Researchers at the University of Nicosia in Cyprus modelled the spread of pollen from a willow tree through a nearby crowd of people and found that tree pollen could facilitate the transmission of the virus in a crowd of people gathered outdoors.
The scientists found that the larger crowd of people temporarily trapped the airflow and the pollen it carried. They added that this would have the effect of increasing potential contacts between pollen grains and the tiny droplets of saliva generated when people talk, cough, and so on.
The scientists said that they were inspired to conduct their study after noticing correlations between high airborne concentrations of willow oak and white willow pollen in the United States in March-May 2020 and SARS-CoV-2 infection rates.
Dr Dimitris Drikakis, one of the two scientists who worked on this project, said that people should avoid crowd gatherings close to some types of plants or trees, which are known to be very active in pollen grains release during a pollination season.
“The public should be aware of the airborne transmission risks from both indoor and outdoor saliva droplets and the hazards arising from airborne pollen grains outdoors.”
Dr Talib Dbouk and Dr Drikakis together conducted the study from the university’s Defence and Security Research Institute. Their paper has been published in the journal Physics of Fluids.
An earlier study had found that pollen can reduce the production of antiviral molecules in a person’s respiratory tract, which in turn increases their susceptibility to viral infections.
The earlier 2019 study concluded that the ability of pollen to suppress innate antiviral immunity, independent of allergy, suggests that high-risk population groups should avoid extensive outdoor activities when pollen and respiratory virus seasons coincide.