The health service will begin reducing the time gap between doses of AstraZeneca from Monday.
The gap between doses will drop to eight weeks on a graduated basis in line with new advice from the National Immunisation Advisory Committee.
Approximately 420,000 people will benefit, starting with people who have been waiting the longest, which the HSE estimates at 14 weeks. Previous gaps between jabs were 16 and 12 weeks for different groups.
HSE chief executive Paul Reid called on anyone with a vaccine appointment to attend, saying: “Please come forward, it really does work.”
The official HSE did-not-attend rate is 4%, with Mr Reid saying it is very low compared with other health appointments.
It was “slightly higher” last week due to the bank holiday, he said.
Rescheduling of appointments can be done but it is complex, the HSE lead on vaccines Damien McCallion said.
Referring to patients of up to 300 general practitioners who are not registered to vaccinate the group seven priority list — those at high risk from the virus due to ill health — Mr McCallion said: “We are very conscious that those medically vulnerable groups are picked up, we are working through a solution.”
Precise numbers cannot be confirmed due to the cyberattack.
GPs have now given 1.3m vaccine doses, he said.
From Monday, about 150,000 over-50s can get the Johnson & Johnson vaccine at 1,000 pharmacies. The portal will open shortly for those aged 35 to 40, but dates are not yet available.
The HSE expects this week to have given between 250,000 and 270,000 doses, and up to 290,000 next week.
Increased vaccine supply is expected towards the end of the month which will boost vaccinations.