Does climate influence the spread of the Coronavirus?

Some studies have converged on the hypothesis that Covid-19 spreads more with a cool and dry climate than with a hot and humid climate. The same phenomenon was observed for the SARS virus.

The most recent analysis carried out by the Boston MIT on data collected by Johns Hopkins University in Baltimore, shows that the maximum number of Coronavirus cases occurred in all those areas with temperatures between 3 and 13° C.

In contrast, countries with average temperatures above 18° C have seen less than 5 percent of the total cases. The example is clear in the United States, where the southern countries (Texas, Florida and Arizona) have so far recorded a slower growth rate than the northern states (such as Washington, New York and Colorado).

The data which has emerged in two other studies also seem convincing: In the first, 95 percent of the positive cases globally occurred with temperatures ranging from -2 to 10 degrees in dry conditions. The second, published by a team led by researchers from the University of Beihang, China, examined the situation in Chinese cities and found that, in the early days of the epidemic, in January, before any government intervention, warm and wet cities saw a slower diffusion rate than the cold and dry ones.

Other researchers have underlined how, between 11 and 19 March, there has been an increase of about ten thousand infections in regions with temperatures below 18 degrees.

However, caution should be exercised and this data should not be taken as solid, also because there is no objective scientific evidence for the moment. The correlation between diffusion and climatic conditions could be linked to other reasons such as government decisions, lines of contagion or the lack of tests to be submitted to the population.

Marc Lipsitch, director of the Center for Communicable Disease Dynamics at the Harvard School of Public Health, denied the link: “Although we can expect modest decreases in Covid-19’s infectiousness in warmer and wetter climatic conditions, it is not reasonable to expect that these decreases alone will slow down the transmission enough to create a lower curve.”

The only measures aimed at combating the pandemic which seem to be working, are those of isolation and social distancing, in addition to the almost total closure of production activities.

Other observations by climatologists do not support the notion of a link between climate and the spread of the virus, such as the study by the Bicocca Universities of Milan, Roma Tre, Chieti-Pescara, which compared the climatic data of the province of Wuhan and of Lombardy and Veneto from 20 February to 18 March.

The results detected by ten representative stations were taken into consideration, both of the three main outbreaks of the virus (Codogno, Nembro and Vo ‘Euganeo areas) and of the other most affected provinces of Lombardy (Bergamo, Brescia, Cremona, Pavia). And there were no correlations between the number of infections and the weather.

Thus, the hope that Covid-19 would behave like SARS in July 2003, is not realistic.

Another unknown is that of the correlation between smog and Coronavirus: a hypothesis raised after a study conducted by the Italian Society of Environmental Medicine (Sima) together with the Universities of Bologna and Bari, showing a link between the high levels of pollution and the outbreak of Covid-19 in the Po Valley.

But researcher Federico Fierli warned that the interactions and mechanisms that govern the epidemiology and the spread of a virus “are too complex to establish a direct relationship on the database for now very limited”.