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Can summer sun kill coronavirus? Study claims it inactivates 90%

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A new study claims that summer sunlight at high noon can kill up to 90 percent of coronavirus in most US and international cities within 34 minutes. 

The study authors – a pair of retired US government scientists, one of whom worked for the Army and a second who worked for the Food and Drug Administration (FDA) and National institutes of Health (NIH) – believe that lockdowns may have actually done harm to citizens who were not exposed to virus-inactivating sunlight. 

Their article, published in the journal Photochemistry and Photobiology, is among a growing body of evidence that suggests coronavirus may in the cold and fares more poorly at higher temperatures and humidity.   

And ultraviolet light – the same radiation the sun emits – is now being used to sterilize surfaces, including New York City subways. 

But while many scientists contend that the dose of UV light needed to kill coronavirus is unsafe for humans and that summer heat may slow but not stop the pandemic, Dr Jose-Luis Sagripanti and Dr C David Lytle insist the sun will keep us safe. 

It echoes President Trump’s assurances that warm weather would drive away coronavirus outbreaks. 

But two experts told DailyMail.com that, while the research is interesting, the lab-based data is unlikely to translate directly to the real world, and sunshine is unlikely to save us from infection this summer.

The debate over how heat affects coronavirus rages on in the US. One study claims summer sunlight can kill 90% of the virus, but two experts say that will do little to stop transmissions

The debate over how heat affects coronavirus rages on in the US. One study claims summer sunlight can kill 90% of the virus, but two experts say that will do little to stop transmissions

‘There’s a little scientific truth there, but it’s not the kind of truth that’s going to make a difference to the infection rate,’ Texas A&M University Texarkana biologist Dr Ben Neuman told DailyMail.com. 

 Sunlight, he said, ‘will clean up some of the virus that’s going to be laying around, but it’s in the stuff that comes out of someone’s mouth, hangs briefly in the air, and goes right into someone else’s nose or mouth.’ 

Dr Neuman, most of whose research is specifically on coronaviruses, explained that UV rays can kill naked virus, but are much less effective at inactivating the virus when it is in droplets of mucus from infected people’s noses or mouths.  

The researchers behind the new study used data from exposures of the virus to UV light in labs and ran them through a model that was made for ‘biodefense’ purposes to estimate how sunlight would affect various viruses. 

According to their estimates, the virus could stay infections for a day or more between December and March in ‘most cities.’ 

But in the summer, 90 percent or more of the virus would be inactivated – meaning that it would no longer be infectious – within just 11 to 34 minutes of midday sunlight in the summer months, they estimate. 

They also speculate that this would hold true in many cities throughout the world (but do not specify which ones). 

To bolster their argument, the researchers point to the trends in the virus’s spread in various parts of the world over the past six months. 

‘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 during the same period, suggests an environmental role for sunlight in the COVID-19 pandemic,’ they wrote. 

Florida's temperatures are now well above those that most studies suggest coronavirus thrives in, but cases are spiking in the sunshine state, where more than 100,000 people have tested positive. Pictured: beachgoers in Clearwater, Florida on May 4

Florida’s temperatures are now well above those that most studies suggest coronavirus thrives in, but cases are spiking in the sunshine state, where more than 100,000 people have tested positive. Pictured: beachgoers in Clearwater, Florida on May 4 

Dr Sagripanti and Dr Lytle are not the first to observe this patten. 

Scientists at the University of Maryland School of Medicine published a study in JAMA Network Open demonstrating the narrow ‘band’ of cities where coronavirus spread like wildfire between November and March (although it wasn’t necessarily present in all eight of the cities they looked at for the duration of that time period). 

From November 2019 to March 2020, the eight cities that had substantial spread were all within a narrow band of latitudes between 30° N and 50° N.

Results showed that in January 2020 in Wuhan and in February 2020 in the other seven cities, the average temperature at airport weather stations was between 39F (4C) and 48F (9C).

Average temperatures 20 to 30 days before the first death resulting from the virus’s spread in each city were roughly the same, ranging from 37F (3C) to 48F (9C).

However, COVID-19 was unsuccessful in spreading as widely among cities north of this band such as in Moscow, Russia, which sits at 56.0° N, and south such as in Bangkok, Thailand, sitting at 13.7° N.  

‘We think that the virus is behaving like a seasonal respiratory virus,’ Dr Mohammad Sajadi, an associate professor at the Institute of Human Virology at the University of Maryland School of Medicine, told DailyMail.com in a recent interview.

‘What this means is that the virus has temperature and humidity requirements that aid in its transmission.’ 

Based on experiments exposing coronavirus and seasonal influenza to UV light, Dr Sagripanti and Dr Lytle estimate that SARS-CoV-2, which causes COVID-19, is about five times more sensitive to sunlight flu. 

Experts say that being close to other people will determine your risk, not the weather. Pictured: Beachgoers sunbathe at Miami Beach without face masks or social distancing

Experts say that being close to other people will determine your risk, not the weather. Pictured: Beachgoers sunbathe at Miami Beach without face masks or social distancing 

That would suggest that coronavirus’s activity levels would fall even lower than flu during the summer in the US, when the country gets the most direct and potent sunlight. 

Indeed, as summer has begun in the US, the original hotspots – cities like New York and Seattle, which fall into the ‘band’ of vulnerability identified by the University of Maryland team, have seen new cases and deaths slow. 

And Brazil, which is entering its winter, has seen a surge in cases in recent weeks, suddenly becoming the second hardest hit country in the world. 

But these are just observational links.  

‘The virus grew at the same rate in Ecuador on the equator as in Iceland, which is cold,’ said Dr Neuman.

In Brazil, temperatures rarely fall below 68. In the US, states like Arizona and Texas are hitting record highs. Daily high temperatures those states average around 100 or 90 degrees F in June.

‘Now [the virus] is in the sunbelt of the US, in Arizona, Texas and Florida – you can’t tell me those people don’t get a lot of sunlight,’ Dr Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco (UCSF).

The new study is documenting ‘a lab phenomenon,’ he asserts.

He echoed Dr Neuman’s sentiments, saying: ‘All these models are really cool and interesting, but probably not that relevant right now.’

When the virus is less prevalent in communities, heat may have some marginal effect on ‘cleaning up’ spare virus in the environment.

But even if it’s seasonal, like the flu, that doesn’t necessarily mean that summer and high temperatures have anything to do with the peaks and valleys of coronavirus outbreaks.

Dr Neuman notes that most viruses – such as polio and HIV – are not seasonal and it’s not clear what makes flu and coronavirus seasonal, and it may not be explained by climate.

‘The fact is we don’t know,’ he said. 

‘Coronaviruses also have a season, but it’s shifted off by about three months and they’re often around in the spring, but there’s no reason or rhyme. ‘ 

Both scientists agree that whatever the effect of sunlight, nothing can currently replace social distancing and mask-wearing.  

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