More corona if there is more pollen in the air

The more pollen grains there are in the air, the more people become infected with the corona virus. Which writes a large international team this week in the magazine PNAS. It is a correlation, and not necessarily cause and effect. But such a causal relationship has been demonstrated for other respiratory viruses. It is also known that exposure to pollen reduces the resistance to viruses in our respiratory tract.

The study includes data from 130 pollen monitoring stations in 31 countries, combined with corona contamination figures in those countries. Worldwide, it was seen that the contamination figures increase with an increasing pollen concentration, with a delay of 4 to 5 days. That is exactly the incubation period of the virus. For every 100 pollen grains per cubic meter of air, the contamination figures increase by an average of 4 percent. “This effect can potentially contribute 10 to 30 percent of the contamination rates,” the article said PNAS.

Interestingly enough, this applies to the entire population – not just hay fever patients. These are not registered in corona research.

Recent German research has shown that exposure to pollen increases our susceptibility to certain viruses. As soon as pollen grains make contact with the mucous membranes, the production of antiviral substances in them decreases: interferons. The result is an increased susceptibility to respiratory viruses. Perhaps, the researchers now register PNAS, it also applies to SARS-CoV-2.

Air past a spinning roller

Three Dutch institutes took part in the study: the Leiden LUMC, the Elkerliek Hospital in Helmond and Wageningen UR. They helped register the amount of pollen in the air. “It is the same everywhere,” says Letty de Weger of the LUMC. “Our measuring station is on the roof of the LUMC. It is a kind of vacuum cleaner that sucks in air and lets it flow along a rotating roller that has been smeared with a kind of petroleum jelly. Solid particles stick to it, including pollen. ”

The station runs seven days a week. De Weger and her colleagues analyze the yield at set times. “The pollen season has already started,” she says. “At the end of February, we measured a peak of about 1,400 pollen grains per cubic meter of air.” This could theoretically lead to a significant increase in the number of infections. “But it is difficult to say something about that in concrete terms,” ​​adds De Weger. “There are many factors that influence the contamination figures. In addition to human factors, all kinds of environmental factors, such as temperature and humidity. ”

How did the researchers filter out the effect of pollen? “Colleagues from Germany, Finland, Hungary and the US have taken care of that part,” De Weger replies. “They used advanced statistical analysis methods to unravel which factors do or do not individually correlate with the increase in the number of corona infections.”

More testing

Isn’t the higher number of corona infections following days with a lot of pollen simply explained by the fact that more people then get tested? De Weger does not think so. “This year you did indeed see more tests on days with a lot of pollen,” she says, “but the percentage of infections was actually lower.”

The PNAS authors want to continue the research over a longer period of time this year. Experimental research into the effect of pollen on our defense against corona is also planned. “The effect of other factors, such as air pollution, should also be investigated,” they write.

The researchers recommend that high-risk groups wear a high-quality mouth mask during the pollen season.

Correction (9 March 2021): An earlier version of this article stated that the Elkerliek Hospital is located in Heerlen. That is incorrect and adjusted.
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