“Ninety percent or more of SARS-CoV-2 virus will be inactivated after being exposed for 11-34 minutes of midday sunlight in most US and world cities during summer,” the study published early June in the Photochemistry and Photobiology journal.
The World Health Organization (WHO) defines “viral inactivation” as “a process of enhancing virus safety in which the virus is intentionally ‘killed’.”
The study explains that “Ultraviolet radiation in sunlight is the primary virucidal agent in the environment.” Virucides are substances that destroy viruses.
The researchers question whether the stay-at-home orders, curfews and lockdowns effective in containing the spread of the coronavirus and suggest that there is an environmental element to the spread of COVID-19 aside from direct interaction between people.
“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,” the researchers said.
“In contrast, healthy people outdoors receiving sunlight could have been exposed to lower viral dose with more chances for mounting an efficient immune response,” they added.
The study estimated how long it would take to inactivate the coronavirus in some cities around the world at noon in summer, during maximum solar exposure:
Miami, Florida: 14+ minutes
Houston, Texas: 16+ minutes
Phoenix, Arizona: 18+ minutes
Atlanta, Georgia: 18+ minutes
Los Angeles, California: 18+ minutes
Washington, D.C.: 21+ minutes
Philadelphia, Pennsylvania: 22+ minutes
New York City, New York: 22+ minutes
Chicago, Illinois: 22+ minutes
Boston, Massachusetts: 23+ minutes
Central and South America:
Bogota, Colombia: 11+ minutes
Mexico City, Mexico: 11+ minutes
Sao Paulo, Brazil: 13+ minutes
Buenos Aires, Argentina: 19+ minutes
Barcelona, Spain: 22+ minutes
Paris, France: 28+ minutes
London, UK: 30+ minutes
Moscow, Russia: 34+ minutes
Baghdad, Iraq: 18+ minutes
Tehran, Iran: 19+ minutes
Istanbul, Turkey: 22+ minutes
Kinshasa, Congo: 11+ minutes
Lagos, Nigeria: 11+ minutes
Khartum, Sudan: 11+ minutes
Cairo, Egypt: 16+ minutes
Mumbai, India: 11+ minutes
Shanghai, China: 16+ minutes
Seoul, South Korea: 18+ minutes
Tokyo, Japan: 20+ minutes
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