Even if the cold spell expected in the coming days will put a short break, the spring season marks the arrival of pollen. In addition to allergies, their multiplication in the air would increase the risk of Covid-19 infection.
- Spring marks the return of airborne pollen
- A priori pollen cannot transmit viral particles
- On the other hand, it can have effects on the functioning of the immune system
The more pollen there is, the higher the risk of being infected with Covid-19. It is the affirmation of a study published in the journal PNAS. The authors believe that the multiplication of pollen in the air would increase the chances of being contaminated by the coronavirus. To achieve this result, they analyzed several data collected between January 1 and April 8, 2020 in 31 countries around the world. This information concerned the rate of infection with SARS-CoV-2, the level of pollen, temperatures, humidity in the air, population density as well as the restriction measures put in place.
The immune system is weaker in contact with pollens
The scientists started from the observation that exposure to pollen weakens the immunity of individuals against certain seasonal respiratory viruses. Indeed, when such a pathogen enters the body, interferons – proteins naturally produced by the immune system – signal it to cells that produce antibodies. But when the virus is inhaled with air concentrated in pollen, the production of interferons is slowed down. Thus, the body’s antiviral response is less strong and the individual falls ill more easily. With their study, they therefore wanted to determine whether this phenomenon also applied to Covid-19.
Pollens explain 44% of the variability in the infection rate
According to their observations, the amount of pollen suspended in the air, sometimes linked to other factors such as humidity or temperature, explained on average 44% of the variability in infection rates. On the other hand, these also increased more when the pollen concentrations were higher during the previous four days. For example, in a German city, if it was 500 pollen grains per m3 per day, infection rates would worsen by more than 20%. The researchers thus estimate that without the containment measures – which they consider effective – this rate could have been 4% per 100 pollen grains per m3.
Even outside, respect barrier gestures
The health measures taken by the government this Thursday, April 1 rely on the fact that the contagion is stronger inside than outside. It is for this reason that all French people, regardless of the department, can stay outside as long as they wish. Previously, the limit was set at one hour of daily walks. But, even outside, we must continue to respect barrier gestures – regular hand washing, social distancing, etc. – to limit the risk of contagion.
So far, no study proves that pollen can contain and transmit viral particles. You should therefore not be afraid of pollen as such because it is the combination of its high quantity in the air and contact with the virus that increases the risk of being infected. Nevertheless, scientists advise people with comorbidities to wear a filter mask when there is a lot of pollen in the air.
Pollen levels will increase
With the onset of spring, pollen levels will increase. In France, several departments already have an average risk of allergies. And only one, the Var, is classified in the high category according to the National Aerobiological Surveillance Network (RNSA). In addition to these allergies, the concentration of pollen in the air could therefore also impact the coronavirus epidemic, by aggravating the risk of being infected. Currently, more than four million people have Covid-19 in France.
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