Health Canada has approved a booster of Pfizer-BioNTech's COVID-19 vaccine for people 18 years of age and older.

The booster is intended to help people who've had their first two COVID-19 vaccine doses to maintain their protection against the virus over time.

The booster is identical to the regular Pfizer-BioNTech vaccine and is to be administered at least six months after the second vaccine dose.

Different provinces have employed different rollout strategies for booster doses. The mRNA vaccines approved in Canada (Pfizer-BioNTech and Moderna) have been used already as a third dose to offer longer-lasting protection to high-risk people — including long-term care home residents and people who are immunocompromised — in several parts of the country.

At the end of October, the National Advisory Committee on Immunization (NACI) recommended boosters for other high-risk groups, including people 70 years of age and older and front-line health care workers who had a short period of time between their first two shots. Evidence has grown over the year showing that expanding the interval between the first and second doses offers better protection.

NACI also recommended boosters for people who received two doses of the Astra Zeneca vaccine, as the mRNA vaccines appear to offer better protection.

NACI says, however, that most people outside those higher-risk groups don't need a booster at this point because there is no evidence of waning protection over time against severe COVID-19 in the general population.