Airborn pollen related to Corona infection

Recently a paper was published about the correlation between airborne pollen and infections with the SARS-CoV-2 virus. This research was done by Thanos Damialis, airobiologist and researcher at Department of Environmental Medicine, Faculty of Medicine at the University of Augsburg, Bayern in Germany. A few questions to learn more about this research project.


Higher airborne pollen concentrations correlated with increased SARS-CoV-2 infection rates, as evidenced from 31 countries across the globe

1. What is your background as a researcher?

The research team (154 co-authors) comprises a multi- and inter- disciplinary team of variable scientific expertise, aerobiologists, immunologists, medical doctors, biologists, physicists, mathematicians, ecologists etc. My personal scientific background is Forestry and Biology: I have been an active aerobiologist since 1996 and I have been working since then on pollen and fungal spores. Since 2003, I have emphasised more on climate change impacts, plant and fungal ecology and environmental health, whereas since 2018 I have been working on the interaction of various environmental and biological parameters, including but not limited to pollen and fungal spores and viruses, meteorological variables and air pollution.

2.What is fascinating about aerobiology?

Aerobiology actually studies something that we most frequently take for granted: the air we breathe. And since we cannot really see what is in there, we often assume that there is nothing, some chemical substances mainly. But the reality is different: there is life!

3. What was the hypotheses of the research?

According to the description of the immunological background and the mechanism behind it, as described in the near past by co-authors of the core team (Gilles et al., 2020, Allergy, ), we hypothesized that higher pollen concentrations would lead to higher numbers of virus infections also in the case of SARS-CoV-2, as observed for the rhinovirus, but other viruses before that too by other researchers.

4. What is the conclusion of the research?

The conclusion of the research is that under certain conditions (above all contact though) virus infection numbers may be increasing as an equation of airborne pollen, but at the same time as an equation of favourable environmental parameters, like air temperature and humidity. Another conclusion is that to get infected you need contact with an infected person. Protecting ourselves (especially higher-risk individuals) by wearing particle filtering masks while having higher pollen concentrations during springtime tree pollen season, protects from the pollen as well as from being infected. During such a pandemic, everyone ought to consult daily the pollen information services in their areas and countries.

5. Was is difficult to collect all the pollencountings from so many countries?

I was personally surprised positively to find out how united the aerobiological community was and is. No, it was not difficult. I am touched by what the scientific community can achieve when it unites forces, even during such a difficult, unprecedented pandemic era.

Image: Pollencountingstations which participated in research (source: PNAS).

6. In which countries was the correlation between pollenconcentration and Covid the strongest?

It was not one of the aims of this study to quantify the isolated effects and the magnitude of effect of each examined parameter, including pollen concentrations. Knowing that the major factor is contact, as frequently expressed by lockdown effects (and population density), we could identify Spain and Switzerland as having some of the strongest pollen effects compared to the rest environmental factors examined. Relatively high pollen effect exhibited also (after isolating from the lockdown variations) the countries of Croatia, Czech Republic, Denmark, Greece and Portugal. In these, pollen concentrations were the most significant factor of the three in total environmental factors that were examined in this setup.

7. Pollenwise, every season is different. The Alder peak was pretty high in 2019 and 2021 in the Netherlands compared to 2020. Also the birchpollenpeak varies a lot annually. The grasspollen season is more or less fixed, but shows many weekly peaks depending strongly on the weather. Was 2020 a “normal/average” pollenyear? Or did you have to take in account abnormalities (besides Covid ofcourse) ?

Indeed, we observed this too. We will observe it too in 2021. As far as we see the patterns to date, 2020 was a relatively ‘mild’ pollen season, at least in temperate climates in central Europe, like Germany and the Netherlands. In contrast, the 2021 pollen season so far seems to be more intense, but without being able to forecast if indeed will be a ‘harsh’ pollen year. We did not take into account any such ‘abnormalities’, we preferred to use daily raw pollen concentrations so as to try to assess the genuine pollen effect magnitude.

Image: Dried pollengrain of Alder (3DPollenproject).

