Memorial Day is ushering in summer and hopes that warm, humid weather will take a bite out of coronavirus transmission, though scientists warn it won’t be a panacea as Americans flock to beaches, public pools and parks.
Other viruses exhibit seasonal patterns in which transmission slows in warmer, wetter months before returning in the fall and winter. Droplets that carry the disease tend to drop to the ground faster in the humidity instead of remaining airborne.
The White House also showcased evidence the new virus fares poorly on surfaces in direct sunlight and hot weather.
Still, the pathogen has been able to spread in warm environments from Brazil to Singapore, prompting experts to preach caution as beach-combers migrate to shorelines and BBQ parties beckon. One of the glaring problems is that since this coronavirus is new to humans, no one has natural immunity to it.
“We project that warmer or more humid climates will not slow the virus at the early stage of the pandemic,” Rachel Baker, a postdoctoral research associate in the Princeton Environmental Institute (PEI), said in a release on a university study published May 18. “We do see some influence of climate on the size and timing of the pandemic, but, in general, because there’s so much susceptibility in the population, the virus will spread quickly no matter the climate conditions.”
The pandemic is entering a critical phase, with states beginning to reopen as “social distancing” flattens the curve of transmission.
The Centers for Disease Control and Prevention advised swimming areas to encourage social distancing, such as arranging decks so chairs are at least six feet apart, or introducing pool lanes and using signs and tape to maintain spacing.
Managing beach-goers could be a bit more difficult.
“They’ve never had to manage flows of people this way,” said Joseph Allen, an assistant professor of exposure-assessment science at Harvard T.H. Chan School of Public Health. “Pretty much, when you get on the beach everyone just finds a spot.”
“It’s very haphazard where people are working past each other, through each other, and so it could be done in a more choreographed manner,” he said, suggesting cordoned off beach lanes for people to come and go.
He said people inside of buildings or offices should open windows and allow fresh outdoor air to flow through when they can this summer, citing the “unlimited dilution” of virus particles.
“We know that the virus doesn’t survive long on surfaces in the presence of natural light, so we get some benefits from being outdoors,” he said.
U.S. coronavirus coordinator Deborah Birx said Friday it would be fine for people to head out and enjoy themselves on Memorial Day, but they should stick to the outdoors and maintain distance from others.There are other precautions they can take, too, such as playing tennis or other sports with marked balls so they only touch their own equipment.
Florida Gov. Ron DeSantis highlighted the benefits of outdoor activity in a business roundtable with Vice President Mike Pence last week. He said his state hasn’t seen a big outbreak related to outdoor leisure, noting it is unlikely that golfers would get the virus from touching a flagstick on the course.
“Honestly, if I touch it and I have the virus, and you’re in the group behind me, 10 minutes later, the sun’s gonna nuke that,” Mr. DeSantis said.
“This is a virus that just doesn’t transmit as well outdoors, in outdoor open-air environments,” he added. “It likes the enclosed spaces.”
Some scientists say while virus will not disappear completely in warmer weather, it tends to thrive in specific conditions.
Dr. Anthony Amoroso, an assistant professor of medicine at the University of Maryland, has been tracking weather forecasts to determine the optimal temperature and other factors for transmission of COVID-19, the disease caused by the new coronavirus.
They’ve found that it does best in temperatures of 41 to 51 degrees Fahrenheit with a specific humidity of 3 grams of vapor per 6 kilograms of air and absolute humidity of 4 grams of water vapor per 7 cubic meters of air.
He said Maryland appeared to reach its tipping point around May 17, while by the end of the month, much of the country is set to be warm enough to present less favorable conditions for the virus.
“Based on calculations, in the mid-Atlantic states by the week of May 24-31, only Boston will have a small probability of optimal temperature for transmission during that week,” Dr. Amoroso said.
Scientists are closely monitoring the virus in Southern Hemisphere countries to see how the virus behaves in colder months and sustains itself in the human population.
Federal officials have warned that a second wave of transmission in the fall and winter would coincide with challenges from flu season.
“We all need to heed that very carefully. If a second wave of COVID comes this fall, along with seasonal flu, it could really complicate the public health landscape even more,” said Howard Koh, a professor at the Harvard T.H. Chan School of Public Health. “That’s why a national plan, now, to be much more proactive about all of this is critically important.”