Adults under 30 who do not have underlying medical conditions will be offered an alternative to the Oxford AstraZeneca-vaccine in Northern Ireland.
It comes after the UK medicines regulator said there was a possible link between the jab and "extremely rare" blood clots.
The regulator said the benefits still outweigh the risks overall.
The vaccine has been given almost 500,000 times in Northern Ireland.
The Medicines and Healthcare products Regulatory Agency (MHRA) said it while it has not concluded that the vaccine causes rare blood clots, it says the link is getting firmer.
On Wednesday evening Northern Ireland's Department of Health confirmed that those aged between 18 and 29 years old who do not have an underlying medical condition, would be offered an alternative vaccine when this is available.
The MHRA said the balance of risk for the AstraZeneca vaccine is very favourable for older people but "more finely balanced" for younger groups, who do not tend to suffer serious Covid illness.
It follows on from a review by MHRA which found that by the end of March 79 people had suffered rare blood clots after vaccination - 19 of whom had died.
The regulator said this was not proof the jab had caused the clots, but it said the link was getting firmer.
The UK-wide recommendation to offer alternatives to those aged 29 and younger was made by the Joint Committee on Vaccination and Immunisation (JCVI), an expert independent advisory committee which advises the government.
Professor Wei Shen, chairman JCVI, said the recommendation to prefer other vaccines to AstraZeneca for the under-30s was "out of the utmost caution" rather than because of "any serious safety concerns".
Northern Ireland's Department of Health said it had taken its decision following the updates from the MHRA and JCVI.
It said the Oxford Astrazeneca-vaccine jab will continue to play a "vital role in saving lives, reducing hospitalisations and helping Northern Ireland move out of lockdown".
In a statement the department said: "In line with latest MHRA and JCVI advice, the AZ vaccine will be rolled out on a phased basis to people aged 30 and over in Northern Ireland, as supplies permit.
"It will also continue to be made available to adults of all ages who have underlying health conditions which put them at higher risk of serious illness or death from Covid-19.
"Those aged 18-29 who do not have an underlying medical condition will be offered an alternative vaccine when this is available. This is in line with expert JCVI and MHRA updates issued today.
"These followed reports of an extremely rare potential adverse event of blood clots and low platelet count following vaccination with the first dose of AstraZeneca - although this has not yet been established."
As of Wednesday, the total number of number of vaccines administered in Northern Ireland is 958,783.
By Louise Cullen, health reporter
In Northern Ireland AstraZeneca is the jab dispensed through GP surgeries, pharmacies - who are now coming online, and it will increasingly become the jab that is dispensed at vaccination centres, like the SSE Arena in Belfast.
It accounts for around half the doses in Northern Ireland.
We know that Pfizer was rolled out first and was targeted initially at vaccination centres, healthcare workers and care homes - those groups have now been completed and we're further down that tree of prioritisation and increasingly AstraZeneca has played a big part.
We've got a third vaccine coming, Moderna. That should be getting delivered to Northern Ireland in the next couple of weeks.
The health minister has said that it should be rolling out towards the end of this month - but it is in numbers that are quite small compared to the large allocation that we're getting of AstraZeneca and the reasonably sized allocation that we've had of Pfizer.
The Oxford Astrazeneca-vaccine will continue to be available to everyone aged over 30, and adults of all ages who have underlying health conditions which put them at higher risk of serious illness or death from Covid-19.
The Department of Health said it will be updating health professionals and the public with the new advice.
It will also be reassessing the timeframe for the total vaccine rollout in Northern Ireland.
"The expert advice to people aged 30 and over, and to adults of all ages who are vulnerable to COVID-19, is clear - get the AstraZeneca vaccine to protect yourself from the COVID-19 virus," the department said.
It added the jab would "continue to have a vital role in saving lives, reducing hospitalisations and helping Northern Ireland move out of lockdown".
Meanwhile, the EU's medicine regulator said unusual blood clots should be listed as a very rare side effect of the AstraZeneca vaccine for Covid-19.
After a study looking at 86 European cases, the European Medicines Agency (EMA) concluded the benefits of the vaccine outweighed the risk.
The report reflected data on 25 million Europeans administered with AstraZeneca vaccine.
The EMA could not list specific risk factors such as age or gender, but most blood clot cases were women under 60.