Does the summer sun have an effect on the coronavirus? – Checked

January 02, 2022 08:00 am | Reading time: 3 minutes
January 02, 2022 08:00 am
| Reading time: 3 minutes

If you only have a few seconds, read these lines:

  • The so-called germicidal radiation does not reach the surface of the planet. But UVB wavelengths do cause a small viral inactivation.
  • The sun could play a role in contagion at a distance but not at close range. On the other hand, there is a lack of evidence to be able to establish a real relationship between infections and the time of year.
  • Specialists assure that adequate ventilation is key to reducing the risk of transmission of the coronavirus.

After going through almost a second year of the pandemic, we are back in summer. Holidays and rest are in the air and the desire to enjoy the good weather appears: swimming pool, park, sea, mountain, squares, they are all welcome. In addition to recreating ourselves, we feel that with the sun and heat we are safe from SARS-CoV-2, the virus that causes COVID-19. But unfortunately, the coronavirus continues to accompany us and we cannot neglect ourselves neither in the sun nor in the shade, literally.

Thus the question arises, does the summer sun have an effect on the coronavirus? Are there fewer infections during the summer? Scientists deny that solar radiation serves to inactivate the virus long enough to prevent person-to-person transmission. We review what evidence emerged in this last year in this regard.

Solar radiation

The use of radiation to disinfect surfaces is not new. In fact, its discovery earned the Danish physician Niels Finsen the Nobel Prize in 1903. “Germicidal” radiation, so called because it destroys bacteria and other harmful germs, comes from artificial lamps that use a limited wavelength: UVC rays. , a type of high-energy ultraviolet radiation, in the range of 100 to 280 nanometers (nm).

In the scientific literature you can find several studies who use this tool successfully to reduce the burden of SARS-CoV-2 on medical equipment, work surfaces and health facilities.

This may lead to the belief that the strong summer sun could fulfill the same function. But it’s not like that. “Germicidal radiation does not reach the earth’s surface, because it is filtered by gases from the atmosphere. If this were not the case, we would all have skin cancer, cataracts or other diseases, since it is very harmful “, he told Checked Beatriz Toselli, doctor in Chemistry specialized in chemical and radiative processes in the atmosphere at the National University of Córdoba.

However, there is a lesser potential viral inactivation attributable to UVB wavelengths from the sun (range 290 to 315 nm) that do reach the surface. “A small fraction of UVB radiation reaches the earth, but it has a direct impact on everything that absorbs it: for example, on the structure of the virus “, explained to this medium the specialist in photobiology and photochemistry Franco Cabrerizo, a researcher at Conicet at the Technological Institute of Chascomús, which also depends on the National University of San Martín.

A seasonal illness?

In a job Published in Nature Scientific Reports, a group of Italian researchers studied the relationship between solar radiation throughout the planet during the pandemic and mortality from COVID-19. According to their data, the Radiation that reaches the temperate regions of the Earth at noon during summers is enough to inactivate 63% of the virus in aerosols in open space in about 2 minutes.

For its part, American researchers found a similar trend but with slightly longer times: a 90% inactivation of the virus after being exposed between 11 and 34 minutes (depending on the latitude) to the noonday sun. Conversely, the virus would remain infective for longer in winter.

This could make us think of a seasonality of the disease. But there is still a lack of evidence to be able to establish a real relationship between infections and the time of year. “Humidity and temperature have some role in the potential seasonality of the virus, but it is something very complex to study. At the moment, counterexamples of contagion waves abound in summer in numerous regions.s. And this theory is much more difficult to verify in regions without climatic seasonality, ”commented virologist Humberto Debat, a researcher at INTA in Córdoba.

The importance of ventilation

In conclusion, the sun does not reduce the risk of person-to-person contagion in close proximity. “The decay of the effectiveness of the virus in aerosols is a slow process compared to its rapid dispersal. The sun may play a role in distant contagion (when the aerosols have been in the air for a while) but not in close proximity, where the highest concentration is in the air just exhaled by the person ”, he explained to Checked Andrea Pineda Rojas, PhD in Atmospheric Sciences and Conicet researcher at the Center for Research on the Sea and Atmosphere (CIMA / UBA-Conicet)

It is clear that there is an important difference between the virus being inactivated by radiation on surfaces under certain conditions and assuming that the sun prevents the transmission of the coronavirus.

Given that the main route of infection is person to person, the recommendations to protect yourself are still mainly: distancing, correct use of face masks, frequent hand washing and ventilation of the rooms.

Ventilation is very important. The aerosol resulting from a continuous talk of 1 hour in a poorly ventilated environment gives a risk of infection of between 10 and 20%, this risk is reduced at least 3 times if the ventilated air is replaced “, concluded Juan Gabriel Yañuk, doctor in molecular biology and researcher at the National University of San Martín.

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Does the summer sun have an effect on the coronavirus? – Checked