The HSE is hoping to offer every adult a booster vaccine by the end of January or early February.
More than 300 thousand boosters have been administered over the last week for the first time.
Nearly 50 thousand were given out yesterday alone - as people over 40 became eligible.
HSE vaccines director, Damien McCallion, says they're finalising plans to offer boosters to younger people.
He says once demands ease from older age groups centres, GPs and pharmacies will offer the vaccine to younger age cohorts.
Booster jabs are currently available to all adults via their GP, though doctors are being asked to prioritise vulnerable and older people.