Could France witness a second COVID-19 wave this summer? For now, this is difficult to work out, since the possible rebound from the pandemic will depend on how the virus responds to summer weather conditions. EURACTIV’s partner Journal de l’environnement reports.
Like influenza, coronaviruses are “weather-sensitive”, which would make them reappear in winter after a summer rest.
In addition to temperature, exposure to UV light, which is more intense in summer, destabilises viral particles. To date, there is no indication of the seasonal behaviour of SARS-CoV-2, an agent of COVID-19.
Similarly, temperate countries in Europe and North America are by far the most affected by the pandemic. By comparison, several countries in tropical Asia, south of China are relatively unaffected as they have a low number of deaths related to COVID-19, such as Thailand (56 deaths) and Vietnam (no deaths), according to official figures.
Africa, a concern
While Africa is the subject of much concern, there are fewer than 2,000 official deaths in Africa to date, mostly in Arab countries and South Africa. However, the WHO estimated on Thursday (7 May) that the disease could infect up to 44 million Africans and kill up to 190,000 in the first year of the pandemic.
Could this mean that the African continent is better protected against the pandemic? And if so, is this a consequence of the weather-sensitivity of the virus?
Not necessarily: Africa has a much lower population density than Europe or Asia, and the youngest population in the world. Although it has several megacities, including Lagos in Nigeria, air traffic with other world capitals is reduced, limiting the introduction of the virus. Several African countries, which were affected recently, were able to adopt social distancing and containment measures quickly.
A scientific debate that is not clear-cut
The weather-sensitivity of SARS-CoV-2 is still a matter of debate among scientists. According to a study published in the Canadian Medical Association Journal (CMAJ) on Friday (8 May), temperature and latitude do not affect the increase in the number of cases. Peter Jüni of the Institute for Health Policy at the University of Toronto and his colleagues based their findings on over 375,000 cases in 144 countries and US states.
By contrast, humidity seems to have a slightly positive effect. When humidity increases by 10%, the transmission rate decreases by 9%. This could support the hypothesis, unproven to date, put forward at the end of March by the Italian Society of Environmental Medicine (SIMA).
According to the Italian experts, fine particles could carry the virus, thus promoting its spread. Moisture, which reduces the level of fine particles, could, on the other hand, slow it down.
In contrast to the Canadian researchers, a Brazilian team supports the idea that the virus is sensitive to temperature. Published at the end of April in the Science of Total Environment, their study shows that, in Brazil, any 1°C increase reduces the number of new cases by 5%.
Once temperatures hit 25.8°C, the authors of the study observed a plateau effect, with transmission remaining, but at a low level.
(Edited by Samuel Stolton)