Increasing Pollen Rates Affect COVID Infection Rates

High risk groups can protect themselves by watching pollen forecasts and wearing masks

March 15, 2021

A new study found that pollen—which is also being affected by climate change—can help explain additional COVID infection rates during the Spring when tree allergies become dominant.  How much of an impact?  Based on these data, an increase of pollen abundance by 100 grains per cubic meter of air resulted in an average increase in infection rates of 4 percent. The results are published in PNAS titled Higher Airborne Pollen Concentrations Correlated with Increased SARS-CoV-2 Infection Rates.

“We tested for relationships between SARS-CoV-2 infection rates and pollen concentrations, along with humidity, temperature, population density,” said Lewis Ziska, PhD, professor of Environmental Health Sciences at Columbia Mailman School of Public Health and a co-author. “We found that spring pollen, sometimes in synergy with humidity and temperature, explained, on average, 44 percent of the infection rate variability. Without lockdown, an increase in pollen abundance resulted in a 4 percent average increase in infection rates. A strict lockdown cut the increase by half.”
In the spring of 2020, the outbreak of the coronavirus pandemic appeared to coincide with the tree pollen season in the northern hemisphere. These observations prompted an international team headed by researchers at the Technical University of Munich (TUM) and to conduct an extensive investigation. The team collected data on airborne pollen concentrations, weather conditions and SARS-CoV-2 infections – taking into consideration the variation of infection rates from one day to another and the total number of positive tests. In their calculations, the team also included data on population density and the effects of lockdown measures. The researchers analyzed pollen data from 130 stations in 31 countries on 5 continents.

The team showed that in some German cities, concentrations of up to 500 pollen grains per cubic meter per day were recorded during the study – which led to an overall increase in infection rates of more than 20 percent. In regions where lockdown rules were in effect, however, the infection numbers were on average only half as high at comparable pollen concentrations.

High pollen concentrations lead to a weaker immune response in airways to viruses that can cause coughs and colds. When a virus enters the body, infected cells usually send out messenger proteins. This is also the case with SARS-CoV-2. These proteins, known as antiviral interferons, signal nearby cells to escalate their antiviral defenses to keep the invaders at bay. Additionally, appropriate inflammation response is activated to fight the viruses.

But as the researchers explained, if airborne pollen concentrations are high, and pollen grains are inhaled with the virus particles, fewer antiviral interferons are generated. The beneficial inflammatory response itself is also affected. Therefore, on days with a high concentration of pollen, it can lead to an increase in the number of respiratory illnesses. This also holds true for COVID-19. Whether individuals are allergic to the different pollen types is irrelevant.

The author caution that people in high-risk groups should, therefore, be informed that high levels of airborne pollen concentrations lead to an increased susceptibility to viral respiratory tract infections. They can protect themselves by watching pollen forecasts and by wearing dust filter masks. They further emphasize that when studying the spread of SARS-CoV-2, environmental factors such as pollen must be taken into account. Increased awareness of these effects are an important step in preventing and mitigating the impact of COVID-19.

Co-authors are Athanasios Damialis, Stefanie Gilles, Franziska Kolek, Daniela Bayr, Maria Plaza, Sigrid Kaschuba, Vivien Leier-Wirtz, and Claudia Traidl-Hoffmann, Technical University of Munich; Mikhail Sofiev, Viktoria Sofieva, Finnish Meteorological Institute, Helsinki; Leonard Bielory, Rutgers University; László Makra, University of Szeged, Hungary; and Maria del Mar Trigo, University of Malaga, Spain.