Covid outbreaks have been linked with the hayfever season by top scientists.High pollen counts can add up to 30% to infection rates, a study has found.Researchers urged those vulnerable to Covid to wear particle-filter face masks when pollen levels are high this Spring.The effect was seen in all types of pollen with the scientists adding "we assume that the pollen effect is relevant for the entire population."It might, however, be more pronounced in allergics, asthmatics, or chronic rhinosinusitis patients, due to an intrinsically weaker antiviral immune response."The study's findings were based on data from 130 sites in 31 countries in five continents and found pollen levels could explain 44% of the changes in Covid's infection rate, or R.