Over 400,000 people who have received a first dose of AstraZeneca vaccine could be fully vaccinated sooner than was expected following a recommendation to cut the interval between doses by up to four weeks.
The HSE says revised plans allowing for the interval between AstraZeneca doses to be cut from 12 weeks to as little as eight will be ready within days.
However, the change is contingent on there being sufficient supplies of AstraZeneca available, while the knock-on effects on other parts of the vaccine rollout are also being scrutinised.
Almost half a million people still have to get a second dose of the vaccine between now and mid-August under current plans. Over 32,000 people are expected to receive a second AstraZeneca dose this week, rising to a peak of 124,000 in the third week of July before tapering off the following month.
But following the recommendation by the National Immunisation Advisory Committee (Niac) to shorten the interval between doses, the HSE is now looking at concertinaing these vaccinations into a shorter timeframe.
Trinity College Dublin immunologist Prof Kingston Mills said on Thursday over-60s who received AstraZeneca for their first dose should be offered the Pfizer vaccine for their second dose as this would give them the best protection against virus variants.
However, Niac has made no recommendation for mixing vaccines at this stage, pending further studies into the effectiveness of this approach.
HSE chief clinical officer Dr Colm Henry said the AstraZeneca vaccine had proved very effective "in real-world experience" in the UK "not just in terms of reducing serious illness but also in proxy measures for reducing transmission, reducing the asymptomatic carriage".
Total vaccinations are likely to pass the three million mark on Friday; at least 53 per cent of adults have received a first dose and 25 per cent are fully vaccinated against the virus.
Over 2.9 million vaccine doses had been administered up to Wednesday. More than 2 million people, or 53 per cent of adults, have received a first dose, while 900,000 have received a second dose, or 25 per cent of adults.