A daily pill can change immune cell memory and reduce allergic reactions like hay fever and thunderstorm asthma, new research shows.

A study led by Monash university found Victorians who took the prescribed medication Oralair for four months in the lead up to allergy season for three consecutive years had retrained immune cells and had long-term protection against allergic reactions.

In 2019, researchers studied 27 Victorians allergic to ryegrass pollen; half of them took the daily tablet consisting of grass pollen under the tongue and the others received antihistamines.

"This is very good news... we compared the samples before and after for any changes in immune memory and what we found is the bases treated with the tablet - their immune cells that responded to ryegrass pollen had changed," Monash University's Central Clinical School lead researcher Menno van Zelm said.

"The cells in the patients that were not treated with the medication had not changed."

He added the early markers in the sublingual immunotherapy (SLIT) will ensure the right patients get the right treatment.

More than 4.6 million Australians suffer from hay fever, which is often triggered by an allergic reaction to outdoor or indoor allergens like pollen and dust mites, according to the Australian Institute of Health and Welfare.

In 2016, Melbourne had the world's largest epidemic thunderstorm asthma event, with thousands of people developing breathing difficulties and at least nine deaths.