Coronavirus Spread Probably Won't Be Slowed Down by Warm Summer Weather in America, Study Suggests

Warmer temperatures in the summer likely won't make much difference to the spread of the coronavirus which causes COVID-19 in the U.S., according to a study.

While it is known that the flu is seasonal, it's unclear whether the coronavirus that emerged from the Chinese city of Wuhan late last year will follow a similar pattern, said the authors of the paper published on Clinical Infectious Diseases. So far, tests in labs suggest it can't withstand high temperatures or ultraviolet light, they said.

To find out if temperature, precipitation, and UV light affected the spread of the coronavirus in the U.S., the team noted the daily weather patterns in fifty states and Washington, D.C. between January 22 and April 3, 2020. Based on the incubation period of the disease, they compared these figures with data on cases in these locations five days later.

On average, the daily temperature was 50 degrees Fahrenheit. A daily maximum temperature of greater than 52 degrees Fahrenheit was linked with a statistically significant lower rate of coronavirus five days later. In contrast, there were higher rates when the maximum temperature was 30 degrees Fahrenheit or less.

Higher UV levels were associated with a lower rate of new infections after five days, perhaps because the rays disrupt the integrity of the virus, according to the scientists. They found no link between rain and COVID-19 cases.

The team also used the data they collected to model how hypothetical states would fare. They predicted a state with a maximum temperature less than 52 degrees Fahrenheit would have 23 cases per million more each day at the peak of the epidemic compared with another with a maximum temperature above 52 degrees Fahrenheit.

A state where the temperature kept below 30 degrees Fahrenheit would see around 110 more cases per million at the peak versus a state where the mercury didn't drop below 60 degrees Fahrenheit. These forecasts stuck even when the team accounted for factors which can affect case rates, including population density.

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People are seen practising social distancing in white circles in Domino Park, during the Covid-19 pandemic on May 17, 2020 the in Brooklyn borough of New York City. JOHANNES EISELE/AFP via Getty Images

The authors acknowledge their study was limited in a number of ways, including the possibility that the measures to contain the virus may have skewed the data. For instance, states with warmer climates may have tried harder to contain the virus. In addition, looking at temperatures at a county level would have provided more accurate results, they said.

In their conclusion, the team said: "There is an association between temperature and rate of transmission of SARS-CoV-2 virus which may result in modest decline in the community transmission of SARS-CoV-2 with warmer weather. This effect is modest, however, and is unlikely to slow down disease spread if containment measures are relaxed."

Co-author Dr. Shiv T. Sehra, Assistant Professor of Medicine at Harvard Medical School, said in a statement: "While the rate of virus transmission may slow down as the maximum daily temperature rises to around 50 degrees [Farenheit], the effects of temperature rise beyond that don't seem to be significant.

"Based on our analysis, the modest association suggests that it is unlikely that disease transmission will slow dramatically in the summer months from the increase in temperature alone."

The study is the latest to explore how the environment may affect the little-understood coronavirus which has infected more than 6 million people. Last month, the authors of a paper published in The Journal of Infectious Diseases found sunlight appears to inactivate the virus.

Emeritus Professor Ron Eccles of the U.K.'s Cardiff School of Biosciences, an expert on the nose and upper airways, told Newsweek at the time: "It has been known for many years that UV light inactivates viruses and bacteria and UV light has been used to help sterilize hospital operating theatres when not in use.

The new knowledge is that UV light of the intensity seen on a sunny beach does inactivate viruses such as SARS COV-2 and this is important as it means we are safer outside than in any indoor public spaces.

"'Stay at home' should be replaced with 'stay outdoors in the sunshine but use suncream and keep your distance from others as viruses can still spread from coughs and sneezes.'"

The graphs by Statista below illustrate the spread of COVID-19 cases across the U.S. and around the world.

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