"Time will tell" if everyone in Ireland will need a COVID-19 vaccine booster, the HSE's Dr Colm Henry says.
He also says those who are now due to receive a third shot will get either the Pfizer or Moderna vaccines, regardless of whether they received the AstraZeneca or Janssen ones before this.
Dr Henry was speaking after it was announced yesterday that there'll be a further extension of the booster campaign.
An additional dose will be given to care home residents aged 65 and older, as well as people aged 80+ in the community.
It comes in addition to the earlier announcement that immuno-compromised people will also receive an extra dose.
Dr Henry told Newstalk Breakfast these changes reflect “emerging evidence” that there’s waning immunity from the vaccines in certain groups.
He said the HSE's job is to translate NIAC's advice into "real actions and jabs into arms".
He explained: “The booster jab will be the mRNA vaccines - either the Pfizer or Moderna vaccine.
"There’s good evidence that anyone who previously received the AstraZeneca vaccine can get the Pfizer or Moderna [boosters]... it’s safe, effective and stimulates a good immune response.
“The purpose of this booster programme is to build on those gains we’ve seen, and keep people safe - especially those who are most vulnerable in the community.”
Asked whether he expects the general population to receive a booster vaccine, he responded: “Time will tell. I know it’s a frustrating answer for people to hear, but we do rely on the evidence. We want to make sure it’s safe - and it appears giving a booster is safe in the groups we mentioned.
“We need to know it translates into immunity that means something."
He also said he can "definitively" state there are no plans to bring in compulsory vaccination for healthcare workers.
'Lots to be optimistic about'
In terms of the pandemic more generally, Dr Henry said there's now "a lot to be optimistic about".
The average number of daily cases is beginning to fall - the five-day moving average has dropped by 14% over the past week, and by 20% over two weeks
Meanwhile, the case rate among 19-24 has fallen “quite considerably” over the last number of weeks.
Dr Henry said the most important thing is that confirmed cases are translating into fewer hospitalisations and deaths.
He said: “The more serious end of the disease really seems to have taken a kicking by the vaccine programme - it’s protecting people from the most serious manifestation of COVID-19.”
There have been significant concerns this week about the high number of children already out of school due to being a close contact of someone with the virus.
The reopening of schools has also led to a surge in demand for testing, with the HSE temporarily halting walk-in testing as a result.
Dr Henry says the rules for schools are in place to protect people, but he has "no doubt" the rules around close contacts will be reviewed by NPHET soon.
He suggested there's “emerging evidence” that the risk of large volumes of children being taken out of school for 10-14 days “may well be greater than the risk of them catching COVID”.