The HSE Covid-19 vaccine portal opens up for registration from today for those aged 35-39.
From today, 39-year-olds can register for vaccination, from tomorrow 38-year-olds can register and so on.
People in their 30s are expected to wait up to a month to receive their first jab after registering on the portal.
This is because the HSE will rely on mRNA vaccines due to AstraZeneca and Johnson & Johnson vaccines’ age restrictions.
They will be offered a Pfizer or Moderna vaccine and will get their second dose within 28 days.
The vaccination of people in their 40s is progressing with over 600,000 registered so far.
The HSE is also promising to provide second doses of AstraZeneca to around 460,000 people, mostly in their 60s, before the week beginning July 19.
Yesterday, HSE chief clinical officer Dr Colm Henry said “all things going well” the 40-year-old cohort should be fully vaccinated by the start of August and the 30-39-year-olds should get their first jab at the beginning of August, meaning they would all be fully vaccinated early September.
This means that those in their 20s could be waiting until the end of September before they have both vaccines.
HSE chief Paul Reid said that while he expected July to be a “strong month”, the numbers administered a dose weekly would be down to between 200,000 and 220,000, with many getting second doses.
Vaccinations have hit a peak, with 330,000 getting a jab this week and 300,000 scheduled for next week.
People receiving their vaccines later than expected may also be due to a higher uptake than expected.
"The 40s uptake is the same as the kind of numbers we saw in the other cohorts,” Dr Henry said on RTÉ’s The Brendan O’Connor Show.
"We saw 99pc in the over 85s, well over 90pc in the over 69s, it’s heading the same way for over the 50s and we are seeing huge numbers and we expect first doses for the 40s to be completed in the coming weeks.
"They are getting the mRNA vaccines so their second dose will be one month later.”