The HSE has said it is committed to administering second doses of the AstraZeneca (AZ) Covid-19 vaccine by July 19.
It is estimated that around 450,000 people have received their first jab, but are yet to get their second.
HSE CEO Paul Reid confirmed on Tuesday that the interval between doses was now being reduced from 12 weeks to eight weeks, in line with updated advice from the National Immunisation Advisory Committee (Niac).
Speaking RTE Radio's, Mr Reid said roughly 100,000 people per week between would be getting their second AstraZeneca dose by July 19.
"We should have significant supplies to complete the programme by the week commencing July 19, based on the confirmation that we’ve got from them [AstraZeneca].
"Basically, based on the confirmations that we have, everybody will have received their second dose by that weekend."
The overall national vaccine rollout will not be delayed by the sped-up AztraZeneca programme, he said.
Mr Reid said concerns over the Delta variant were the main reason the accelerated programme had been put in place.
News of the reduced interval comes amid fears over the spread of the Delta Covid-19 variant in the UK.
The rapidly spreading variant is now the dominant strain in the UK — accounting for about 95% of the cases confirmed in the UK last week.
The Delta variant has a transmission rate between 40 and 60% higher than the alpha variant (B117), which already had a 50% higher transmissibility than the original strain of the virus.
On Tuesday, UK prime minister Boris Johnson confirmed that the lifting of coronavirus restrictions in England would be delayed by one month, to allow for the vaccination of a larger portion of the UK population.
A recently published study from Public Health England found that both doses of the AstraZeneca vaccine offered 92% protection against hospitalisation from the Delta variant.
After one dose, the vaccine was just 71% effective at preventing hospitalisation, according to the study.
Given this higher hospitalisation risk after the first jab, the administering of the second dose of AZ has become a priority for health officials on both sides of the Irish Sea.
HSE chief Paul Reid said that, given recent developments in the UK and elsewhere around the Delta variant, now more than ever, it was "hugely important" that people are fully vaccinated.
"You are at your highest level of protection once you have had your second dose. It’s very important that people do come forward for it."