A pharmacy in rural Tasmania has administered expired COVID-19 vaccinations to about 600 people over two years.

The state's health department said the issue at Yolla Community Pharmacy in the island's northwest was identified after a review of cold chain processes.

The department is working with the pharmacy to contact people who received a coronavirus vaccine between August 2021 and August 2023.

"Affected persons will be contacted via letter during the first week of January," Director of Public Health Mark Veitch said on Thursday.

"While getting an expired vaccine will not cause harm, it may be less effective in protecting against serious illness or complications from COVID-19 infection."

A department spokesman said about 600 people had been affected.

Dr Veitch encouraged people, especially those who are immunocompromised, who received a COVID-19 vaccine at the pharmacy to speak with their usual doctor about revaccination.

"Whether you need further doses will depend on your age and health," he said.

"It is important to remember that most adults have been advised to get at least one 2023 COVID-19 booster, especially older adults or those with risk factors for serious illness."

The department identified COVID-19 vaccines had been both stored and administered after their expiry date.

Pop-up vaccination clinics will be set up in the area from mid-January.