Summer arrives and the flu disappears? So no wonder it’s called “seasonal” flu. This appears to be happening with the coronavirus as well. What’s with the sun’s special germicidal power? That’s what the INAF’s physicists will tell us.

About two months ago, we posted about an experiment by the Italian National Institute for Astrophysics (INAF), which posed the question: how can we disinfect both objects and air from the coronavirus, and in an ecological manner? With this question to answer, the researchers thought that UV rays, known for their ability to kill viruses, could help (read more).

A few days ago, the INAF published an article in which the team demonstrated that a very small dose (3.7mJ/cm2) of UV light is sufficient to inactivate and inhibit virus reproduction by a factor of 1000: this practically cancels it out! The necessary dose is equivalent to the dose delivered for a few seconds by a UVC Lamp placed a few centimeters from the target.

Why were these measurements taken?

Although the germicidal power of UV radiation had been known, no one had yet made accurate studies and measurements on the dose(s) needed to inactivate SARS-CoV-2. In addition, until the study by INAF researchers, doses with wildly varying values had been considered to be the result of the heterogeneous studies of other viruses.

This data will be very useful in developing a portable system for the disinfection of everyday objects, and will also be useful to entrepreneurs and public operators in developing systems and processes useful to counter the development of the pandemic.

Since the INAF is highly specialized in physics, for the biological portion, they collaborated with the State University of Milan, the National Cancer Institute (INT) and the Fondazione “Don Gnocchi” (the Don Gnocchi Foundation), which has been able to measure the relative strength of the virus and safely manipulate it, both before and after the administration of UV doses.

Can the sun destroy SARS-CoV-2?

From the results obtained by INAF researchers and collaborators, it’s clear that the sun (and especially its UV rays) can play an important role in reducing the risk of infection over the coming months. Moreover, the increase in temperature also affects the evaporation of the droplets emitted by both exhaling and sneezing, thus reducing their presence in the air.

These two factors; UV rays and air temperature, partially explain why the infection is now developing in the southern hemisphere, now that it’s facing winter, while the northern hemisphere in which we live sees the opposite effect. Certainly, there are other factors that contribute, including the evolutionary adaptation of the virus to its host (i.e. to humans), and also the various containment measures.

An observation which goes against this hypothesis stems from the fact that, for example, in countries such as Saudi Arabia where the sun is very strong and the temperature is high, the infection rate is still growing sharply, with about 4,000 cases (data as of June 18, 2020). An anomaly for which researchers still have no plausible explanation.

The study conducted by the INAF and the University of Milan, is in-line with the model of the U.S. Army’s Medical Research Institute of Infectious Diseases (USAMRIID), that tries to explain the seasonal pattern of certain viruses, such as flu viruses.

This model takes into acount UVB and UVA rays reaching the Earth’s surface, as opposed to UVC rays which are absorbed by the ozone layer of our atmosphere.

In this short video (in Italian), you can see how, in China, disinfection using UV rays is already in use. A Chinese company disinfects urban transport buses with UV rays, delivered by columns placed both inside and outside of the vehicle. The disinfection takes a few minutes, as compared with the forty minutes needed by at least two people to disinfect the inside of the bus by hand.

This post is also available in: Italiano


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