Watch: Tree pollen may spread coronavirus
Hay fever season is always difficult for those with allergies. Amid the coronavirus pandemic, however, circulating pollen may be nothing to sneeze at.
Scientists from the University of Nicosia in Cyprus noticed a correlation between coronavirus infection rates and high pollen concentrations.
Pollen grains can carry hundreds of viral particles at a time, with trees alone releasing up to 1,500 grains per cubic metre during the peak of hay fever season.
To better understand pollen's role amid the pandemic, the scientists used a computer model to mimic how the grains move from a willow tree.
If coronavirus particles that are circulating in the air "stick" to pollen, airborne grains may contribute to the infection's spread, results suggest.
"A light breeze" may then "transport" the coronavirus, turning crowded spaces into a potential "superspreading" event.
In the UK, willow's pollen season generally lasts from early March to mid May. Oak, pine and lime trees continue to release the allergen throughout June and July, however.
"To our knowledge, this is the first time we show through modelling and simulation how airborne pollen micrograins are transported in a light breeze, contributing to airborne virus transmission in crowds outdoors," said study author Professor Dimitris Drikakis.
The coronavirus is a so-called RNA virus. In simple terms, RNA is a precursor to the more well-known DNA.
Pollen "pellets" are known to "capture RNA viruses", according to the Nicosia scientists.
After creating a computer-based willow tree, the scientists simulated a range of outdoor gatherings, with 10 to 100 people, some of whom were shedding coronavirus particles.
The people were then exposed to 10,000 pollen grains.
"One of the significant challenges is the re-creation of an utterly realistic environment of a mature willow tree," said co-author Dr Talib Dbouk.
"This included thousands of tree leaves and pollen grain particles, hundreds of stems and a realistic gathering of a crowd of about 100 individuals at about 20m (65ft) from the tree."
The Nicosia scientists adjusted the model to the temperature and humidity of a typical US spring day, with the wind speed set at 4km (2.5 miles) an hour.
The results, published in the journal Physics of Fluids, suggest pollen could pass through a crowd in under one minute.
The grains may then "pick up" coronavirus particles from people who are shedding the infection.
"In the case of high pollen grains concentrations in the air or during pollination in the spring, the social distance of 2m (6.5ft) does not hold as a health safety measure for a crowd outdoors," wrote the scientists.
"Thus, the public authorities should revise the social distancing guidelines."
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