People aged from 25 to 29 years are now eligible for a Covid-19 vaccine from Thursday.
It is the latest expansion of Northern Ireland's vaccination programme.
Appointments are available to book online at the Health and Social Care booking website and by telephone on 0300 200 7813.
The Department of Health (DoH) said vaccine supplies remain limited and there will be about 20,000 slots available weekly.
The limit is to help manage the availability of the Pfizer vaccine after regulators said under 40s should be given an alternative to the AstraZeneca vaccine, the DoH said.
However anyone in that age group can still make an informed decision to have AstraZeneca.
DoH added that early indications showed uptake was high.
Earlier this week it was reported that more than one million people in Northern Ireland have received a first dose of a Covid-19 vaccine.
NI Health Minister Robin Swann said the announcement for the 25-29 age group was "welcome news" and "further testament to the successful delivery of the vaccination programme in Northern Ireland".
"Vaccination is vital in helping us move through this pandemic and there is no doubt that there are people in Northern Ireland alive today because they have been vaccinated," he said.
"Next week we will see further easing of restrictions with the re-opening of licensed and unlicensed premises indoors, the remainder of tourist accommodation and the further relaxation to the rules over visiting indoors.
"This has been made possible because of the success of the vaccination programme and the majority of people acting on the public health advice."
On Wednesday, it was announced that surge testing and jabs would be expanded to six new areas of concern in England to combat the spread of the Indian Covid variant.
Earlier this week, it was reported there had been a slight increase in the number of Indian variant cases in Northern Ireland to 16.
Mr Swann added:"I know there are some younger people that think they don't need the vaccine but we have seen what this virus can do and with variants now in the mix we all need to protect ourselves and those around us."
Chief medical officer Dr Michael McBride said that by getting the vaccine, people were protecting "not only" themselves, but family and friends.
The Department of Health said that in line with the latest Joint Committee on Vaccination and Immunisation (JCVI) advice, "anyone under the age of 40 can book their vaccination at a trust centre in order to receive the Pfizer-BioTech vaccine".
It said for anyone under 40 who wishes "to make an informed decision to receive the AstraZeneca vaccine there are slots available at the SSE Arena and at participating community pharmacies".
The department said people making bookings "are asked to be patient, as demand for appointments is expected to be strong".
It said the "ongoing roll-out of the vaccination programme will continue to be dependent on the availability of vaccine supplies".