Higher concentration of airborne pollen is associated with increased novel coronavirus infection rates, according to a study that used data from 31 countries across five continents. Researchers at the Technical University of Munich (TUM) and the Helmholtz Zentrum Munchen in Germany noted that people in high-risk groups can protect themselves by watching pollen forecasts and wearing dust filter masks.

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. The researchers also included data on population density and the effects of lockdown measures.

The study, published in the journal Proceedings of the National Academy of Sciences, analysed pollen data from 130 stations in 31 countries on five continents. The team showed that airborne pollen can account for, on average, 44 per cent of the variation in infection rates, with humidity and air temperature also playing a role in some cases.

During intervals without lockdown regulations, infection rates were on average four per cent higher with every increase of 100 grains of airborne pollen per cubic meter, the researchers said. In some German cities, concentrations of up to 500 pollen grains per cubic meter per day led to an overall increase in infection rates of more than 20 per cent, they said.

However, in the regions where lockdown rules were in effect, the infection numbers were on average only half as high at comparable pollen concentrations, according to the study. The researchers explained that high pollen concentrations lead to a weaker immune response in airways to viruses that can cause coughs and colds.

They noted that when a virus enters the body, infected cells usually send out messenger proteins, adding this is also the case with SARS-CoV-2. These proteins, known as antiviral interferons, signal nearby cells to escalate their antiviral defences to keep the invaders at bay.

Additionally, appropriate inflammation response is activated to fight the viruses, according to the researchers.
However, the researchers said, 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, they said. The study suggests that a high concentration of pollen can lead to an increase in the number of respiratory illnesses, including COVID-19.

Whether individuals are allergic to the different pollen types is irrelevant, the researchers said. “You cannot avoid exposure to airborne pollen,” says Stefanie Gilles, first author of the study. “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,” Gilles said.

The researchers noted that when studying the spread of SARS-CoV-2, environmental factors such as pollen must be taken into account. Increased awareness of these effects is an important step in preventing and mitigating the impact of COVID-19, they added.

Claudia Traidl-Hoffmann, study author and a professor of environmental medicine, advises people at high-risk to monitor pollen forecasts. “Wearing a particle filtering mask when pollen concentrations are high can keep both the virus and pollen out of the airways,” Traidl-Hoffmann said.