Professor Kingston Mills of Trinity College Dublin has said the whole population of adults, right down to age 19, needs to receive a booster shot.
The Professor of Experimental Immunology said he would not see any problem with giving vaccines before a five-month interval is up.
Professor Mills said the benefits, on balance, would be to administer the booster jab now rather than waiting for a particular period of time.
Otherwise the risk of contracting Covid is higher, he said. Speaking on RTÉ's Today with Claire Byrne, he pointed out that childhood vaccines are given at two-month intervals and said there is no risk involved with receiving the vaccine before a five- or six-month period has passed.