A measles alert has been issued by public health doctors after two cases of the disease - one involving an adult - were confirmed in Dublin.
It has also led to renewed warnings to families travelling to mainland Europe on summer holidays to ensure they are fully vaccinated against measles.
The HSE said measles was diagnosed in an adult and a child who returned to Dublin after being in mainland Europe.
Measles has led to 31 deaths across Europe this year.
The two patients attended various hospitals in Dublin, which could have exposed others to the infection.
"Measles can be a serious illness and is highly infectious. The best protection is to be fully vaccinated with two doses of MMR (Measles, Mumps, and Rubella) vaccine," said Dr Helena Murray, a specialist in public health medicine.
There is a possible risk of measles to people who may have been in the same healthcare setting as these two cases during the infectious period.
People at increased risk are those who are not fully vaccinated with two doses of MMR vaccine, or have not had measles in the past. The risk of measles is for up to 21 days after contact with a case of measles.
"If you think you may have measles, stay at home and phone your GP for advice," she said.
Currently, the HSE is aware that the two measles cases attended the following healthcare settings while they were most infectious:
The HSE asked people not to contact the hospitals if they may have come into contact with a case of measles but to seek advice from their GP if they become unwell.
It revealed that its public health department has sent an alert to all hospital EDs and GPs in Dublin, Kildare and Wicklow to inform them to be vigilant about measles.
The advice is:
lAll children should get the MMR vaccine when they are aged 12 months. If any child aged over 12 months has missed this vaccine they should get it now from their GP.
All children should get a second dose of MMR vaccine when they are four to five years old or in junior infants at school.
If any child in senior infants or older has missed this vaccine they should get it now from their GP.
Adults under 40 years old who have not had measles or have not received two doses of the MMR vaccine should contact their GP to get the MMR vaccine.
lAdults over 40 years of age may sometimes be at risk and if such adults never had measles nor a measles-containing vaccine they should consider getting the MMR vaccine from their GP.
Measles symptoms include:
• High fever
• Runny nose
• Red eyes
• Red rash that starts on head and spread down the body - this normally starts a few days after onset of illness. The rash consists of flat red or brown blotches, which can flow into each other. It lasts about four to seven days
• Vomiting, diarrhoea and stomach pain may also happen.
Measles outbreaks have been reported in Romania, France, Greece and Italy.