They say pollen could be a culprit in respiratory infections, not because the viruses hitch a ride on pollen grains and travel into our mouth, eyes, and nose, but because pollen seems to perturb our immune defenses, even if a person isn’t allergic to it.
“When we inhale pollen, they end up on our nasal mucosa and here, they diminish the expression of genes that are important for the defense against airborne viruses,” study author Stefanie Gilles, PhD, chair of environmental medicine at the Technical University of Munich in Germany, said in a press conference.
In a study published last year, Gilles found that mice exposed to pollen made less interferon and other protective chemical signals to the immune system. Those then infected with a respiratory virus had more virus in their bodies compared with mice not exposed to pollen. She seemed to see the same effect in human volunteers.
The study authors think pollen may cause the body to drop its defenses against the airborne virus that causes COVID-19, too.
“If you’re in a crowded room and other people are there that are asymptomatic, and you’ve just been breathing in pollen all day long, chances are that you’re going to be more susceptible to the virus,” says Lewis Ziska, PhD, a plant physiologist who studies pollen, climate change, and health at Columbia University’s Mailman School of Public Health in New York City. “Having a mask is obviously really critical in that regard.”
Masks do a great job of blocking pollen, so wearing one is even more important when pollen and viruses are floating around, he says.
Other researchers, however, say that, while the study raises some interesting questions, it can’t prove that pollen is increasing COVID-19 infections.
“Just because two things happen at the same time doesn’t mean that one causes the other,” says Martijn Hoogeveen, PhD, a professor of technical sciences and environment at The Open University in the Netherlands.
Hoogeveen’s recent study, published in Science of the Total Environment, found that the arrival of pollen season in the Netherlands coincides with the end of flu season, and that COVID-19 infection peaks tend to follow a similar pattern — exactly the opposite of the PNAS study.
Another preprint study, which focused on the Chicago area, found the same thing — as pollen climbs, flu cases drop. The researchers behind that study think pollen may actually compete with viruses in our airways, helping to block them from infecting our cells.