- Anne Hidalgo assured on May 10 that "particle pollution leads to an accelerated spread of the coronavirus".
- Some work has been published on the issue, but it is still too early to draw conclusions.
- The health risks of exposure to fine particles and nitrogen dioxide are, however, well documented.
Does pollution play a role in the spread of Covid-19? Anne Hidalgo is convinced of this. "Studies have shown that particle pollution leads to an accelerated spread of the coronavirus," said the mayor of Paris on May 10 in an interview with the Journal du dimanche . A strategic declaration, while the Paris city hall is reorganizing traffic routes in the capital to avoid a massive return of vehicles and associated emissions.
20 Minutes deciphers this statement from the mayor of Paris.
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- Are there any studies on this?
Three publications from different universities have recently investigated whether exposure to air pollution increases the number of deaths associated with Covid-19.
At the end of March, a note published by Italian researchers studied the level of pollution and the number of cases of Covid-19. We returned to this note in more detail at the time of its publication.
In April, it is Harvard University's turn to look into this theme. According to its authors, an increase of one microgram of PM 2.5 suspended particles is "associated with an 8% increase in the death rate linked to Covid-19". The researchers drew on data recorded in 3,000 American counties, representing 98% of the pollution. They adjusted the results by taking into account several factors such as the size or density of the population, the number of people tested, or obesity and smoking. They thus respond to one of the main criticisms addressed to the Italian note, which had not taken into account the density of the population of the regions studied.
A third publication looked at a possible link between air pollution and mortality from Covid-19. On April 20, Yaron Ogen, a researcher at Martin Luther Halle-Wittenberg University, published a study in the journal Science of Total Environment . Yaron Ogen took into account three factors: the number of deaths in 66 regions of Italy, Spain, France and Germany, nitrogen dioxide pollution and the air flows recorded in these regions.
"The results show that of the 4,443 deaths, 3,487 (78%) occurred in five regions located in northern Italy and central Spain," writes the scientist. In addition, these same five regions have the highest concentrations of NO2 [nitrogen dioxide] combined with a downward flow of air which prevents effective dispersion of air pollution. These results indicate that long-term exposure to this pollutant may be one of the most significant contributors to mortality from the Covid-19 virus in these regions and possibly worldwide. "
- Are these studies reliable?
These publications suffer from shortcomings: the Italian publication "is not at all a scientific article, it is a note, reminds Cathy Clerbaux, research director at CNRS at 20 Minutes . It is absolutely false to say that this is a very serious study, as long as a study is not validated by peers. The Harvard publication has also not been peer-reviewed.
Yaron Ogen also warned against any hasty reading of his work: "The correlation found does not necessarily mean a causal link," he stressed to France 24.
- Are there health risks linked to pollution?
The risks of exposure to fine particles and nitrogen dioxide are well documented. "Fine particles and nitrogen dioxide significantly increase the risk of respiratory diseases, but they will especially have an impact on cardiovascular diseases", recalls to 20 Minutes Thomas Bourdrel, doctor and founder of the Air Santé Climat collective. These pathologies linked to air pollution "are part of the co-morbidity factors of Covid-19", underlines the doctor, who highlights a scientific article published in 2007. According to this article, exposure to air pollutants can modify "host immunity to respiratory viral infections".
- Does pollution promote the spread of the virus?
"It is almost certain that the virus is transported by fine particles," says Thomas Bourdrel. However, "once we have said that, we do not say anything, because we do not know if it is infectious [during this transport]. It is also unclear how far he could travel.
For him, the question does not arise for outdoor spaces, because "we will never find a concentration of virus such that it is contaminating". For confined spaces, the High Council for Public Health had explained on April 7 "that aerosol transmission [by air] cannot be excluded", and that this risk occurs mainly in the services of hospitals receiving Covid patients.
WHO is cautious about a possible aerosol transmission: it explains that this can be possible when certain treatments, such as intubation, are given to a patient, but declares itself to be much more reserved for other situations. The more dense droplets remain the main mode of transmission of the disease in the current state of knowledge.
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