Midday sunlight could deactivate up to 90% of coronavirus strain - study

The study authors say that the higher doses of ultraviolet radiation that occur during midday sunlight act as a "virucidal agent" for the coronavirus.

Sun penetrating the clouds above the mountains near Chengdu, China. "It looks like Genesis to me," says Tomer (photo credit: TOMER ZADOK)
Sun penetrating the clouds above the mountains near Chengdu, China. "It looks like Genesis to me," says Tomer
(photo credit: TOMER ZADOK)
Just around 34 minutes of sunlight can deactivate up to 90% of SARS-CoV-2, the novel strain of the coronavirus, according to a study entitled Estimated Inactivation of Coronaviruses by Solar Radiation.
The study authors, public health researchers Jose-Luis Sagripanti and C. David Lytle, say that the higher doses of ultraviolet radiation that occur during midday sunlight act as an effective "virucidal agent" for the novel coronavirus.
"This notion is supported by the correlation found in Brazil between increased influenza incidence in hospital admission records and solar UV-blocking by smoke during the burning season," the study authors wrote.
The new study focuses on the aspect of viral transmission through surface to surface contact, as well as what a person's exposure to sunlight can do to affect the viral spread and the prevalence of the virus within the body.
"It is well known that there is direct transmission of infectious virions by inhalation of contaminated aerosols exhaled, coughed, or sneezed from infected persons, allowing for little time and opportunity for environmental viral inactivation, unless the virions settle on some surface."
Within the study, the researchers compared genomic UV characteristics of SARS-CoV-2 against other coronaviruses and viral compounds that share similar nucleic acid composition.
"Considering that SARS-Co V-2 is three-times more sensitive to UV than influenza A, it should be inferred that sunlight should have an effect on coronaviruses transmission at least similar to that previously established for the evolution of influenza epidemics," they said.
"If the limited role of relative humidity and temperature (within the range encountered in the environment) reported for influenza A parallels that for SARS-CoV-2 then, the effect of artificial and natural UV radiation on SARS-CoV-2 inactivation should be preeminent," the authors continued, clarifying. "The preeminent effect indoors of germicidal UV (UVC, 254nm) radiation is clearly confirmed by a report whereby inactivation of air-borne virions by UV radiation virtually prevented the spread of influenza among patients in a veterans hospital, during the same time that an epidemic of influenza ravaged similar patients in nearby non-irradiated rooms."
For their analysis of the novel coronavirus pandemic, the authors used the data from the World Health Organization (WHO) and the Johns Hopkins’ Center for Systems Science and Engineering as a basis for a statistical examination of which countries experienced the highest infections per million inhabitants.
Within that, they noticed 28 of the 30 countries reporting the highest infection rates were experiencing colder weather during December-March, when the coronavirus spread was most prevalent, and all them were located north of the Tropic of Cancer.
While they do note the obvious inaccuracies that would occur in these data sets due to the lack of available testing, conflicting numbers of infected travelers, and "vast differences" on country by country response to the global pandemic, they did find consistencies in the data within countries that rest in northern latitudes where exposure to sunlight was limited by the cold weather months in comparison with countries in southern latitudes that had access to abundant sunlight exposure.
In line with this notion, the authors took to note that the lockdowns within each country may adversely contributed to the success of the viral spread, notably with people who live in a multi-person household.
"If we accept a possible virucidal role of sunlight during coronavirus pandemics, then forcing people to remain indoors may have increased (or assured) contagion of COVID-19 among same house-hold dwellers and among patients and personnel inside the same hospital or geriatric facilities," they said.
Adding that "in contrast, healthy people outdoors receiving sunlight could have been exposed to lower viral dose with more chances for mounting an efficient immune response. This argument supports considering the results of two opposed containment approaches to deal with the COVID-19 crisis." 
While the two researchers concluded that sunlight in effect can deactivate a great portion of the SARS-CoV-2 strain, they do note that surface to surface contact and a person's outside exposure is where the bulk of their study is focused.
Cory Merow, co-author of Seasonality and Uncertainty in COVID-19 Growth Rates, noted that the summer months won't have an effect on the coronavirus spread and that social distancing and precautionary measure should still be followed.
“If everybody sits next to one another on the bus and coughs,” Merow told The New York Times. “Ultraviolet light is not going to protect you.”
MIT also supported this claim in a study noting environmental effects on the coronavirus will likely have no bearing on its spread throughout the US and Europe, earlier this year.