People in their 30s are facing a wait of up to a month for their vaccine after they register online.
The HSE portal opens for people aged 35 to 39 from this Sunday.
Up to now, people have been told to expect a two to three week wait; however, that is now expected to stretch to three or four weeks.
On The Hard Shoulder yesterday, HSE Chief Paul Reid warned that the rate of vaccination will slow down in July.
He said that while somewhere between 310,000 and 330,000 doses will be administered this week, that rate could fall to between 200,000 and 220,000 per week in July.
The reduction is due to the decision to reduce the use of the AstraZeneca and Johnson & Johnson vaccines due to the age restrictions placed on their use by the National Immunisation Advisory Committee (NIAC).
Those vaccines are only recommended for use in people over the age of 50 and the HSE will largely rely on Pfizer and Moderna moving forward.
The 710,000 people in the 30 to 39 age group also make it the largest age cohort to be vaccinated so far.
Speaking at yesterday’s COVID-19 briefing at the Department of Health the HSE lead for vaccination Damien McCallion said people in the 35 to 39 age group are “probably looking at a three-to-four-week cycle.”
He said officials would make a decision on when to open the portal to people in their early thirties based on how things go ‘in terms of uptake and other factors’ over the coming weeks.
There were 373 new cases of COVID-19 reported in Ireland yesterday.
The number of people in intensive care has fallen to 18 while the number in hospital stands at 54.
Chief Medical Officer Dr Tony Holohan said there has now been "near elimination" of COVID-19 in the vaccinated population.