The National Immunisation Advisory Committee (NIAC) has recommended that the AstraZeneca vaccine can be used for those aged 70 years and older, in fresh advice to the Department of Health.
It has also said that there should be no delay in vaccination.
The new recommendation may clear the way for the AstraZeneca vaccine to be used for this older age group.
So far, over 100,000 of people in this age group have been given a first dose, mainly the Pfizer vaccine.
But there are a total of close to half a million people in Cohort 3 - those aged 70 and older - to be vaccinated.
The new advice updates the original advice from NIAC on 2 February last which recommended that the AstraZeneca vaccine could be used for those aged 65 and older, but where possible and timely, an mRNA vaccine such as Pfizer or Moderna should be used.
After receiving that advice, Chief Medical Officer Dr Tony Holohan recommended to the Government that the AstraZeneca vaccine should not be used for those aged 70 years and older.
Deputy CMO Dr Ronan Glynn is expected to give a revised view to Government shortly, after receiving the new recommendation from NIAC.
NIAC issues its advice to the CMO on vaccines, and the CMO then advises the Government.
Meanwhile, Social Democrats co-leader Roisin Shortall has called on Minister for Health Stephen Donnelly to publish a plan for the rollout of a mass vaccination programme.
Speaking on RTÉ's Morning Ireland, Ms Shortall said that while various priority groups have been given assurances "it would be good to see the plan set down on paper".
She said that 12,000 vaccines are being administered each day and once supplies increase next month there will be a need to ramp it up to 35,000 doses a day.
She said Mr Donnelly needs to give assurances that "everything is in place" for a larger rollout, including that locations of mass vaccination centres are firmed up and the necessary staff are available.
She said that while it is important to recognise the volatility in the supply of vaccines, the messaging could be better for the over 70s and those identified as Cohort 4 with certain medical conditions.
Ms Shortall said that people are waiting anxiously and there is a concern that expectations are being raised without clarity around the timescale involved in waiting for a vaccine.
She said the Government needs to continue at EU level to press for greater efforts to access vaccines from suppliers and for an early decision on approval of the Russian Sputnik V vaccine.
