Why government scientists now say summer heat is not enough to halt virus in Sunbelt

Government scientists are still confident that summer heat, humidity and sunlight make it harder for the coronavirus to spread in the air and on surfaces, but say human behavior is fueling outbreaks across the nation’s Sunbelt.

In an interview with McClatchy, the lead scientist behind a prominent study on the impact of heat and light on COVID-19 said a failure to adequately social distance, resistance to mask wearing and a reliance on air conditioning indoors has contributed to rising cases, despite increased temperatures and humidity.

The Department of Homeland Security scientists behind a sophisticated scientific study – which was presented at an infamous White House press conference in April where President Donald Trump suggested injecting human bodies with light and disinfectant – have continued their research, and since published their data in multiple journals.

“The conclusions are still the same,” said Lloyd Hough, a senior official and biology expert with Homeland Security’s Science and Technology Directorate. “We still see all of the same trends, that when heat and humidity increase, the virus’ stability on surfaces decreases. And then when you expose the virus on a surface or in the air to sunlight, that has an even more rapid effect at killing the virus.”

But hope within the Trump administration that the DHS findings would translate into a lull in the COVID-19 pandemic during summer have been dashed. Cases and positivity rates in Texas, Arizona and Florida have soared in the past month.

Part of the problem, scientists say, is that air conditioned indoor venues, with closed spaces and recirculated air, essentially replicate the winter environments that help viruses spread.

“We know the virus is less stable in the environment in hot, humid and sunny places. But in all of those places, people still spend a lot of time indoors,” said Hough. “The question about why we’re seeing increases in the Sunbelt – where they have a lot of heat, they have a lot of humidity and they have a lot of sunlight – is because this is just one step in the overall chain of events that has to happen in order for somebody to transmit the virus to somebody else.”

Hough said there were three main reasons why the virus has rapidly spread across the South and Southwest in summer, defying the expectations of some – including Trump, who said on several occasions that the virus would go away “with the heat.”

One reason is that scientists still don’t know what concentration of virus – or dosage – is required for someone to get infected after exposure.

“For us right now, the most important question is how much is required to cause an infection. And the sad part is, I don’t think we’ll actually get a good answer,” Hough said. “We just don’t have the tools necessary to really determine what that infectious dose really is.”

But another reason is human behavior: the failure of individuals to socially distance, to wash their hands and to wear masks. He also cited the failure of some public officials to encourage or enforce public health guidelines.

“There’s probably a lot more about the virus and its transmission that is really linked to our behaviors as people in those environments – whether or not we’re maintaining proper social distance, whether we’re wearing a mask or not, whether we’re washing our hands,” he said.

The third reason is that summer heat and humidity is driving individuals to indoor environments, he said, where epidemiologists increasingly agree the virus has an easier time spreading from person to person.

Most air conditioning units, Hough said, recirculate air without filtering out particulate contaminants such as virus droplets.

“We’ve seen evidence of transmission in bars, where again, you’re indoors, you’re probably enjoying the air conditioning – so the temperature is cooler, the humidity is lower, and you’re not exposed to sunlight,” he said.

Since the DHS study – which used rare and expensive equipment to isolate virus particles midair – was announced in April, other research studies in the United States and around the world have been published with similar conclusions.

A Harvard study released in June examined the linkage between air conditioning use – which started earlier in the Sunbelt as temperatures began to increase – and “rebreathed air fraction,” or the amount of air one is exposed to that has been recirculated indoors.

“Suddenly in February and March in the Northeast, when we were all huddled inside, we had a lot of transmission, where in the South they didn’t see it – we’re now all outside and they’re huddled inside due to the heat,” said Ed Nardell, a professor of immunology and infectious diseases at Harvard University’s T. H. Chan School of Public Health and an expert on airborne diseases who authored the study.

“It’ll be really hard to tease out people’s behavioral factors,” he said, “but when you’re inside, there’s no doubt about the behavioral factors.”

Another international study involving scientists in Canada, Spain and Brazil also found that, while heat, humidity and sunlight decrease the life of the virus on surfaces and in air droplets, those factors also drive individuals indoors and into a sense of complacency that the summertime environment serves as a natural protection.

“The higher temperatures depress transmission of the virus outside, but the higher temperatures also push people indoors to environments where spread is easier,” said Antonio Paez, a professor and researcher at McMaster University in Canada who was lead author of the study.

The scientific consensus is increasingly clear that summertime effects decrease the virus’ ability to spread, Paez said.

“But we see these very very high numbers, and it leaves a troubling alternative, that the numbers we’re seeing in some of those states are actually suppressed by the heat and humidity,” Paez added. “We don’t know how it would be if it were colder. Those numbers could actually be higher if not for the heat.”