Studies saying warm weather slows COVID-19 not conclusive: Report

The arrival of summer in India may have raised hopes that hot and humid weather could slow the COVID-19 pandemic, however, experts believe that there is not enough proof to conclude any significant vulnerability of the novel coronavirus to seasonal change.

According to a report by the National Academies of Sciences, Engineering, and Medicine, experimental studies do show a relationship between higher temperatures and humidity levels, and reduced survival of SARS-CoV-2, the virus that causes COVID-19, in the laboratory.

However, 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 report said.

The rapid expert consultation report prepared on April 7 aims to provide scientifically grounded principles that are relevant to decision-making about the potential for seasonal variation of SARS-CoV-2.

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 experts said.

However, according to the report, the number of well-controlled studies available at this time on the topic remains small.

There are important conditions regarding the results from experimental studies, it said.

The first concerns the relevance of laboratory conditions to real world conditions, according to the academy.

For example, many of the experimental survival studies have used virus grown in tissue culture media.

The report said that the natural history studies published so far also have conflicting results regarding potential seasonal effects.

They are also hampered by poor data quality, confounding factors, and insufficient time since the beginning of the pandemic from which to draw conclusions, the experts noted.

They explained that there is some evidence to suggest that SARS- CoV-2 may transmit less efficiently in environments with higher ambient temperature and humidity.

"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," the report said.

With experimental studies, environmental conditions can be controlled, but almost always the conditions fail to adequately mimic those of the natural setting, it said.

With natural history studies, the conditions are relevant and reflect the real-world, but there is typically little control of environmental conditions and there are many confounding factors, according to the report.

Because the two approaches are so distinct, it is often difficult to harmonise the findings from the two, and relate the findings from one to the other, it said.