Health Canada has authorized Moderna's COVID-19 vaccine (also known as Spikevax) for use as a booster shot.
Earlier in the week, the department approved Pfizer-BioNTech's vaccine (Comirnaty) for use as a booster.
Both are mRNA vaccines.
The Moderna booster shot will be half a dose, Health Canada said in a news release on Friday.
That differs from the Pfizer booster, which is a full dose.
"A COVID-19 booster shot is an extra dose of the vaccine given after completion of the primary vaccine series," the news release said.
"The booster shot is designed to help people maintain their protection against COVID-19 over time."
Both the Moderna and Pfizer booster shots are authorized for adults 18 years of age and older to be given at least six months after the regular second dose.
Boosters only recommended for certain populations
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.
It also recommended boosters for front-line health-care workers who had a short period of time between their first two shots, as 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 AstraZeneca 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.
"Evidence continues to show that being fully vaccinated provides strong protection against serious illness, hospitalization and death from COVID-19, including against the delta variants," Health Canada said in its news release.
"People in Canada should consult their local public health guidance, informed by the National Advisory Committee on Immunization, for details on which individuals or groups of people are recommended to receive a booster dose at this time."