The HSE says it is investigating a confirmed case of measles in someone who spends time in Dublin and Kerry.
All known contacts have been notified, but the HSE says anyone who has not had measles or two doses of the MMR, and may have been in Dublin and Kerry in the week up to and including the May Bank Holiday, may be at risk.
Measles is highly infectious and is spread easily, and the Executive says there is a high chance that individuals who have not been fully vaccinated will develop measles if they are exposed.
If anyone has symptoms - which include a rash, irritability, a runny nose and fever - they are asked to stay at home and phone their GP.
Measles has almost been eradicated from Ireland, but is highly infectious.