Sunlight, heat, and humidity weaken coronavirus – US official
Published Apr 24, 2020 12:00 am
By Reuters and Agence France-Presse
WASHINGTON/PARIS – The coronavirus appears to weaken more quickly when exposed to sunlight, heat and humidity, a US official said on Thursday, a potential sign that the pandemic could become less contagious in summer months.
FILE PHOTO: U.S. President Donald Trump addresses the daily coronavirus task force briefing at the White House in Washington, U.S., April 23, 2020. (REUTERS/Jonathan Ernst/MANILA BULLETIN)
US government researchers have determined that the virus survives best indoors and in dry conditions, and loses potency when temperatures and humidity rise – and especially when it is exposed to sunlight, said William Bryan, acting head of the US Department of Homeland Security's Science and Technology Directorate.
"The virus dies quickest in the presence of direct sunlight," he told a White House news briefing.
The findings could bolster hopes that the coronavirus will mimic the behavior of other respiratory diseases like influenza, which typically are less contagious in warm weather.
But the coronavirus has also proven lethal in warm-weather places like Singapore, raising broader questions about the impact of environmental factors.
President Donald Trump said the findings should be interpreted cautiously, but also claimed vindication for previously suggesting that the coronavirus might recede in summer.
"I once mentioned that maybe it does go away with heat and light. And people didn't like that statement that much," he said at the briefing.
18 hours vs two minutes
On nonporous surfaces like stainless steel, the new coronavirus takes 18 hours to lose half its strength in a dark, low-humidity environment, Bryan said.
In a high-humidity environment, that half-life dropped to six hours, and when the virus was exposed to high humidity and sunlight, the half-life dropped to two minutes, he said.
Researchers found a similar effect with the coronavirus that was suspended in the air - simulating the coughing or sneezing that often spreads the disease. In a dark room, the virus maintained half its strength for an hour. But when exposed to sunlight, it lost half its strength in 90 seconds, Bryan said.
Researchers also found that isopropyl alcohol was a more effective disinfectant than bleach, he said.
Trump said researchers should try to apply their findings to coronavirus patients by inserting light or disinfectant into their bodies.
It has long been known that ultraviolet light has a sterilizing effect, because the radiation damages the virus's genetic material and their ability to replicate.
A key question, however, will be what the intensity and wavelength of the UV light used in the experiment was and whether this accurately mimics natural light conditions in summer.
"It would be good to know how the test was done, and how the results were measured," Benjamin Neuman, chair of biological sciences at Texas A&M University-Texarkana, told AFP.
Bryan concluded that summer-like conditions "will create an environment (where) transmission can be decreased."
He added, though, that reduced spread did not mean the pathogen would be eliminated entirely and social distancing guidelines cannot be fully lifted.
"It would be irresponsible for us to say that we feel that the summer is just going to totally kill the virus and then if it's a freefor-all and that people ignore those guides," he said.
Previous work has also agreed that the virus fares better in cold and dry weather than it does in hot and humid conditions, and the lower rate of spread in southern hemisphere countries where it is early fall and still warm bear this out.
Australia, for example, has had just under 7,000 confirmed cases and 77 deaths -- well below many northern hemisphere nations.
The reasons are thought to include that respiratory droplets remain airborne for longer in colder weather, and that viruses degrade more quickly on hotter surfaces, because a protective layer of fat that envelops them dries out faster.
US health authorities believe that even if COVID-19 cases slow over summer, the rate of infection is likely to increase again in fall and winter, in line with other seasonal viruses like the flu.
FILE PHOTO: U.S. President Donald Trump addresses the daily coronavirus task force briefing at the White House in Washington, U.S., April 23, 2020. (REUTERS/Jonathan Ernst/MANILA BULLETIN)
US government researchers have determined that the virus survives best indoors and in dry conditions, and loses potency when temperatures and humidity rise – and especially when it is exposed to sunlight, said William Bryan, acting head of the US Department of Homeland Security's Science and Technology Directorate.
"The virus dies quickest in the presence of direct sunlight," he told a White House news briefing.
The findings could bolster hopes that the coronavirus will mimic the behavior of other respiratory diseases like influenza, which typically are less contagious in warm weather.
But the coronavirus has also proven lethal in warm-weather places like Singapore, raising broader questions about the impact of environmental factors.
President Donald Trump said the findings should be interpreted cautiously, but also claimed vindication for previously suggesting that the coronavirus might recede in summer.
"I once mentioned that maybe it does go away with heat and light. And people didn't like that statement that much," he said at the briefing.
18 hours vs two minutes
On nonporous surfaces like stainless steel, the new coronavirus takes 18 hours to lose half its strength in a dark, low-humidity environment, Bryan said.
In a high-humidity environment, that half-life dropped to six hours, and when the virus was exposed to high humidity and sunlight, the half-life dropped to two minutes, he said.
Researchers found a similar effect with the coronavirus that was suspended in the air - simulating the coughing or sneezing that often spreads the disease. In a dark room, the virus maintained half its strength for an hour. But when exposed to sunlight, it lost half its strength in 90 seconds, Bryan said.
Researchers also found that isopropyl alcohol was a more effective disinfectant than bleach, he said.
Trump said researchers should try to apply their findings to coronavirus patients by inserting light or disinfectant into their bodies.
It has long been known that ultraviolet light has a sterilizing effect, because the radiation damages the virus's genetic material and their ability to replicate.
A key question, however, will be what the intensity and wavelength of the UV light used in the experiment was and whether this accurately mimics natural light conditions in summer.
"It would be good to know how the test was done, and how the results were measured," Benjamin Neuman, chair of biological sciences at Texas A&M University-Texarkana, told AFP.
Bryan concluded that summer-like conditions "will create an environment (where) transmission can be decreased."
He added, though, that reduced spread did not mean the pathogen would be eliminated entirely and social distancing guidelines cannot be fully lifted.
"It would be irresponsible for us to say that we feel that the summer is just going to totally kill the virus and then if it's a freefor-all and that people ignore those guides," he said.
Previous work has also agreed that the virus fares better in cold and dry weather than it does in hot and humid conditions, and the lower rate of spread in southern hemisphere countries where it is early fall and still warm bear this out.
Australia, for example, has had just under 7,000 confirmed cases and 77 deaths -- well below many northern hemisphere nations.
The reasons are thought to include that respiratory droplets remain airborne for longer in colder weather, and that viruses degrade more quickly on hotter surfaces, because a protective layer of fat that envelops them dries out faster.
US health authorities believe that even if COVID-19 cases slow over summer, the rate of infection is likely to increase again in fall and winter, in line with other seasonal viruses like the flu.