Covid 19 risk increases with pollen count

In the spring of 2020, the outbreak of the Corona pandemic in the Northern Hemisphere seemed to coincide with the flight times of tree pollen. These observations prompted an international research team to conduct a comprehensive investigation: the scientists wanted to find out whether there was a detectable link between pollen concentrations in the air and infection rates with SARS-CoV-2.

Pollen as an important environmental factor significantly influences infection rates

Under the leadership of first author Athanasios Damialis, the team at the Department of Environmental Medicine at TUM collected data on pollen concentrations in the air, meteorological conditions and SARS-CoV-2 infections - taking into account variations in the infection rate from day to day or even the total number of people testing positive. The researchers also included data on population density and the effects of lockdowns in their calculations. The 154 researchers analysed pollen data from 130 stations in 31 countries on five different continents.

The team showed that airborne pollen can explain 44 percent of the variance in infection rates on average - but sometimes humidity and air temperature also played a role here. In places without lockdown regulations, the infection rate increased by an average of four percent when the number of pollen in the air increased by 100 per cubic meter. In some German cities, for example, there were at times up to 500 pollen per cubic metre per day during the study period - which led to an overall increase in infection rates of more than 20 percent. However, if lockdown rules applied in the areas studied, the number of infections was halved on average at comparable pollen concentrations in the air.

Pollen count weakens body defenses

The reason: when pollen flies, the body's defence system reacts in a weakened form to respiratory viruses that are responsible for colds and flus. When a virus enters the body, infected cells usually produce signaling proteins - also in the case of SARS-CoV-2. These so-called antiviral interferons call on neighboring cells to strengthen their antiviral defenses to keep the invaders at bay. In addition, a balanced inflammatory response is activated to fight the viruses.

However, if the pollen concentration in the air is high and pollen is inhaled in addition to viruses, fewer of these antiviral interferons are produced. The actually beneficial inflammatory reaction is also influenced. When a lot of pollen is flying, the number of respiratory diseases can therefore increase - this also applies to Covid-19. It does not matter whether those affected suffer from allergies to these pollens or not.

"You cannot avoid being exposed to airborne pollen," says Stefanie Gilles, another lead author of the study. "People belonging to high-risk groups should therefore be informed that increased airborne pollen concentrations make them more susceptible to viral respiratory infections." Athanasios Damialis emphasizes, "When considering the spread of SARS-CoV-2, environmental factors such as pollen must be included in the equation. Knowing these effects opens new avenues for prevention and mitigation of Covid-19."

Protect dust filter masks

So what can people who belong to risk groups do to protect themselves? Last author Claudia Traidl-Hoffmann, professor of environmental medicine, advises consulting pollen forecasts over the next few months. She says, "Wearing dust filter masks when pollen levels are high can keep the virus and pollen alike out of your airways."

Publications:

A. Damialis, S. Gilles et. al: Higher airborne pollen concentrations correlated with increased SARS-CoV-2 infection rates, as evidenced from 31 countries across the globe
In: Proceedings of the National Academy of Sciences of the United States of America (PNAS), March 2021.
DOI: 10.1073/pnas.2019034118

S. Gilles, C. Blume et al:
Pollen exposure weakens innate defense against respiratory viruses.
Allergy. March 2020, 75(3):576-587.
DOI: 10.1111/all.14047