Pollen Explains Flu-Like and COVID-19 Seasonality

Abstract

<jats:p>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 &lt; 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 &lt; 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.</jats:p>

Competing Bioaerosols May Influence the Seasonality of Influenza-Like Illnesses, including COVID-19. The Chicago Experience

“…The data presented herein are consistent with those presented earlier by others [ 3 , 4 ], namely, the incidence of ILIs falls as pollen count rises. Because the data of the present study derive from an urban area in North America (Chicago, IL, USA: latitude 41.85003, longitude −87.65005) whilst those of the earlier study derive from North Central Europe (Helmond, the Netherlands: latitude 51.48167, longitude 5.66111), it appears the inverse relationship may be generally valid.…”

“…The data presented herein are consistent with those presented earlier by others [3,4], namely, the incidence of ILIs falls as pollen count rises. Because the data of the present study derive from an urban area in North America (Chicago, IL, USA: latitude 41.85003,…”

“…Pollens are fertilizing elements of flowering plants whilst mold spores are reproductive elements of fungi. In published studies [ 3 , 4 ], pollens alone were counted and related to ILIs. Left uncounted were mold spores, important seasonal contributors to the total bioaerosol burden.…”

“…However, if direct antiviral activity is an attribute of the bioaerosols themselves, then one would not expect, a priori, significant disparity between individual susceptibilities to severe flu or COVID-19 [ 44 , 45 ]. As indirect means, others have proposed pollens stimulate the human immune system in such a way as to either potentiate endogenous antiviral activity or elicit a protective allergic response [ 3 ]. Against these proposals, asthma does not confer protection against either influenza or COVID-19 [ 46 , 47 , 48 ].…”

“…Influenza-like illnesses (ILIs) attributable to influenza viruses and to coronaviruses are sharply seasonal [ 1 , 2 ]. Importantly, recent data from the Netherlands indicate there exists an inverse relationship between the seasonal incidence of ILIs, including COVID-19, and pollen count [ 3 , 4 ]. To discern whether such a relationship might be the case generally, pollen count in Chicago was related to ILIs reported by local emergency departments.…”