SARS-CoV-2 would circulate more when temperatures are low and the air humid. This suggests that Covid-19 is, like the flu, a seasonal infection.
- Global analysis of the relationship between the rate of transmission (R0) of Covid-19 and temperature and humidity shows that the virus adopts a seasonal character.
- However, this does not exclude an increase in contamination when temperatures are high, as was the case this summer worldwide.
Is Covid-19 in the process of being classified as a seasonal disease? While the first wave of the pandemic occurred in the spring of 2020, when temperatures were still cool, and subsequent waves of the disease occurred in the fall and winter, a key question regarding SARS-CoV -2 is whether it behaves, or will behave, like a seasonal virus like the flu, or if it will be transmitted the same way at any time of the year.
A new study conducted by the Barcelona Institute for Global Health (ISGlobal) and published in Nature Computational Science provides strong evidence that Covid-19 is a seasonal infection linked to low temperatures and humidity, much like seasonal flu.
A disease that thrives in winter conditions
To determine whether Covid-19 is a seasonal disease, researchers first analyzed the association of temperature and humidity in the initial phase of the spread of SARS-CoV-2 in 162 countries on five continents. , before changes in human behavior and public health policies were put in place. The results show a negative relationship between the rate of transmission (R0) and temperature and humidity on a global scale. This means that higher transmission rates were associated with lower temperatures and humidity.
The team then analyzed how this association between climate and disease changed over time, and whether it was consistent at different geographic scales. To do this, they developed a statistical method that identifies similar patterns of variation at different points in time. Once again, a correlation between the number of cases of the disease and the cold and humid climate was found, with consistent patterns during the first, second and third waves of the pandemic at different spatial scales: at the global level, at the level of the countries, at the level of individual regions in heavily affected countries (Lombardy, Thuringia and Catalonia) and even at the level of cities (Barcelona).
A rise in cases during the summer remains possible
If Covid-19 is indeed a seasonal disease, how can we explain that the pattern favored by researchers was broken during the summer on all continents. ? “This could be explained by several factors, including the massive gatherings of young people, tourism and air conditioning, among others”explains Alejandro Fontal, researcher at ISGlobal and first author of the study.
The research team has also established an epidemiological model that shows that integrating temperature into the transmission rate can better predict the rise and fall of different waves, including the first and third in Europe. “Overall, our results confirm that Covid-19 is a true low-temperature seasonal infection, similar to influenza and milder circulating coronaviruses.emphasizes Xavier Rodó, who coordinated the study. This link justifies emphasizing air hygiene by improving indoor ventilation, as aerosols are able to remain airborne longer.”
The government remains “vigilant” in the face of Covid-19
The publication of this study comes as the Minister of Health, Olivier Véran, acknowledged on BFMTV and RMC “a small surge of Covid… but without there being an increase in hospitalizations as last fall” . But autumn leads to an increase in the circulation of respiratory viruses… and in particular that of the flu for which the vaccination campaign against the seasonal flu begins this Friday, October 22 in France. The Minister warned of a virus particularly “strong” this year, and indicated that 10 million doses are already available in pharmacies, i.e. 20% more than in 2020, “so that everyone can be vaccinated”.
The Minister of Health also recalled that a further increase in SARS-CoV-2 contamination was not excluded in the weeks to come. “Everything is possible”he said, even if he rules out a strong resumption of the epidemic for the moment. “I don’t think that’s the most likely scenario. But we remain extremely vigilant.” He stressed the importance of maintaining barrier gestures and respecting the health pass to guard against the increase in Covid-19 cases. “The time has probably not come to give the feeling that the virus would not be a danger for us […] and remove tools that protect us.”
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