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. Significance Coexposure to airborne pollen enhances susceptibility to respiratory viral infections, regardless of the allergy status. We hypothesized this could be also true for SARS-CoV-2 infections. To investigate this, we tested for relationships between SARS-CoV-2 infection rates and pollen concentrations, along with humidity, temperature, population density, and lockdown effects. Our unique dataset derives from 130 sites in 31 countries and across five continents. We found that pollen, sometimes in synergy with humidity and temperature, explained, on average, 44% of the infection rate variability. Lockdown halved infection rates under similar pollen concentrations. As we cannot completely avoid pollen exposure, we suggest wide dissemination of pollen−virus coexposure information to encourage high-risk individuals to wear particle filter masks during high springtime pollen concentrations.

Ambrosia arrived in Hungary from northern Mediterranean in the 1920s, and by the end of the 20^th century it has become widely distributed. In Southern Hungary (northern part of Serbia‐Montenegro included), Ambrosia pollen concentrations during the peak season are about one order of magnitude higher than the counts in the rest of Europe. The aim of the study is to survey the history of Ambrosia in the Carpathian Basin and analyse some Ambrosia pollen characteristics (season start, duration, average diurnal count and total count) focusing on a medium‐sized city, Szeged, Southern Hungary. The data consists of daily Ambrosia pollen counts for the 15‐year period between 1989 and 2003. Although Ambrosia pollen counts fluctuate considerably, no significant trends can be detected in their temporal course. According to the Makra‐test, the highest pollen counts in Szeged are detected between 20 August and 11 September. This period is in good correspondence with both days comprising over 50 pollen grains per m³, and the main pollination period (MPP).