The Health Service Executive has urged parents to make sure children are vaccinated against measles following an outbreak in west Cork.
Two children have been hospitalised and another 49 have contracted the virus.
Most of those affected are teenagers who have never received any dose of the MMR vaccine.
Dr Kevin Kelleher said the outbreak was large and rapidly spreading.
He said it is a major concern not only for people in west Cork but for the whole of the country and that vaccination with the MMR is the only way to protect against the disease.
Dr Kelleher also said the summer months increase the risk of coming into contact with measles.
The MMR is routinely provided to babies at 12 months and again at pre-school.
Children younger than 13 who missed out on the vaccine can get it free of charge from their GP, while older children can also get the vaccine free but there may be an administration fee.