They're to be administered to people over 80, and those in nursing homes over the age of 65.
A senior HSE official says only time will tell if everyone will need a booster vaccine.
Booster jabs are going to be offered to everyone over the age of 80 and those over the age of 65 in nursing homes.
They will be given a MRNA vaccine which is Pfizer or Moderna.
The Chief Clinical Officer with the HSE, Dr Colm Henry, says it remains to be seen if everyone else will need one
A third Covid-19 vaccine shouldn't be seen as a booster, according to the US' top advisor on the vaccine.
Dr Anthony Fauci said the extra shot should be seen as part of the roll-out after data from Israel showed it's effectiveness.
And Covid-19 vaccines are available for women at any stage of pregnancy from today.
It follows advice from NIAC for an mRNA jab to be given at any time during the nine months.
The HSE is recommending all women take up the offer, and talk to their GP, obstetrician or midwife if they have any questions.