Back in early March Trump speculated that “The virus that we’re talking about … a lot of people think that goes away in April, with the heat”. While overly optimistic, this prediction may turn out to be partly right. We now have some early research showing that COVID-19 may be less contagious in warmer weather.
A new draft of a paper written by Wang et al. was released April 3rd, showing that higher temperature and higher humidity lead to lower COVID-19 transmission. Published in SSRN, this paper analyzes cities across China, and compared the spread of COVID-19 to weather data. It was found that areas with higher temperatures and higher humidity had fewer cases of COVID-19. The virus was still quite contagious throughout the country, warmer southern regions seemed to be moderately protected.
This paper does not look at “why” COVID-19 spreads less in warm weather, but it is believed to follow a similar mechanism that is seen in other viruses. Viral particles are more stable at lower temperatures, and prefer the low humidity seen in cooler weather. There is also evidence that people have a weakened immune system in cold weather. Unfortunately, the topic is not fully understood at this time, but it is clear that many viruses spread more readily in cold weather.
It should be noted that this paper is working with data from China. There are serious concerns that the statistics coming from China are untrustworthy. At the time the original draft of this paper was submitted there were still less than 100,000 cases outside of China, meaning there was insufficient data to include regions outside of China in the study. Hopefully, academics follow up on this research as more data becomes available.
While warmer weather is not a substitute for social distancing, this study gives reason to be cautiously optimistic. The authors predict that the transmissibility will drop substantially in North America and Europe as the weather warms in the summer. Trump’s prediction that the pandemic will end in April seems doomed, but there is a good chance that the worst of the disease will have passed by summer.
This is part of a series on preliminary research that relate to the COVID-19 pandemic. As this covers papers that are not finalized in an area of study that is evolving rapidly, it is possible that some of this research will end up being modified, and should be taken as such. Other articles in this series cover hydroxychloroquine, the use of masks and airborne transmission.
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