Hotter summer temperatures are not likely to diminish the spread of the coronavirus, according to new research from the MIT Sloan School of Management

The study’s findings underscore the need to continue social distancing and other measures

Cambridge, Mass., May 7, 2020—Some in the scientific community have expressed optimism that the coronavirus could fade in the summer heat, similar to other viral diseases. Colds and the flu, for instance, typically surge in winter and wane in warmer weather.

But a new study by the MIT Sloan School of Management suggests that summer weather is not likely to have the same effect on the coronavirus, the illness that causes COVID-19. The research, by Hazhir Rahmandad, the Mitsubishi Career Development Professor and an Associate Professor of System Dynamics at the school, finds that while warmer temperatures may offer partial relief to some regions of the world, they will not be enough to curtail the risk of transmission in most places.

“Even though high temperatures and humidity can moderately reduce the ability of the novel coronavirus to survive, the pandemic is not likely to diminish in summer weather,” says Rahmandad.

Prior research on this topic has been inconclusive. Some studies indicate that temperature, humidity, air pressure, ultraviolet light exposure, and rainfall have an impact the spread of COVID-19. These factors potentially change the length of time the virus can live on surfaces and in droplets, moderate the distances the virus may travel through air, and impact individual activities and immune responses. And yet there has been little consensus on the extent of weather’s influence on the virus.

To shed light on these inconsistent findings, Rahmandad and his colleagues, Ran Xu, of the University of Connecticut, Marichi Gupta and Catherine DiGennaro of Massachusetts General Hospital, Navid Ghaffarzadegan of Virginia Tech, and Mohammad S. Jalali of Harvard University Medical School, assembled one of the most comprehensive datasets of the global spread of the COVID-19 pandemic to date.

The dataset includes virus transmission and weather statistics across more than 3,700 locations from December 12, 2019—when the first case of the illness was discovered, to April 22, 2020. They identified key challenges to reliable estimation of weather impacts on transmission, designed a statistical method to overcome these challenges, and validated the method in a simulation study. They then estimated how different weather variables are associated with the reproduction number for COVID-19—meaning its actual ability to spread at a particular time, while controlling for location-specific response trends. Finally, they used the estimates to project the relative weather-related risk of COVID-19 transmission across the world and in large cities.

The research team found a slightly lower transmission risk when temperatures rise above 25°C/77°F. This suggests that many temperate zones with high population density may face larger risks, while some warmer areas of the world may experience slower transmission rates. This finding may partially explain the smaller sizes of outbreaks in southern Asia and Africa.

The study’s results underscore the need to continue social distancing, quarantining, handwashing, and other measures, according to Rahmandad. “Policymakers and the public should remain vigilant in their responses to the health emergency, rather than assuming that the summer climate naturally prevents transmission,” he says. “At best, weather plays only a secondary role in the control of the pandemic.”

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