Summer sun could kill virus in 30 minutes

Research shows warmest week of the year is likely to slow transmission as it decays in strong sunlight

THE hottest week of the year could lower coronavirus transmission rates, as a study showed that strong sunlight causes the virus to decay to almost nothing in just 30 minutes.

Temperatures are forecast to rise above 30C (86F) on Thursday, which could bring crowds to beaches and parks, with Britain hotter than Ibiza.

Although mass gatherings may suggest a rise in transmission, research by retired virologists from the US army and US food and drug administration showed that sunlight quickly kills the virus, meaning people are likely to be safer outdoors.

In fact, being indoors in lockdown may have been harmful for people, the study suggested.

During peak sunshine in London – which occurs during the summer solstice around June 21 – just 30 minutes of sunlight is enough to reduce the infectivity of coronavirus by 90 per cent.

It means that even if someone was infected and coughed or sneezed onto an outdoor surface, the virus would be largely harmless within half an hour, with just a tiny viral load remaining.

The effect of sunlight on the virus is far greater at this time of the year. During the autumn equinox, on Sept 22, it would take an hour and 17 minutes to render the virus largely harmless in the capital, and at the spring equinox, March 20, nearly three hours. At the Dec 21 winter solstice, the virus could survive for more than five hours in the weak sunlight, although indoors it is likely to last for days.

For cities at a more northerly latitude, such as Newcastle, it would take slightly longer for disinfection – around 34 minutes in midsummer, an hour and 40 minutes in the autumn, nearly four hours in spring and more than five in winter.

In the journal Photochemistry and Photobiology, Dr Jose-luis Sagripanti and Dr David Lytle, the study report authors, wrote: “Forcing people to remain indoors may have increased contagion among same household dwellers and among patients and personnel inside the same hospital or geriatric facilities. In contrast, healthy people outdoors receiving sunlight could have been exposed to a lower viral dose with more chances for mounting an efficient immune response.

“The viral persistence estimated here for cities at northern latitudes where Covid-19 expanded rapidly during winter 2019-2020 and relatively higher viral inactivation in more southern latitudes receiving high solar radiation suggests an environmental role for sunlight in the pandemic.”

Sunlight includes ultraviolet radiation which damages viruses’ DNA. They have a fatty protective coating which degrades when it is warm. While the melting of the coating allows the virus to invade the warmth of the body, it dies if the casing disintegrates outside.

A study by the US National Biodefence Analysis and Countermeasures Center also found that coronavirus floating in the air decays by 90 per cent in just six minutes of summer sunshine and 19 minutes of winter sunlight.

Weather maps show a 700-milewide plume of tropical air moving towards Britain. Marco Petagna, of the Met Office, said: “Thirty-four degrees looks a distinct possibility on Thursday.” Brian Gaze, a Weather Outlook forecaster, added: “June has been flaming wet, but will switch to flaming hot.”

During the Spanish Flu pandemic of 1918, doctors found that patients who were nursed outdoors fared better.

A study by Harvard University showed that at 6C in dry weather, flu on a surface survived for more than 23 hours, but at a temperature of 32C, it was dying within an hour. Bright sunlight can quickly heat up surfaces beyond 32C.