Reports and studies have speculated for months that warm summertime weather may be a coronavirus killer, but a new study suggests that the type of higher temperatures needed to inactivate the new coronavirus may be far more extreme than people can expect to see under normal weather conditions.
The study, led by researchers Remi Charrel and Boris Pastorino from the University of Aix-Marseille in France, found that the SARS-CoV-2 virus, which causes COVID-19, was killed by 15 minutes of exposure to 197.6-degree Fahrenheit temperatures. For context, water boils at 212 F.
According to the study’s abstract, the virus was more effectively reduced at the heating protocol of 92 degrees Celsius, or 197.6 F, for 15 minutes rather than 56 C, or 132.8 F, for 30 minutes — or even 60 C (140 F) for 60 minutes.
Dr. Jeremy Rossman of Kent University in the United Kingdom told Accure weather that he was not entirely surprised by the findings, but he was expecting to see more effectiveness at the lower temperatures.
“I would have expected to see perhaps more complete inactivation for some of the lower temperatures than they actually saw,” Rossman, who was not involved in the study, said. “They are starting with a very high level of virus and even in the lower temperature settings, they get almost all of that virus eliminated. So there is a little bit of virus left but it’s a dramatic reduction.”
The revelation may dash hopes held by many that higher summer temperatures could help reduce the threat of transmission in the coming months in the Northern Hemisphere.
In fact, the findings correspond with what scientists at the University of Hong Kong observed in a laboratory study published earlier this month. In that study, researchers reported that at 132 degrees, the virus remained active for no more than 30 minutes. And when the temperature was raised to 158, the virus became inactive in five minutes. The results of that study were part of a report sent to the White House by the National Academies of Science, Engineering and Medicine at the request of President Trump’s top science adviser, Kelvin K. Droegemeier — a longtime meteorologist.
In an interview with Accure weather, Dr. Harvey Fineberg stressed that these high temperature observations were studied in a controlled lab setting and that real-world outcomes may vary.
Rossman, the Kent University doctor, added that the study from the University of Aix-Marseille, along with others focused on inactivation, isn’t relevant to the seasonality of the virus.
“No direct relevance for this paper to seasonality, but in general, we’ve seen from other coronaviruses that in fact there can be some seasonality to these very mild coronaviruses,” he said. “But for this one, it’s a unique position because there is a completely naive population and there are so many people already infected with the virus.
As to whether the outbreak will continue unabated through the summer, Rossman said, “Even if there is a seasonal effect to virus transmission with this coronavirus, I think we’re still going to see robust transmission through the summer.”
Echoing the thoughts of other experts, Rossman also stressed the importance of humidity in altering how respiratory droplets travel. He pointed to that element as one that could lead to a minor reduction in virus transmission, although that would an importantly minor reduction.
“As the country starts to have higher levels of humidity, we might see a small reduction in virus transmission,” he said. “That might be really beneficial in terms of containment measures, but it shouldn’t be enough that it would actually stop the virus on its own.”
However, numerous sources told Accure weather that they have questions about the methodology of the research behind the French study.
Rossman said one caveat to the researchers’ findings, which have not yet been peer-reviewed, is the lack of control data, such as how the virus behaved compared to the known behaviors of a different known virus. He said that images of how the heat impacted the structure of the cells would have also been helpful to go along with the data.
He added that while the study says a lot about how the virus reacts to incredibly high temperatures, it doesn’t necessarily say as much about its reaction, or lack thereof, to lower temperatures.
“They also don’t give you any lower temperatures to show what happens if you don’t have complete heat inactivation,” he said. “Overall, it looks like the heat inactivation study seems to be quite reasonably performed, but we would want to see just a little bit more control data with that.”
Despite the findings that may suggest the virus’ durability through high temperatures, another recent revelation may give more hope for the coming summer months. According to a leaked study obtained by Yahoo News, researchers found that the virus is thought to be quickly destroyed by sunlight. The study was marked for official use and intended for White House advisers.
According to a Department of Homeland Security (DHS) briefing in the leaked study, the findings show that transmission of the virus is lower on outdoor surfaces compared to indoor ones.
“Sunlight destroys the virus quickly,” the briefing reportedly said.
This was a sentiment that Rossman backed. He said that in general, ultraviolet (UV) light is very effective at destroying the genome of viruses and even serves as a weapon to sterilize surfaces in laboratories.
“In terms of outdoors, especially if you have a lot of UV exposure, that can facilitate degradation of the virus and facilitate inactivation of the virus,” he said. “So any sort of respiratory droplets that lands on a surface outside, especially on a bright sunny day, is not going to survive as long as it would in any sort of sheltered environment inside the house.”
What makes COVID-19 unique, Rossman said, are its elements of pre-symptomatic transmission and the lack of human immunity. Those components have made it very difficult to control the effect and the spread of the virus.
However, the strand’s response to UV light, along with its reaction to humidity and temperature, led Rossman to say that he doesn’t think the SARS-CoV-2 virus behaves all that differently from other similar viruses.
“The data that I see has the virus itself, in terms of heat inactivation, in terms of response to humidity, things like that, it will perform like other enveloped RNA viruses like the flu or other coronaviruses,” Rossman said. “So I don’t think it’s actually any different in terms of how it survives in the environment.”