Why scientists warn the heat of summer won’t be a cure-all for the coronavirus

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WASHINGTON — Scientists are warning that COVID-19 could continue to spread at epidemic levels in the heat of summer despite initial findings from a government study that the novel coronavirus dies quickly in humidity and sunlight.

That study, outlined at the White House by Under Secretary of Homeland Security for Science and Technology William Bryan on Thursday, found the coronavirus survives for mere seconds or minutes on surfaces and in aerosol form when exposed to ultraviolet rays and to heavy humid air.

President Donald Trump expressed hope that the coming summer heat could accelerate an end to national guidelines on social distancing that have brought the U.S. economy to a halt. Vice President Mike Pence said that the heat “could well give us a summer respite” from the virus.

But scientists in Europe who have researched the seasonality of the coronavirus since the outbreak began say those findings only provide limited insight into what to expect of its spread going forward.

“Seasonality will very likely play a big role in the transmission of COVID-19, eventually – but not immediately,” said Sema Nickbakhsh, a research epidemiologist at the University of Glasgow Centre for Virus Research. “The influenza pandemic of 2009 has taught us that even seasonal viruses can spread to epidemic levels during summer months.”

The susceptibility of the virus to heat was expected in the scientific community.

What remains unclear is the extent to which this coronavirus is spread outdoors versus indoors, whether surfaces are a primary source of cross contamination, and how long it will take for individual populations to grow accustomed to the new virus, developing a level of collective immunity.

Those factors – more than the effects of summer – will shape the course of the outbreak, scientists say.

“Higher temperatures accelerate most biochemical processes — that is something that has been researched in the context of influenza for a long time,” said Richard Neher, whose lab at the University of Basel in Switzerland has extensively modeled the effects that changing seasons might have on the outbreak. “We know it has an effect. But we don’t know how far it brings down R naught — the rate of transmission from person to person. That is the level of certainty we don’t have.”

The DHS study took advantage of unique and sophisticated lab tools that enabled its scientists to suspend particles of the coronavirus middair, subjecting them to various temperatures and humidity levels. The study conducted similar research on the coronavirus’ half-life on surfaces.

“Within the conditions we’ve tested to date, the virus in droplets of saliva survives best in indoors and dry conditions,” Bryan said at the daily White House coronavirus briefing. “The virus dies the quickest in the presence of direct sunlight.”

That behavior is consistent with the four endemic coronaviruses that the world lives with today, said Robert Dyrdak, a specialist in clinical microbiology at the Karolinska University Hospital in Stockholm.

At the largest clinical lab in Sweden, Dyrdak and his team reviewed more than 200,000 patient samples collected since 2010 for seasonal behavior patterns of well-known coronaviruses, looking for insight into the current spread.

“It’s reasonable to assume that it will behave similarly because it is the same family of virus: it infects the same organ, upper respiratory infection, and it transmits in the same way,” said Dyrdak. “It’s great if there is a summer effect, because then the effect of the lockdowns is enhanced.”

Scientists in the United States are conducting similar work. In addition to the DHS project, the National Institute of Allergy and Infectious Diseases, led by Dr. Anthony Fauci at the National Institutes of Health, has been supporting research into questions of seasonality.

“NIAID has supported research on the seasonal circulation of coronaviruses,” a spokesperson for NIAID said in an email to McClatchy, pointing to a study that corroborated the findings in Dyrdak’s report on the seasonality of common coronaviruses. “This data could contribute to a better understanding of the SARS-COV-2 coronavirus which causes COVID-19.”

At Harvard University’s T. H. Chan School of Public Health, the Shaham Group at Columbia University and the Gates Foundation, epidemiologists and microbiologists are working together to apply their past work on influenza forecasting to the current outbreak.

But those scientists note that, while the seasonality of viruses has been observed for centuries, the causes are still “poorly understood.”

If heat and humidity were enough to stop the spread, the southern climate of Georgia and Louisiana, the tropical island of Singapore or the southern continent of Australia, which is currently in its summer months, would presumably see fewer cases.

But those regions are experiencing outbreaks “because of population susceptibility,” said Nickbakhsh. “The human population has no prior experience with this new variant of coronavirus.”

“Weather may help to reduce the spread of COVID-19 during the summer,” Nickbakhsh said, “but going by previous flu pandemics, population susceptibility is likely to play a bigger role in enabling its spread at the moment.”

While Trump touted Bryan’s work, he has not addressed the findings of another government paper released earlier this month by the National Academies of Sciences, Engineering and Medicine, questioning the effects heat and humidity will have on the summer spread of COVID-19 throughout the United States.

Asked at the Thursday briefing how he might change federal guidance in light of the DHS report, Trump said: “We’re going to have to see where it is.”

“I’ll tell you one thing,” the president added, “I think a lot of people are going to go outside all of a sudden. People that didn’t want to go outside, they’ll be going.”


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