The COVID-19 booster vaccination program is set to begin today despite more than 100,000 Australians having already received their third jab. 

The booster vaccination program allows anyone over 18 years old who received their second dose of a COVID-19 vaccine at least six months ago to have a third shot. 

While today marks the formal beginning of the booster program, as of Saturday more than 173,000 boosters had already been administered.

At this time, only the Pfizer vaccine is currently being offered for booster shots and it is believed the vaccination of young children is unlikely to begin this year.