8. Which type of pollen showed the strongest correlation?

Since we ran the study during February to April 2020, we anyway referred mainly to tree pollen. We preferred not to break down the analyses per pollen type, as this would complicate the results even more. The main aim at that stage was to potentially confirm that airborne pollen can be also a significant variable in the pandemic equation. The magnitude and the exact mechanism, as well as additional favouring or confounding factors are yet to be explored.

9. The floweringcalendar of Sydney and Japan look completely different compared to the European flowering calendar. Also within Europe are differences. Alder and Birch will flower earlier in central and eastern Europa compared to the Netherlands or Belgium. The spread of Covid over the world also has a specific, pretty unique, dynamic. How did you take this into account comparing the pollencountings and Covid?

As mentioned in the previous question too, for this reason exactly, we preferred to analyse any potential relationships only with the total pollen concentration per day and not per pollen type. While there are similarities, to an extent, in the diversity of some plant taxa and therefore their pollen for the winter to springtime species, their abundances indeed and their temporal occurrence may be very different among continents, also countries, even within the same country when they are climatologically diverse, as in Spain or France or Germany. It is therefore worth continuing the research as per different pollen types.

10. Did you find a bigger increase of Covid by patients who have been diagnosed for Allergic rhinitis compared to not diagnosed with Allergic rhinits?

This is still to be explored. Unfortunately, by that time there was no information on the atopy status of the infected cases as they were collected from the Health organisations per country. Follow-up studies will elucidate this but, to date, there is no known higher risk of allergic individuals to be more susceptible to the SARS-CoV-2 virus.

11. Many people have been wearing facemasks, more often inside than outside, how did you consider this aspect for your research?

This is indeed a challenging aspect for any follow-up studies, as it will change the baseline and the magnitude of the effect of the pollen but also other parameters, including humidity and air pollutants. However, please note that by the time the research was conducted and data collected, nobody yet was wearing masks and even the lockdown measures were applied not soon enough in some regions, which allowed us to clearly identify variable environmental effects and their combined magnitude.

12. To stay indoor is usually a good advice during a pollenpeak, so a lockdown might result in a lower pollen exposure. Lockdown-policy varied a lot between countries. What was the impact of  lockdowns on the research?

Lockdown was a major factor defining the infection rates worldwide. This was expected, as contact is the main reason for potentially being infected. Overall, the lockdown was proven to be more efficient when it was adopted soon enough (before the infection cases rise too high), rather than if it would be stricter. Regarding the pollen effect, under lockdown measures, with comparable pollen concentrations, infection rates were half of those without any lockdown. In other words, this means that pollen would still exhibit an effect even after adoption of lockdown measures, but we would need about double the quantity of pollen for the same infection rates.

On the other hand, scientific results alone are not the ones to define policy and decision making. A multi-factorial analysis has to evaluate the optimum scenario during such a pandemic, including (apart from the obvious human health major factor combined with environmental parameters) also societal needs, sociopsychological factors, financial elements, long-term sustainability of national economies etc.

13. The type of vegetation, like treespecies, grasses and herbs,  directly around a pollencountingstation can vary a lot. Did you find any interesting differences in big countries with many countingstations like Germany and the US?

This is exactly what we observed with our analysis too. In bigger countries (but also in climatically diverse countries too, as is the case of the Netherlands too), it was more difficult to identify and even worse to quantify any environmental effect (including that of pollen) on the virus infections. This is why in some obvious cases, like the USA, we did not manage to allocate any significant effect of pollen, even lockdown. For this, we adopted two different longitudinal approaches for the analysis, one (Fig. 5) focusing exclusively on the no-lockdown regime and after the steep increase of the pandemic, so as to check for the full pollen effect. Then, we could identify it even in so diverse and large countries, as France, Germany, Italy etc.

14. Can you explain the correlation between pollenconcentrations and Covid from a biological  point of view? What happens in the body?

When we are exposed to a virus during a pollen season peak, then pollen downregulate the antiviral interferon response of the airways. The detailed mechanism is shown in the recently article by Gilles et al. (2020; Allergy;, which was based on in-vitro and in-vivo experiments, as well as real-life human cohorts.


For more information about this research, check the