• Coronavirus transmission is apparently greatly helped in humid weather conditions.
  • That’s according to a new study analyzing the ability of the COVID-19 coronavirus to spread in droplets more easily outdoors when the weather is humid. In fact, this new study suggests that such droplets can live up to 23 times longer in humid air.
  • We still, however, have so much more to learn about the virus, which according to Johns Hopkins University has been responsible for more than 5.5 million infections in the US, as well as almost 173,000 deaths.

The Trump administration’s COVID-19 testing czar has some positive news about the overall direction of the coronavirus pandemic in the US, telling reporters that cases are down more than 20% from July and that “trends are going in the right direction.” That’s according to Adm. Dr. Brett Giroir, per CNN, who spoke during a US Department of Health and Human Services briefing on Wednesday, stressing that basic steps like social distancing, regular hand washing, and wearing a face mask “continues to yield results.”

That’s not to say, however, that we’ll be able to ease up on any of the protective measures and public health guidance offered in response to the pandemic anytime soon. For evidence of why that’s the case, look no farther than to the news that keeps piling up regarding how the task of reopening schools around the country is so fraught with peril. It’s why we keep seeing stories like this one, involving almost 2,000 K-12 students in Mississippi having to be quarantined in the state as a result of being possibly exposed to the coronavirus. Meanwhile, we’re also learning more about coronavirus transmission, thanks to a study published this week in the journal Physics of Fluids.

Basically, the researchers behind that study found that when respiratory droplets potentially infected with coronavirus are expelled — such as when a person coughs — those droplets can live up to 23 times longer than they otherwise would when the air is extremely humid. “It should be emphasized that the humidity can extend the airborne lifetime of a 50 (micron) droplet by more than 23 times,” the study’s authors note. “This suggests that the airborne transport of median-sized droplets is extremely sensitive to the humidity.”

When air is completely dry, however, the study explains that a 50-micron droplet evaporates within 1.7 seconds.

“If the virus load associated with the droplets is proportional to the volume, almost 70 percent of the virus would be deposited on the ground during a cough,” study author, Binbin Wang, PhD, said in a news release about the findings. “Maintaining physical distance would significantly remediate the spread of this disease through reducing deposition of droplets onto people and through reducing the probability of inhalation of aerosols near the infectious source.”

The study did not focus specifically on droplets infected with coronavirus, rather droplets in general. It’s well-understood, however, that respiratory droplets from someone infected with coronavirus even if they’re not showing symptoms can be flooded the virus, and this study makes clear that those particles may linger in the air much longer in humid temperatures when they otherwise might fall much more quickly to the ground.

Andy is a reporter in Memphis who also contributes to outlets like Fast Company and The Guardian. When he’s not writing about technology, he can be found hunched protectively over his burgeoning collection of vinyl, as well as nursing his Whovianism and bingeing on a variety of TV shows you probably don’t like.