It's the first week of summer, and despite rumors and proclamations from some public figures, the coronavirus is still here despite the warmer weather.
As summer plans adjust to a growing pandemic, it's important to understand why people still need to take caution against COVID-19.
Many infectious diseases are seasonal, so it's not unreasonable to wonder if COVID-19 could be as well. Flu famously begins to increase in the fall and spike in the winter. When polio was still a widespread disease, the worst outbreaks were in the summer. But understanding why a disease is seasonal can be hard work.
Popular culture started to associate polio outbreaks with summer swimming after Franklin Roosevelt caught the disease on vacation, but chlorine would kill the virus in the water. Widespread vaccination banished polio from most of the world before the cause of polio season was understood.
The cause for the flu season is still not fully understood. Some doctors attribute it to human behavior, as people spend more time closer together indoors in colder weather. Other theories suggest the weather causes important physical changes.
For instance, studies show flu viruses are more easily spread in colder, drier air. But there's some doubt over whether this is because of a trait of the flu virus or because the lungs may be more vulnerable to infection in those conditions. And in tropical environments, flu is actually a year-round disease, and may spread more easily in moist air.
Some early studies on the coronavirus responsible for COVID-19 saw that, like the flu virus, it does have a harder time surviving in hotter, wetter environments. But this doesn't make it much safer to gather closely with other people, according to Timothy Sheahan, a virologist at the University of North Carolina at Chapel Hill.
New studies show breathing in the coronavirus is the main way it spreads, and touching contaminated objects is less likely to infect someone. If two people are close together, breathing in the same air, it doesn't give a hot day much time to kill the virus.
This is also the problem with sunlight. While it's thought that ultraviolet, or UV, light can kill the virus, a sunny day won't stop COVID-19. The most energetic kind of UV light that could kill the virus in a short amount of time is also the UV light most blocked out by the atmosphere.
While hospitals and labs use specialized UV light sources to sterilize equipment, they're very powerful compared to daylight. "If you shined that light on your skin, you'd get torched," Sheahan said.