Summer rays can inactivate coronavirus in 34 minutes, study says

Midday sunlight is capable of inactivating 90 percent or more of the SARS-CoV-2 virus after 34 minutes of exposure, a recent study found.

Study authors calculated the expected inactivation by UVC and solar UV radiation in cities around the world at different times of the year. They concluded SARS-CoV-2 should be inactivated “relatively fast” during summer in many populous cities worldwide, pointing to the role of sunlight in the occurrence, spread rate, and duration of coronavirus pandemics.


Jose-Luis Sagripanti and C. David Lytle wrote the study, which was published in the journal Photochemistry and Photobiology earlier this month. The scientists are retired from the US Army and Food and Drug Administration, respectively, the New York Post noted.

Further, they found only Miami and Houston get enough solar radiation to inactivate 99 percent of the virus in the spring. During winter, most cities will not receive enough solar radiation to produce 90 percent viral inactivation during midday exposure, they wrote.

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From December until March, "the virus will persist infectious for a day or more in winter, with risk of re-aerosolization and transmission in most of these cities," the study found.

The two authors conducted their calculations using a model for estimating solar inactivation of viruses of biodefense concerns, they said, adding that the methodolgy was validated with Ebola and Lassa viruses.

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If sunlight plays a possible destructive role of the virus, authors theorized stay-at-home orders forcing people to remain indoors might have increased contagion among members of the same households.

"In contrast, healthy people outdoors receiving sunlight could have been exposed to lower viral dose with more chances for mounting an efficient immune response," they wrote.