Press release 9.3.2021

Higher airborne pollen concentrations correlate with increased COVID-19 infection rates

A recent international study showed that higher pollen concentrations in the air correlate with increased COVID-19 infection rates. Pollen exposure weakens the response of immune system to some seasonal respiratory viruses. The effect was not connected with pollen allergy, but exposure to pollen can in itself weaken the capability of the body to fight off viruses.
Birch pollen particles seen through a microscope. Photo: Pollen forecasting of the University of Turku.

Various factors explain the variation in COVID-19 infection rates. The study reports that airborne pollen, sometimes in synergy with humidity and temperature, explained on average over 40% of the increase in the SARS-CoV-2 infection rate. The effect of high airborne pollen concentrations was not immediate. In most cases, infection rates increased 4 days after the peak in pollen concentrations. That corresponds roughly to the COVID-19 incubation period.

Microbiological laboratory experiments reported in preceding publications showed that pollen itself impacts the antiviral defense of the respiratory epithelium, where the viruses attack. Pollen exposure diminishes the release of antiviral interferon. These interferons help the immune system fight the viruses. Thus, exposure to pollen can diminish the immunity against viruses.

The study also estimated effects of different lockdown measures in the spring of 2020. Without lockdown measures, high airborne pollen abundance can lead to a noticeable increase of infection rates – up to tens of percent. Lockdown measures halved the infection rates under similar pollen concentrations. During a lockdown people have less exposure to both the virus and the pollen that diminishes the immune response.

Timely information helps in reducing exposure to pollen

“Attention should be paid to timely information on the forthcoming pollen season and days with particularly high pollen concentrations. As a practical measure, it is recommended to reduce the pollen exposure during high pollen season. Pollen exposure can be avoided by reducing the time spent outdoors during the peak pollen season or using pollen particle filtering masks outdoors”, says Professor Mikhail Sofiev from the Finnish Meteorological Institute, who participated in the data analysis of the study.

“The pollen season is about to begin, and the up-to-date information on pollen concentrations in the air can be found on Norkko service, a website maintained by the Pollen Forecasting of the University of Turku. Our researchers monitor pollen concentrations in the air year-round, so as soon as the first pollen particles are detected in the air, we're able to update the information to Norkko”, says Adjunct Professor Annika Saarto from the University of Turku.

From Finland, Finnish Meteorological Institute (FMI) and University of Turku (UTU) participated in the study. The study is published in highly-rated Proceedings of the US National Academy of Sciences (PNAS) journal in March 2021. The study used data from 31 countries and around 150 scientists all around the world participated in the work. In the research, the FMI researchers worked in the core group as data analysts and participated in the design of the analysis, and the UTU provided the pollen data for Finland.

FMI, in collaboration with UTU and other institutes in Finland and worldwide, actively develops pollen modelling and monitoring technologies, recently expanding the research to other biological particles in the air: spores, viruses, bacteria, etc. The FMI atmospheric composition model SILAM incorporates the most advanced pollen system in the world.

Pollen forecasting of University of Turku has monitored pollen concentrations in the air in Finland and published pollen forecasts since the 1970s. Norkko service uses Smart-Pollen technology, the most advanced pollen system in the world, produced in collaboration with the Finnish Meteorological Institute. The researchers at Pollen forecasting of the University of Turku widely participate in research about pollen and spores in the air. Valuable long-term pollen data covering several decades enables, for example, detecting and studying the impacts of climate change.

More information:

Research Professor Mikhail Sofiev, Atmospheric Composition Department of Finnish Meteorological Institute,, tel. +358 50 3290578 (pollen modelling and forecasting, data analysis, atmospheric physics and chemistry, atmospheric composition modelling)

Adjunct Professor Annika Saarto, Pollen forecasting of the University of Turku,, tel. +358 50 344 5531 (aerobiology, pollen observations, Finnish pollen information and forecasting service)

Finnish Meteorological Institute pollen forecasts for Europe and Northern Europe

University of Turku pollen information service for Finland

Copernicus Atmospheric Monitoring Service CAMS, air quality and pollen forecasts

Research article: “Higher airborne pollen concentrations correlated with increased SARS-CoV-2 infection rates, as evidenced from 31 countries across the globe”,

ResearchScience newsPollenCOVID-19