Under-35s can also opt to get a Johnson and Johnson vaccine in a pharmacy.
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.
Prof. Loscher says today is a positive day for the rollout.
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