With increased pollen levels in the air, higher rates of SARS-CoV-2 infections can be observed. This is the conclusion of a large-scale study conducted by an international team of researchers from the Technische Universität München and the Helmholtz Zentrum München. Individuals in high-risk groups could protect themselves by observing pollen forecasts and wearing masks with dust filters.
Last year's outbreak of the COVID-19 pandemic in the northern hemisphere coincided in time with the richest time of year for airborne pollen. These observations prompted an international team of researchers to conduct a thorough investigation. The scientists wanted to know whether there is a demonstrable link between airborne pollen concentrations and SARS-CoV-2 infection rates.
The researchers collected data on airborne pollen concentrations, weather conditions and SARS-CoV-2 infections - taking into account the daily variation in infection rates and the total number of positive tests. In their calculations, the researchers also included data on population density and the effects of containment measures. The data covered 31 countries on five continents.
The team found that airborne pollen can account, on average, for 44% of the variation in infection rates. In some cases, humidity and air temperature also play a role. During periods with no travel restrictions, infection rates were on average 4% higher for each increase of 100 grains of airborne pollen per cubic metre. During the observation, concentrations of up to 500 pollen grains per cubic metre per day were recorded in some German cities - resulting in an overall increase in infection rates of more than 20%. In regions where the lockdown was in force, infection rates were on average lower despite airborne pollen.
Previous studies1 have shown that high pollen concentrations lead to a weaker immune response to viruses responsible for respiratory diseases. This is because if airborne pollen concentrations are high, and pollen grains are inhaled with virus particles, fewer antiviral interferons are generated. Therefore, on days with high pollen concentrations, there can be an increase in the number of respiratory diseases. This also applies to COVID-19. Whether or not individuals are allergic to different types of pollen matters little.
"It is not easy to avoid exposure to airborne pollen," say the study authors. "However, people in high-risk categories should be informed that a high concentration of airborne pollen increases susceptibility to viral respiratory tract infections, thus the chance of getting COVID-19."
According to the researchers, when studying the spread of the SARS-CoV-2 virus, environmental factors such as the concentration of pollen in the air must be taken into account. Increased awareness of these effects is an important step in preventing and mitigating the impact of the pandemic.
How can vulnerable people protect themselves? According to the authors of the study, people at high risk should monitor a pollen forecast, avoiding going outside when the concentration in the air is highest. In addition, it may be useful to wear masks that physically filter out pollen particles.
Athanasios Damialis, Stefanie Gilles, Mikhail Sofiev, Viktoria Sofieva, Franziska Kolek, Daniela Bayr, Maria P. Plaza, Vivien Leier-Wirtz, Sigrid Kaschuba, Lewis H. Ziska, Leonard Bielory, László Makra, Maria del Mar Trigo, COVID-19/POLLEN study group, Claudia Traidl-Hoffmann. Higher airborne pollen concentrations correlated with increased SARS-CoV-2 infection rates, as evidenced from 31 countries across the globe. Proceedings of the National Academy of Sciences Mar 2021, 118 (12) e2019034118; DOI: 10.1073/pnas.2019034118 Technical University of Munich (TUM). "COVID-19 risk increases with airborne pollen, study finds: Increased pollen concentrations correlate with higher SARS-CoV-2 infection rates." ScienceDaily. ScienceDaily, 9 March 2021
1. Gilles S, Blume C, Wimmer M, Damialis A, Meulenbroek L, Gökkaya M, Bergougnan C, Eisenbart S, Sundell N, Lindh M, Andersson LM, Dahl Å, Chaker A, Kolek F, Wagner S, Neumann AU, Akdis CA, Garssen J, Westin J, Van't Land B, Davies DE, Traidl-Hoffmann C. Pollen exposure weakens innate defence against respiratory viruses. Allergy. 2020 Mar;75(3):576-587. doi: 10.1111/all.14047. Epub 2019 Nov 7. PMID: 31512243.