Children will likely have to be vaccinated for Ireland to reach herd immunity, according to a senior health official.
80% of adults have now received a first COVID-19 vaccine dose.
While 16 and 17-year-olds are expected to be vaccinated soon, there has yet to be official advice issued for younger age groups.
European regulators have already given the green light for the use of the Pfizer vaccine in teenagers aged 12-15, with a decision on the Moderna jab expected shortly.
NIAC has not yet made a final decision on whether teenagers in Ireland should get the Pfizer vaccine.
No vaccine has yet been approved for younger children.
Health officials are continuing to ramp up the vaccine rollout for adults, amid concerns over the Delta variant and growing COVID-19 case numbers.
HSE chief clinical officer Dr Colm Henry says the threshold for reaching herd immunity is higher because of the new strain.
Important from HSE presser: officials say for Ireland to reach herd immunity to Covid, children will likely have to be vaccinated.
Previously, estimate was getting about 60% - 70% of population protected would give herd immunity.
Because of Delta, that's now gone to 85% - 90%.
— Paul O'Donoghue (@paulodonoghue93) July 22, 2021
He said: "It was 60-70% of the population... but because we're dealing with a more transmissible variant, the estimate has gone up to 85-90%.
"If the estimate is that high... it would infer we would need to include age groups going down right to children. That's based on the current estimate of herd immunity that might be needed to deal with the increased transmissibility of Delta."
Herd immunity means a 'critical mass' of people are immune, meaning it's much harder for the virus to spread easily among the community.
HSE CEO boss Paul Reid, meanwhile, today warned that any adults who haven't come forward yet for COVID-19 vaccination are "really putting themselves at risk".
Vaccination registration is currently open to everyone aged 18 or older.
Mr Reid has previously said the HSE will be "immediately" ready to start vaccinating teenagers if they get the sign-off from NIAC.