The National Immunisation Advisory Committee has been 'too slow' in approving booster vaccines for healthcare workers, according to Prof Kingston Mills.
He says it's "absolutely essential" healthcare staff now get a third dose as soon as possible.
NIAC is meeting today to discuss the issue, as the number of healthcare staff out of work due to COVID-19 has sharply increased over the past two weeks.
The HSE has said the number of staff out of work is now 3,500 - nearly double what it was just ten days ago.
There have been growing calls for healthcare workers to now be prioritised for boosters, as many would have received their second dose nine or ten months ago.
That's led to fears the vaccine effects could be waning, while boosters have already been approved for over-60s who got their vaccines later in the year.
Minister Eamon Ryan today said he expects NIAC will now approve vaccines for healthcare workers.
The Green Party leader has said he's not frustrated at NIAC's slow pace, as he's "not going to second guess them" when it comes to decision-making.
However, Prof Mills - Professor of Experimental Immunology at Trinity College Dublin - told Newstalk Breakfast he disagrees with Minister Ryan's assessment.
He said: "I think NIAC has been too slow to implement vaccination for healthcare workers.
"They brought in vaccinations for over 80s and then over 60s - [but] some of the over-60s will be waiting until February to get their booster, as there has to be a six-month gap after the second dose.
“The healthcare workers were among the first to be vaccinated, way back in the early part of the year. A lot of them got the AstraZeneca vaccine as well - the immune response to that vaccine is not as strong as is generated by the mRNA vaccines, Pfizer and Moderna."
He suggested the country will face "greater problems" with COVID this winter if healthcare workers don't get a booster dose soon.
He's sure NIAC will make the decision today, and believes there's "no reason" why a parallel booster programme can't take place for both older people and healthcare workers.
Prof Mills also now believes vaccines should be approved for children, after US regulators gave the green light for 5 to 11-year-olds to be vaccinated.
He said: “About two-three months ago… I predicted there’d be significant numbers of cases in schools when they opened. That’s exactly what has happened.
“The highest cohort per 100,000 cases right now is in the 4 to 12-year-olds. The numbers in secondary schools have dropped significantly because of vaccination.
“The FDA approved a vaccine for under-12s… the EMA is looking at this right now, and it’s expected a decision will be made in the coming days or weeks.
"I’d imagine the EMA will follow suit… then it’s a matter of NIAC looking at this."
Prof Mills says he "really hopes" there won't be COVID restrictions introduced this winter.
However, he said he does worry about some of the high case and hospitalisation numbers being reported.
He said it's still predominantly unvaccinated people ending up in ICU, but the rise in over-50s and vaccinated groups in intensive care is a cause for concern.