An outbreak of measles in Dublin city has spread, and is now affecting Meath.
The HSE says it has now had seven cases confirmed, and has notified all emergency departments and GPs in Dublin, Kildare and Wicklow.
It comes a week after initial confirmation last week of two cases in north Dublin city.
People who have not had the MMR vaccine are being warned that measles can be highly contagious and a serious illness.
In a statement, the HSE said: "The Measles Outbreak Control Team continues to investigate and advise on measures to control the further spread of this potentially serious illness.
"Alerts regarding measles have been sent to all Emergency Departments and General Practitioners (GPs) in the affected areas. Work is ongoing in identifying close contacts of cases who are being notified and advised by Public Health."
Unimmunised pregnant women who have been exposed to the infection are being urged to seek medical advice.
Meanwhile, anybody who has symptoms suggestive of measles - which include high fever, cough, runny nose, red eyes and red rash - is being urged to stay at home and contact their GP by phone.
More information about measles can be found here.