DUBLIN, March 22 (Reuters) - Any European Union restrictions on vaccine exports would be a “retrograde step” that could undermine the supply of raw materials for vaccine production, Irish Prime Minister Micheál Martin said on Monday. Martin told Ireland’s RTE radio that representatives of vaccine-maker Moderna had expressed concern to him that EU export restrictions on vaccines might impact its supply of raw materials for vaccine production. (Reporting by Conor Humphries; Editing by Alison Williams)