People who are immunocompromised will be offered a third dose of a Covid-19 vaccine from next week.
Health care professionals will identify patients who need a third dose.
People who have a functioning immune system need just two shots of a Covid-19 vaccine to reach the required level of immune response.
But those who have a compromised immune system, such as certain cancer patients or people on certain medication require three shots to reach the required level of immune response.
The HSE says it is not the beginning of their general booster campaign.
Consultants will identify patients who need a third shot and will start contacting them from Wednesday with appointments starting on Friday.