The weather and our behavior are not the only influencing factors for a coronavirus infection: The pollen count also apparently plays a role, as data from 31 countries now suggest. Accordingly, the infection rates with Sars-CoV-2 increase by an average of four percent if the pollen load increases by 100 pollen per cubic meter. If there is a lockdown, however, this effect is halved. The cause of this effect is probably the reaction of the immune system to pollen-contaminated air: it then reduces the release of antiviral messenger substances and thus increases the susceptibility of the mucous membranes to infection.
When the Covid-19 pandemic spread across the globe at the beginning of 2020, it coincided with the beginning of spring in the northern hemisphere – and thus also with the start of the pollen season. However, it is already known from studies on colds that an increased pollen load can increase susceptibility to some respiratory viruses such as rhinoviruses. As a result, there is more runny nose in spring when there is a high pollen count, even in non-allergy sufferers. “We have therefore examined whether the same applies to the Sars-CoV-2 coronavirus,” explain Athanasios Damialis from the Technical University of Munich and his colleagues.
Increase in infection rates with the pollen concentration
For their study, the international research team evaluated data from 248 pollen measuring stations in 31 countries around the globe. The scientists recorded the pollen concentrations in March and April 2020 and related these values to the daily infection rates in the countries and areas concerned. In addition, they also take into account other factors such as population density, weather and lockdown measures. The evaluations showed that there is a significant correlation. The local pollen load in combination with the weather could explain an average of 44 percent of the variance in infection rates. “The correlation coefficient was positive for all countries and significantly positive for six out of eight,” report Damialis and his colleagues. The effect of the pollen load remained demonstrable even when other factors such as population density and the typically increasing outdoor activities and social contacts in spring were taken into account.
Specifically, it was shown: In places without lockdown regulations, the infection rate rose by an average of four percent if the number of pollen in the air increased by 100 per cubic meter. In some German cities, for example, there were up to 500 pollen per cubic meter per day during the study period – which led to an increase in infection rates of more than 20 percent. However, if there was a lockdown, this rate was halved. Because then, regardless of the effect of the pollen, there are fewer potentially risky contacts in the population. According to the researchers, the pollen count significantly influences the risk of infection with Sars-CoV-2.
Contact with pollen weakens the antiviral immune response
The reason for this lies in the reaction of our immune system to the pollen load: when a virus enters the body, infected cells usually produce antiviral signaling proteins. These so-called interferons alert neighboring cells and induce them to strengthen their antiviral defenses in order to keep the intruders in check. In addition, a balanced inflammatory response is activated to fight the pathogens. If the pollen load in the air is now high, the immune system regulates these defense reactions down so as not to constantly trigger false alarms. This means that fewer antiviral interferons are produced even when the virus comes into contact with the virus and the inflammatory reaction is weakened. According to the scientists, it is very likely that this mechanism also weakens the immune response to the coronavirus. Because this reaction affects the innate immune system, it is independent of a pollen allergy – it also affects people without hay fever or asthma.
This spring, too, the increased pollen count could contribute to an increase in infection rates – if you get too close to infected people. “You cannot avoid being exposed to airborne pollen,” says Damialis’ colleague Stefanie Gilles. “People who belong to high-risk groups should therefore be informed that increased pollen concentrations in the air make them more susceptible to viral infections of the respiratory tract.” But you can protect yourself: FP2 masks filter both viruses and pollen from the air you breathe. “Wearing dust filter masks when the pollen concentration is high can keep the virus and pollen equally away from the airways,” explains senior author Claudia Traidl-Hoffmann from the Technical University of Munich.
Source: Athanasios Damialis (Technical University of Munich) et al., Proceedings of the National Academy of Sciences, doi: 10.1073 / pnas.2019034118