Members of a scientific committee told the White House in a letter Tuesday that while lab-based studies support the claim that the virus that causes the COVID-19 disease is less effective at higher temperatures, “real world” studies are less conclusive, and warm weather might anyway not curb the spread much because so few people are immune.
The National Academy of Sciences (NAS) committee members said in the letter, which was addressed to Dr. Kelvin Droegemeier of the White House Office of Science and Technology Policy, that while controlled experiments showed temperature reduced the viability of the virus, studies done in the natural environment were subject to “significant caveats,” mostly around data quality, and time and location limitations.
The NAS report called for more studies to reach more conclusive results, as well as continued public interventions to curb the spread of the outbreak.
“Although experimental studies show a relationship between higher temperatures and humidity levels, and reduced survival of SARS-CoV-2 in the laboratory, there are many other factors besides environmental temperature, humidity, and survival of the virus outside of the host, that influence and determine transmission rates among humans in the ‘real world,'” the NAS scientists wrote.
“Given the lack of host immunity globally, this reduction in transmission efficiency may not lead to a significant reduction in disease spread without the concomitant adoption of major public health interventions,” they said.
The NAS committee letter suggests this is not an unreasonable claim.
“The laboratory data available so far indicate reduced survival of SARS-CoV-2 at elevated temperatures, and variation in temperature sensitivity as a function of the type of surface on which the virus is placed,” the scientists wrote.
Regarding surface as a factor, a study by the National Institutes of Health showed that the CCP virus survived up to three days on plastic and steel, while on copper, it remained viable for just four hours.
As to “real world” studies on the CCP virus, the scientists said in their letter that “temperature was the variable with the highest relative importance in explaining variations in growth rates although they did see fast growth rates in warmer climates and huge variations in regions with similar climates, suggesting that many factors contribute to transmission.”
The NAS committee members also said that similar viruses to the one that causes COVID-19 have not been seasonal, suggesting less cause for optimism that the CCP virus might be.
“Furthermore, the other coronaviruses causing potentially serious human illness, including both SARS-CoV and MERS-CoV have not demonstrated any evidence of seasonality following their emergence,” they said.
Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center, told CNN: “Although we can hope weather will make some contribution to the reduction in transmission, we can’t rely on it alone. We have to continue to employ social distancing and other measures to reduce transmission.”