flow from an infected person in an indoor setting,” wrote the researchers from Jeonbuk National Medical School.
The study also undermines now-ingrained principles for staying safe. It suggests that even if you keep six feet of social distance indoors, and keep closer interactions to less than 15 minutes, you could be infected. Masks lower the risk, but not to zero.
“I think this is an interesting and important case study that continues to support the idea that the 15-minute/6-foot metric lacks strong justification, and that exposures beyond those limits can still be consequential,” said Charles Haas, an environmental engineering professor at Drexel University.
Six feet is not magic
So why did the six-feet rule of thumb become a mantra for public health authorities worldwide?
It is based on the assumption that the coronavirus spreads primarily in big droplets released by a cough or sneeze. It is also based on outdated studies that found most large infectious droplets fall to the ground within six feet, or about two meters. An influential 1942 study used high-speed photography to capture this phenomenon.
“However, the technology was insufficient to catch smaller droplets,” a team of British and American researchers wrote in a paper published in June by the Centre for Evidence-Based Medicine. “These earlier studies also used methods that lack accuracy, particularly with respect to air sampling.”
The authors called the social distancing rule “an over-simplistic picture of viral transfer” that assumes a clear difference between large globs and microscopic ones, called aerosols, that can waft invisibly through the air, like pollen.
“Most public health professionals have been clear for months that there is nothing magic about six feet,” University of Michigan epidemiologist Ryan Malosh wrote in October in the Conversation. “In the same way, there is nothing magic about 15 minutes. These should be used as rough estimates to indicate the types of contact that are relatively higher risk.”
The World Health Organization and the U.S Centers for Disease Control and Prevention have been slow to come around to this more complex view of transmission, one that adds to the challenges of curbing and containing the virus.
It wasn’t until July that the WHO revised its official information on how the coronavirus is spread to acknowledge that airborne transmission of the virus “cannot be ruled out.” The revision came a day after an international group of 239 scientists, including Drexel’s Haas, urged the agency to address the risk.
The CDC didn’t acknowledge the possibility of aerosol transmission until October. That same month, the agency updated its definition of “close contact” to concede that even brief exposures, even with a mask, can lead to infection. Instead of the 15 minutes within six feet metric, the guidance now says spending a cumulative total of 15 minutes with an infected person over 24 hours should be considered close contact.
Masking our vulnerability
Masks have been a crucial, and contentious, precaution in the pandemic.
One clear drawback: You can’t eat while masked. (What fun is a holiday gathering without eating and drinking?)
And while masks do reduce the risk of catching as well as spreading COVID-19, their effectiveness varies widely, as many studies have shown.
The latest one, in JAMA Internal Medicine, found the “fitted filtration efficiency” — the percent of airborne particles that were filtered out — varied from 27% to 79% for cloth masks and improvised face coverings such as bandannas and neck gaiters.
The study found medical procedure masks — the type with accordion fabric and elastic ear loops — were about 39% efficient. But when modified with extra loops to make them fit tighter, they were up to 80% efficient. High-grade, government-certified medical masks, called N95s because they are supposed to filter out 95% of particles, lived up to their name.
Even with a good mask, you still have to breathe. So if you are infected with the coronavirus but don’t know it, some of your virus-laden exhalations will escape out of the sides of the mask.
The Washington Post used an infrared camera capable of detecting exhaled breath as a proxy to show potential transmission risk under various scenarios. An infrared video of a woman wearing a mask was particularly, well, breathtaking. It showed plumes of exhaled breath rising from her face covering and engulfing her head.