Immunocompromised people aged 12 and over will get a booster dose of a COVID-19 vaccine, the Government has confirmed.
New advice also says pregnant women can receive a vaccine at any stage of pregnancy, rather than just between 14-36 weeks.
The changes follow the latest advice from NIAC.
An extra dose of a vaccine for immunocompromised people marks the start of a booster vaccine campaign.
They'll receive a dose of an mRNA vaccine - either Pfizer or Moderna - 'a minimum' of two months after their last dose.
It means a third dose for those who've received the Pfizer, Moderna or AstraZeneca vaccines, or a second for those who've received the Johnson & Johnson jab.
They'll receive one of the mRNA vaccines regardless of which vaccine they received previously.
Announcing the change, Health Minister Stephen Donnelly said the measures will be put in place as soon as possible.
He said: "Since the very beginning of this pandemic, we have worked to protect those most at high risk from severe illness and death from COVID-19.
"I hope that the opportunity to receive a third or booster dose of COVID-19 vaccine dose brings comfort and reassurance to people that these vaccines are very safe and effective and offer protection from COVID-19.
“As we move into this new stage of the pandemic, it is more important than ever that all of those eligible for vaccination but who remain unvaccinated or partially vaccinated, should initiate/complete their vaccination course."
It remains unclear whether a booster vaccine campaign will be extended to the general population.
A number of experts have suggested there's no need for a population-wide booster campaign for now.
The WHO has urged rich countries to hold off on booster campaigns until more vaccines are sent to the developing world.