Record-breaking pollen levels linked to increased risk of COVID-19

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Increased pollen concentrations are correlated with higher rates of COVID-19. Hot on the heels of record-breaking European pollen counts, this comes as bad news for a continent struggling with the ongoing health crisis. The large-scale study, conducted by an international team headed by researchers in Germany, suggested people protect themselves by keeping an eye on pollen forecasts and wearing particle filtering masks this spring.

By Amy LeBlanc

Over the past year, we have seen COVID-19 devastate many countries, while leaving others relatively unharmed. We know there are many factors affecting the severity of outbreaks, including population demographics, government measures and environmental factors such as heat and humidity. We already know that there is a correlation between air pollution and increased COVID-19 infection and mortality rates, but now it seems we may also need to worry about another airborne matter: pollen.

The study: COVID-19 risk increases with higher pollen concentrations

Prompted by the concurrence of the first wave of European infections in 2020 with the spring pollen season, an international team headed by researchers at the Technical University of Munich (TUM) and the Helmholtz Centre Munich, decided to investigate whether there is a demonstrable link between airborne pollen concentrations and SARS-CoV-2 infection rates.

When studying the spread of SARS-CoV-2, environmental factors such as pollen must be taken into account. – Athanasios Damialis, TUM

To determine whether pollen is a significant environmental factor influencing infection rates the team collected data on airborne pollen concentrations, weather conditions and SARS-CoV-2 infections, taking into account the effects of lockdown measures. The 154-member team of researchers analyzed pollen data from 130 stations in 31 countries on 5 different continents: a mammoth international effort.

The study concluded that there is indeed a correlation between higher pollen counts and an increase in COVID-19 infections. It seems airborne pollen can account for about 44% of the variation in infection rates, with humidity and air temperature also playing a role in some cases.

Climate change is making pollen seasons worse

It’s worth noting that the effect was strongest when there were no lockdown regulations active in the regions: during intervals without lockdowns, every increase of 100 grains of pollen per cubic meter led to a 4% average increase in infection rates. To put the numbers into perspective: 80 grains per cubic meter is enough to give untreated hay fever patients complaints. During the study, some German cities had pollen concentrations recorded as high as 500 pollen grains per cubic meter, which led to an overall increase in infection rates of more than 20%. In regions where lockdown rules were in effect, however, the pollen effect on infections was only half as high.

You cannot avoid exposure to airborne pollen. – Dr. Stefanie Gilles, TUM

These figures are nevertheless alarming, particularly coupled with the effect of climate change. A long-term study published in PNAS in January based on 30 years’ worth of pollen data from North America found that anthropogenic climate change is resulting in longer and more intense hay fever seasons, with pollen concentrations over 20% higher than they used to be.

Just last week in Belgium, Dr. Marc Piessens (allergist at the Medical Center in Genk), announced that the local measurement center had set a new record for hazel and alder pollen: more than 4,500 pollen grains per cubic meter of air. That’s 500 more than in 2019, the previous record-holding year, and certainly more than enough to have a marked impact on hay fever patients. At these new record-high concentrations, people with hay fever not only suffer from the typical symptoms, like itchy eyes and stuffy noses; many also start exhibiting asthmatic symptoms. And that’s before you take the risk of COVID-19 into account.

How airborne pollen weakens the immune response

The link between pollen and COVID-19 infections may be caused by the pollen particles interfering with the viral immune response in the airways. When viral particles such as SARS-CoV-2 enter the body, cells infected by the virus usually send out messenger proteins called antiviral interferons. This signals to nearby cells that they need to escalate their own antiviral defenses, and also triggers an inflammatory response to fight the virus.

However, evidence from both human and mouse models have shown that if too many pollen grains are inhaled along with virus particles, fewer antiviral interferons are generated. This results in the innate immune response being dampened, and means that days with a high pollen concentrations can lead to an increase in the number of respiratory illnesses, including COVID-19. Unfortunately, this effect occurs irrespective of whether people are actually allergic to the pollen itself.

Wearing a particle filtering mask when pollen concentrations are high can keep both the virus and pollen out of the airways. – Prof. Claudia Traidl-Hoffmann, TUM

“You cannot avoid exposure to airborne pollen,” says Stefanie Gilles, co-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.” Athanasios Damialis, co-first author, emphasizes: “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.”

Read this BioVox article to learn more about how allergy can lead to asthma.

So ,what can vulnerable people do to protect themselves? Claudia Traidl-Hoffmann, last author and a professor of environmental medicine, advises that people in high-risk groups monitor pollen forecasts and make sure to use face masks when outdoors: “Wearing a particle filtering mask when pollen concentrations are high can keep both the virus and pollen out of the airways.”