Tánaiste Leo Varadkar said the changes did not mean the original plan had been a failure.
The government has announced a change to the National Vaccination Programme which will see the number of cohorts drop from 15 to nine.
It means a change to an age-based system, once those aged 70 years and older, the vulnerable and people with underlying conditions are immunised.
Speaking on RTÉ's Prime Time on Tuesday night, Tánaiste Leo Varadkar said the changes did not mean the original plan had been a failure but that the changes made sense from a scientific point of view.
“Based on advice from doctors and health experts, the 15 cohorts were too many. Trying to stick to it might actually slow it down, so it is better to have nine,” Varadkar said.
“Age is the main predictor of a bad outcome from Covid and that’s why this will be done by age”.
Varadkar said the changes will come into effect as soon as those over 70 and vulnerable people are vaccinated and will make things simpler for the government from an administration viewpoint.
“If you look at this from a scientific point of view," Varadkar said.
"If you've a 35-year-old Garda, are they at more risk than a 60-year-old retail worker? It’s the 60-year-old who is at more risk so that is why we’re doing this."
The government says it plans to administer three million vaccine doses in April, May and June and four out of five adults should have received at least one dose of vaccine by the end of June.
“We are on the road out of the pandemic, it’ll be a bumpy road, but we’re on that road," Varadkar said.
“By the middle of May, over half of adults will have had their first dose.”
