Only two of the 20 people infected with measles following an outbreak in Limerick city were vaccinated against the disease.
Nine cases involved children aged 0 to 5, none of whom was vaccinated. Four were hospitalised.
Of the remaining 11 cases among 15 to 34 year olds, just two had received the MMR (measles-mumps-rubella) vaccine. Four of this cohort were also hospitalised.
Two doses of the MMR vaccine are recommended to protect against measles, one at age 12 to 15 months, and a second between the ages of four and five. In the case of the Limerick outbreak, 18 people had not received any dose.
The outbreak, which began in January, was imported by a patient who had travelled to the Middle East over Christmas. Nineteen cases have been confirmed in Limerick City since January. There is also a case in Dublin linked to the outbreak.