Is the SARS-CoV-2 coronavirus resistant to sunlight?
Text updated on 2020-06-22
On clear days, sunlight inactivates the SARS-CoV-2 coronavirus suspended in saliva within 7 minutes, which dries on smooth material. For non-porous contaminated materials, one hour in the sun in the middle of summer should be sufficient to disinfect!
The sun can have several effects on objects: it sends out ultraviolet (UV) rays, it heats objects, and it dries them out. To understand the effect of the sun on the stability of the SARS-CoV-2 coronavirus, it is therefore necessary to examine the effect of UV, heat and drying on SARS-CoV-2.
A recent study shows that simulated sunlight inactivates within minutes the SARS-CoV-2 coronavirus that was suspended in saliva and dried on stainless steel. The illumination used to simulate the sun represents light at a latitude of 40°N at sea level on clear days.
Under these conditions, 90% of the infectious virus is inactivated after 7 minutes in saliva with illumination corresponding to the summer solstice and after 14 minutes for the winter solstice. Lower illuminations corresponding to cloudy weather also eliminate the virus, but more slowly.
The solution in which the virus is suspended has a strong impact on the inactivation rate of the coronavirus, suggesting that the inactivation time may vary depending on the content of saliva, or whether the virus comes from mucus, nose, tears, or feces.
These data indicate that a one-hour exposure to sunlight in midsummer can be effective as a disinfectant to decontaminate non-porous materials such as steel. These observations also suggest that the spread of the virus may be slowed during the summer due to the greater strength of sunlight combined with the fact that interpersonal interactions take place more often outdoors.
A study shows that simulated sunlight rapidly inactivates the SARS-CoV-2 coronavirus suspended in saliva or culture media and then dried on stainless steel. When exposed to type B UV corresponding to sunlight at a latitude of 40°N at sea level on clear days, 90% of the infectious virus was inactivated after 7 minutes in saliva during the summer solstice and after 14 minutes during the winter solstice. These data indicate that natural sunlight can be effective as a disinfectant for contaminated non-porous materials.Ratnesar-Shumate, S., Williams, G., Green, B., Krause, M., Holland, B., Wood, S., .... Dabisch, P. (2020). Simulated Sunlight Rapidly Inactivates SARS-CoV-2 on Surfaces. The Journal of Infectious Diseases.
A study indicating the spectrum of sunlight when it arrives on Earth. UV-A and UV-C do not reach the Earth and are filtered out by the ozone layer. Only UV-A and UV-B rays reach the Earth.Moan, J. (2001). 7 Visible Light and UV Radiation. Radiation at Home, Outdoors and in the Work-Place.
The stability of the SARS-CoV-2 coronavirus depends on temperature and humidity. Heat effectively inactivates SARS-CoV-2. At 70 degrees, the SARS-CoV-2 coronavirus is inactivated within 5 minutes. Moisture also affects the virus, which is more resistant if it is kept cold and dry.Chin, A., Chu, J., Perera, M., Hui, K., Yen, H. L., Chan, M., ... & Poon, L. (2020). Stability of SARS-CoV-2 in different environmental conditions. The Lancet Microbe.
A UV-C treatment at 260 nm (filtered by the ozone layer and thus not reaching the earth) of a liquid solution containing SARS-CoV-1, the SARS agent, which is very similar in structure to the coronavirus SARS-CoV-2, makes it possible to inactivate 75% of the pathogenic effects in cell culture in 15 minutes and 100% of the effects in 60 minutes.Duan, S. M., Zhao, X. S., Wen, R. F., Huang, J. J., Pi, G. H., Zhang, S. X., ... & Dong, X. P. (2003). Stability of SARS coronavirus in human specimens and environment and its sensitivity to heating and UV irradiation. Biomedical and environmental sciences: BES, 16(3), 246-255.