Health Canada has approved Moderna's updated COVID-19 vaccine targeting the Omicron BA.4/BA.5 subvariants for use in adults.

The regulator said Thursday it determined that the latest Moderna Spikevax booster is safe and effective.

The updated vaccine is a combination of two strains, also known as a "bivalent" shot. It contains both the original vaccine formulation and protection against the Omicron subvariants BA.4 and BA.5.

"Clinical trial results showed that a booster dose of the bivalent Moderna Spikevax vaccine triggers a strong immune response against both Omicron (BA.4/BA.5) and the original SARS-CoV-2 virus strains," Health Canada said in a statement.

Side effects were mild and similar to the previously approved version of the vaccine, according to Health Canada.

Doctors recommend that Canadians keep up to date with COVID-19 vaccinations to protect against serious illness and complications of infection.

The bivalent vaccines are expected to offer better protection against Omicron, which Health Canada said is currently the most dominant strain of the virus circulating in the country and worldwide.

Dr. Lynora Saxinger, an infectious diseases physician at the University of Alberta, notes there's a significant improvement in protection against severe outcomes with having had a third dose.

"I think it's very important that people be aware that two doses is no longer enough," Saxinger said in an interview. "People who haven't had boosters at all should be getting a fall booster as a major priority."

Dr. Isaac Bogoch, an infectious diseases specialist at the University of Toronto, welcomed having another tool in the vaccine toolbox. "But additional vaccines won't do a lick of good if people don't take them," he said.

Bogoch called it fantastic that so many people are eligible for a booster.

"I hope people get those vaccines," he said. "But it's especially important for people who are at greater risk for severe infection. This is exactly who we're seeing in hospital: People over the age of 60 years, and people with underlying medical conditions that put them at greater risk."

In September, Health Canada approved an earlier version of Moderna's COVID-19 vaccine targeting the Omicron BA.1 subvariant.

Canada's National Advisory Committee on Immunization (NACI) recommends that the updated vaccine be offered to adults who are recommended to receive a fall booster dose.