Eligible people will require a letter from the treating physician as evidence when they attend.

Health Minister Rachel Stephen-Smith said the rollout would make it "easier for at-risk Canberrans to get protected faster".

"The additional primary dose is only available to a specific cohort of vulnerable Australians for whom two doses are not as effective. This is not classified as a booster," she said.

"If you think you are eligible for a third dose you should talk to your doctor and then call our booking line to discuss making an appointment."

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Bookings for third doses can be made through the COVID-19 vaccination booking line on 02 5124 7700, or via the Access and Sensory Clinic for people who may need additional support, including those with a disability or mental health conditions.

Third vaccine doses are also available through general practitioners and pharmacists.

The government has moved on offering the third shot to this specific group on the advice of the Australian Technical Advisory Group on Immunisation.

The advisory group recommends that the third dose should preferably be an mRNA vaccine such as Pfizer and Moderna, and it should be administered two to six months following second dose administration, regardless of which vaccine was administered for the first two doses.

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