The coronavirus is unlikely to go away once the weather warms up, according to experts from the National Academies of Sciences (NAS).
“There is some evidence to suggest that SARS-CoV-2 (the virus that causes COVID-19) may transmit less efficiently in environments with higher ambient temperature and humidity; however, given the lack of host immunity globally, this reduction in transmission efficiency may not lead to a significant reduction in disease spread" without the adoption of major public health interventions, the NAS stated in a letter to the White House.
"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,” says the letter addressed to Dr Kelvin Droegemeier, head of the White House’s Office of Science and Technology Policy.
The assessment was done by members of the National Academies' standing committee on emerging infectious diseases and 21st century health threats. The NAS letter serves as a warning to the White House not to count on a summer respite and perhaps prepare for a second wave of the virus once the first surge in cases is over.
Last month, the World Health Organization (WHO) had also said that COVID-19 can be transmitted in all areas, including hot and humid weather. "From the evidence so far, the COVID-19 virus can be transmitted in all areas, including areas with hot and humid weather. Regardless of climate, adopt protective measures if you live in, or travel to an area reporting COVID-19," the WHO said.
The NAS experts say that studies published so far have conflicting results regarding potential seasonal effects. The results are hampered by poor data quality, confounding factors associated with geography, access to public health and healthcare systems, per capita income, human behaviorial patterns, availability of diagnostics, and insufficient time since the beginning of the pandemic from which to draw conclusions.
According to the scientists, some limited data support a potential waning of cases in warmer and more humid seasons, "yet none are without major limitations".
"Given that countries currently in ‘summer’ climates, such as Australia and Iran, are experiencing rapid virus spread, a decrease in cases with increases in humidity and temperature elsewhere should not be assumed. Given the lack of immunity to SARS-CoV-2 across the world, if there is an effect of temperature and humidity on transmission, it may not be as apparent as with other respiratory viruses for which there is at least some pre-existing immunity," they write.
The experts say that it may be useful to note that pandemic influenza strains have not shown the typical seasonal pattern of endemic or epidemic strains. "There have been 10 influenza pandemics in the past 250-plus years. Two started in the northern hemisphere winter, three in spring, two in summer, and three in the fall. All had a peak second wave approximately six months after the emergence of the virus in the human population, regardless of when the initial introduction occurred," say researchers.
The scientists have called for additional studies as the COVID-19 pandemic unfolds, which could shed light on the effects of climate on transmission.
"In summary, though 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’," they conclude.
Globally, over 1,484,811 cases have been reported as of April 9, and more than 88,538 have died in the coronavirus pandemic, shows the John Hopkins tracker. In the US, more than 432,132 cases have been reported and at least 14,817 have died.