Immunologist Professor Luke O'Neill has said there is more risk of Covid-19 spreading in dense crowds and that the next three or four weeks are critical.
It comes after Chief Medical Officer Tony Holohan said he was "absolutely shocked" by crowds that gathered in parts of Dublin city centre yesterday.
Yesterday, Galway City Council also closed off a popular area by the River Corrib, after large crowds gathered there in recent days.
Dr O'Neill, who is Professor of Biochemistry at Trinity's School of Biochemistry and Immunology, said: "We don't know what is going to happen with the variant that originated in India.