The HSE's online portal for Covid-19 vaccines opens for the 30 to 34 age-group today.
34-year-olds can sign up for an MRNA jab this morning, with 33-year-olds tomorrow, down to 30-year-olds on Sunday.
Under-35s can also opt to get a Johnson and Johnson vaccine in a pharmacy - with 80,000 jabs being distributed to outlets from today.
Professor of immunology in DCU, Christine Loscher, recommends either option.
"My advice would be whichever one you can get quicker you should take.
"There's very good evidence of both vaccines in terms of efficacy against the Delta variant, which we're very concerned about at the moment.
"Register on the HSE portal, register with you local pharmacy, whichever vaccine you can get first would be the one I'd recommend you to get."
You can register at https://vaccine.hse.ie/
