While most virologists and epidemiologists have long hypothesized that summer should at least subdue the worst of COVID-19’s transmissibility, recent case spikes in places like Arizona, Florida and Texas are making it clear that the warmer summer season itself will not completely eliminate or even pause the virus from spreading.
Corornavirus case spikes in those states, along with other warm weather locations across the country, have been accelerating since the start of June. While most epidemiologists generally believe that higher temperatures and humidity levels help reduce transmission rates, the virus isn’t simply disappearing in the warmer summer weather.
“At this point, we need to do more in understanding the underlying determinants of spikes — and these are complex including individual, population, and environmental determinants similar to other respiratory viruses,” said Dr. Stefan Baral, an epidemiologist at Johns Hopkins University who has studied the links between the virus’ spread and environmental factors. “But yes, I still do think that an element of this has to do with environmental conditions.”
To be clear: it’s not the warmer weather itself that’s boosting transmission rates and cases. But warmer summer weather is also not serving as the pause button for the virus’ spread that some had hoped it might be. Social distancing measures have gradually relaxed in many states and throughout the country and that, more than anything else, is likely behind the recent uptick in cases in places like Arizona, Texas and Florida.
“We need to do everything we can right now to slow the spread of this disease, and that means we need to follow the advice that public health experts are telling us and practice social distancing and good hand hygiene, among other actions,” said Dr. Aaron Bernstein, the Interim Director for The Center for Climate, Health and the Global Environment at the Harvard T.H. Chan School for Public Health, in a detailed look at links between climate, climate change and the spread of coronavirus.
The spike in cases crosses several other meteorological parameters as well: more humid places, like Florida, are seeing spikes similar to those in hot and dry places, like Arizona and Utah. In other words, the virus has spread in hotter, colder, more humid and less humid locations, perhaps proving that environmental conditionals alone won’t stop the virus’ spread.
That said, researchers continue to believe that colder and drier weather does increase the virus’ transmissibility, generally making it more seasonal and similar to the flu in that sense.
“Thus far, I have not seen any substantial data to refute our hypothesis that low temperatures and specific humidity lead to increased risk of transmission,” said Dr. Mohammad Sajadi, an associate professor of human virology at the University of Maryland, who has extensively studied links between the spread of coronavirus, latitude and weather. “We think the data shows that (COVID-19) is behaving as a seasonal virus, with the spread of it being aided by low temperature and specific humidity.”
But one thing has become abundantly clear in recent weeks: despite widespread hopes that summer would create at least a pause in the virus’ spread, it simply hasn’t. Hotter and more humid weather may be more effective in limiting the virus’ spread, but it’s become clear in recent weeks that it doesn’t completely eliminate it.
“At a certain point, unless strict public health measures are implemented and followed, the healthcare system still gets overwhelmed,” said Dr. Sajadi.
