There are growing calls for healthcare workers to receive a Covid vaccine booster as soon as possible.
A total of 3,500 healthcare staff are currently out of work due to Covid-related illnesses, a figure that has almost doubled in the past 10 days.
The National Immunisation Advisory Committee (Niac) is meeting today to consider if they should receive a top-up jab.
Professor of Immunology at Trinity College, Kingston Mills, says Niac are taking too long to make decisions.
"The healthcare workers were among the first to be vaccinated way back in February, March. A lot of them got the AstraZeneca vaccine as well, so the immune response to that vaccine is not as strong as the one generated with mRNA vaccines - Moderna and Pfizer - so the immunity will have waned more in these."
Irish Nurses and Midwives Organisation (INMO) General Secretary Phil Ní Sheaghdha wrote to Niac chairwoman Professor Karina Butler on Friday for the second time in a week.
In the letter, Ms Ní Sheaghdha said the risk to healthcare workers "requires additional consideration".
More than 100,000 booster vaccines have been administered so far, these have gone to three different groups: over 80s, people in residential care aged over 65 and those who may be immunocompromised.
Boosters are likely to be extended to more of the population following the Niac meeting in Monday, this is likely to be done in descending age groups while booster vaccines for healthcare workers will also come under consideration.