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

Pollen exposure weakens the immunity against certain seasonal respiratory viruses by diminishing the antiviral
interferon response. Here we investigate whether the same applies to the pandemic severe acute respiratory syndrome
coronavirus 2 (SARS-CoV-2), which is sensitive to antiviral interferons, if infection waves coincide with high airborne
pollen concentrations. Our original hypothesis was that more airborne pollen would lead to increases in infection rates.
To examine this, we performed a cross-sectional and longitudinal data analysis on SARS-CoV-2 infection, airborne
pollen, and meteorological factors. Our dataset is the most comprehensive, largest possible worldwide from 130
stations, across 31 countries and five continents. To explicitly investigate the effects of social contact, we additionally
considered population density of each study area, as well as lockdown effects, in all possible combinations: without any
lockdown, with mixed lockdown−no lockdown regime, and under complete lockdown. We found that airborne pollen,
sometimes in synergy with humidity and temperature, explained, on average, 44% of the infection rate variability.
Infection rates increased after higher pollen concentrations most frequently during the four previous days. Without
lockdown, an increase of pollen abundance by 100 pollen/m3 resulted in a 4% average increase of infection rates.
Lockdown halved infection rates under similar pollen concentrations. As there can be no preventive measures against
airborne pollen exposure, we suggest wide dissemination of pollen−virus coexposure dire effect information to
encourage high-risk individuals to wear particle filter masks during high springtime pollen concentrations.