Followup Study Submitted: “Pollen Explains Flu-Like and COVID-19 Seasonality”

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Our followup study to explain the seasonality for COVID-19 by looking at pollen, its immuno-activating (hay fever) and allegedly antiviral properties, has just been made available as preprint v5 on medRxiv: Pollen Explains Flu-like and COVID-19 Seasonality (Work in progress). We processed the comments of 2 review cycles from the journal at which we submitted. In v5, we added the medical explanations of the protective effects of allergic diseases in relation to influenza and COVID-19. Furthermore, we analyzed the relation with meteorological variables as solar radiation, relative humidity and temperature, and analyzed their interaction with pollen and flu-like incidence. The preliminary study is already published by Elsevier Science’s Science of The Total Environment, and the followup paper is submitted to this journal as well.

Media coverage

The popular medical website News Medical, French and Thailand Medical News covered our theory and statistical findings extensively. Yahoo Japan mentions the outcomes, based on an item in the South-Korean newspaper 中央日報 (Central Daily News). Further Naked Science (RU) summarizes and LIFE (RU) and Izvestia (RU) discuss the outcomes. And, Shafaaq (Iraq), Eg24 (Egypt) as well.

Indeed, the appearance of a large amount of pollen in the air can lead to the binding of micro-droplets containing the virus, which slows its spread

Oleg Batishchev, an associate professor of the Department of Biophysics at the Moscow Institute of Physics and Technology” in newspaper Izvestia (RU).

An interview in De Telegraaf, the most read newspaper in The Netherlands, with a bit provocative title invoked big online discussions. Someone posted an English translation of this De Telegraaf article. The item became De Telegraaf’s most read article, the same what happened with the FD item after the preliminary study one month earlier. Next RTL News (NL) had an item (@2m10s) about it as well. It’s clear that COVID-19, hay fever, and multi-cycle pandemics are big subjects, as is the riddle of flu-like-seasonality. We identified the predictor.

The followup study is submitted on May 19, 2020, and is now under review by the respective journal. But, we can at least share the abstract of the paper written with my co-authors Eric van Gorp, professor virology at Erasmus MC, and Ellen Hoogeveen, epidemiologist/internal medicine at Jeroen Bosch Ziekenhuis. The new study is not yet online, but here’s the abstract:

Abstract “Pollen Explains Flu-Like and COVID-19 Seasonality

By Martijn Hoogeveen (corresponding author), Eric van Gorp & Ellen Hoogeveen.

Current models for flu-like epidemics insufficiently explain multi-cycle seasonality. Meteorological factors alone, including associated behavior, do not predict seasonality, given substantial climate differences between countries that are subject to flu-like epidemics or COVID-19. Pollen is documented to be allergenic, plays a role in immuno-activation, and seems to create a bio-aerosol lowering the reproduction number of flu-like viruses. Therefore, we hypothesize that pollen may explain the seasonality of flu-like epidemics including COVID-19 in conjunction with meteorological variables. We tested the Pollen-Flu Seasonality Theory for 2016-2020 flu-like seasons, including COVID-19, in The Netherlands with its 17 million inhabitants. We combined changes in flu-like incidence per 100K/Dutch citizens (code: ILI) with weekly pollen concentrations and meteorological data. Finally, a discrete, predictive model is tested using pollen and meteorological threshold values displaying inhibitory effects on flu-like incidence. We found a highly significant inverse correlation of r(224)= -0.38 (p < 0.00001) between pollen and changes in flu-like incidence corrected for incubation period. The correlation was stronger after taking into account incubation time, which satisfies the temporality criteria. We found that our predictive model has the highest inverse correlation with changes in flu-like incidence of r(222) = -0.48 (p < 0.001) when average thresholds of 610 total pollen grains/m3, 120 allergenic pollen grains/m3, and a solar radiation of 510 J/cm2 are passed. The passing of at least the pollen thresholds, preludes the beginning and end of flu-like seasons. Solar radiation is a co-inhibitor of flu-like incidence, temperature makes no difference, and higher relative humidity associates even with flu-like incidence increases. We conclude that pollen is a predictor of the inverse seasonality of flu-like epidemics including COVID-19, and that solar radiation is a co-inhibitor. The observed seasonality of COVID-19 during Spring, suggests that COVID-19 may revive in The Netherlands after week 33, preceded by the relative absence of pollen, and follows pollen-flu seasonality patterns.

Avatar for Martijn Hoogeveen

Founder and CEO of Icecat NV. Investor through iMerge. PhD Multimedia at Delft University of Technology. Former Professor at Open University Netherlands/Technical Sciences & Environment.

  • commented on June 8, 2020 by Raan

    Indoor confinement adequately explains flu seasonality does it not?

    • Thanks an excellent question.

      The standard misconception is that flu-season is not overlapping Summer, when people are more outdoors.

      The simple answer is therefore: No, being confined indoors is not a good explanation. Flu-season is not absent in "Summer", as is the popular belief, but statistically it starts every year as early as half August, thus in the middle of the Summer in the Northern Hemisphere, when people are still a lot outdoors. The Summer technically ends September 22.

      The more complex answer is: In general, the science consensus is that meteorological variables and seasonal behavior don't sufficiently explain flu-like seasonality. Also behavior associated to the weather can't provide satisfactory explanations for the start and end of flu-like seasonality. Below, still a bit more in detail.

      You might notice in the 2nd paper that, for this reason, we especially discuss the beginning and end of flu-season. The early start of flu-like season (reproduction numbers structurally >1) is half August (wk 33 +/- 1 week) and it can have average temperatures around 17 oC. This is in NL (and many Northern Hemisphere countries) the hottest, most sunny month, on average. People are then still going out, enjoying terraces, having a good time, sometimes on holidays.

      By contrast the ending of flu-like season (reproduction number structurally < 1) around wk 10 (+/- 5 weeks) typically shows far lower temperatures, sometimes as low as 0 oC. People can be out on nice days, but are still a lot of time inside when it's less sunny. Although, in general, we all can agree that behavior - hygiene, social distancing - is important to contain an epidemic/pandemic, seasonal behavior doesn't fit the pattern of flu-like seasonality. Especially, the beginning and ending. Some scientists have argued that kids going back to school after Summer is a major factor in the increase of flu-like incidence. But, then it's not explained why the ending of flu-like incidence is still during school periods. Outside the scope of this research, but something we could analyze in a 3rd study: what's the impact of lockdowns on the amplitude (peak) of flu-like incidence. If we specifically look at lockdown policies, we can observe that independent of the phase of Covid-19 (when it started in a country on the Northern Hemisphere), and independent of the degree of social distancing (Sweden virtually no lockdown, Italy/Spain/France hard lockdowns, Holland: intermediate lockdown), the endings of the covid-19 cycles all seem to be in sync. This doesn't imply that lockdowns are not effective: given seasonality, they are especially effective during flu-like season. And, TW and NZ show that a lockdown can also be instrumental in eliminating the covid-19 epidemic, which is probably easier for a relatively isolated island nation then for us. And, we would hypothesize that the lockdowns are helpful in "flattening the curve", independent of seasonality.


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