Moderna's new COVID-19 vaccine isn't a booster: What Canadians should know

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On Tuesday, Health Canada approved an updated vaccine from Moderna that targets a SARS-CoV-2 subvariant.

The new jab was greenlit for Canadians aged six months and above as the world enters its fourth COVID-19 pandemic autumn, and health officials sound the alarm on the rise of new variants — including XBB 1.5, which has become prevalent in 2023.

While COVID indicators have plummeted this year, Canada's chief public health officer Dr. Theresa Tam warned we're not out of the clear, during a technical briefing on Wednesday. Tam added infections and hospitalizations have been on the rise over the past several weeks.

To find out why there's a new vaccine, and what Canadians should know about the new variant, Yahoo Canada spoke with two experts to get the details.

How does the new Moderna vaccine work?

As the virus has evolved in structure, the vaccine needs to be better targeted to the virus receptor protein, explained Earl Brown, Emeritus Professor of Microbiology at the University of Ottawa.

Like previous iterations of Moderna's COVID-19 vaccine, the updated shot uses mRNA. The major difference is this updated vaccine is tailor-made to target the XBB 1.5 variant and contains sequences that offer protection against other Omicron variants.

Health Canada recommends:

• one dose for people five and up regardless of vaccination history

• one dose for children between six months and four years old who have received a dose of a vaccine

• two doses for children between six months and four who haven't been vaccinated against COVID-19

Brown said there are a lot of variations in the virus, "but this vaccine is giving us a leg up on a better match against those variants that are moving among us."

Similarly to last year's bivalent booster doses of the vaccine, which were not identical to what was circulating last year before the boosters, this year's vaccine is not identical to what's circulating now, according to Dr. Allison McGreer, an infectious disease specialist at Mount Sinai Hospital in Toronto.

"But it's close," McGreer said.

It better targets the virus receptor protein of the new dominant subvariant, XBB 1.5.

What do we know about XBB 1.5 subvariant?

Since the start of the pandemic, officials have logged various variants of SARS-CoV-2: Alpha, Beta, Delta and Omicron. Health officials first detected Omicron in November 2021 in Botswana and South Africa. Later that month, Canadian officials confirmed the first case of Omicron in Ottawa.

Since then, Omicron has become the world's most prevalent strain and a crop of subvariants — or viral genomes that contain one or more mutations — have emerged. These include more than a dozen strains of XBB.

"The Omicron variant continues to evolve with XBB subvariants, such as EG.5, continuing to circulate in Canada and globally," Tam said in Wednesday's briefing.

Part of the XBB lineage is the XBB 1.5 subvariant, nicknamed Kraken by a Canadian biology professor. XBB 1.5 is a recombination of two BA.2 sub-lineages — which are also Omicron variants — that emerged last spring.

When the virus comes along, Brown said it infects us by binding to our cells. "The spike protein on the surface of the virus that gives it that function," Brown explained. "The spike protein on SARS-CoV-2 binds to the ACE2 receptors on our cells, fuses with our cells, gets in, and starts the infection."

What makes XBB 1.5 unique are several mutations on its spike protein. The mutation, according to scientists, helps the virus better latch onto human cells, and evade our immune defences.

This feature also makes XBB 1.5 far more transmissible than other subvariants.

"What we've seen is a lot of changes in the spike protein. It's less likely to be detected by existing antibodies from our vaccines and infections because it's changed in the part of the virus that actually sticks to our cells," said Brown.

"XBB1.5 has a lot of changes that increase its ability to avoid the antibodies and to get into our cells."

So, the new jab isn't a booster?

Technically, no.

Public health officials are calling the updated formulation a vaccine, and not a booster, adding that the new jab is more similar to an annual flu shot.

"I think we wanted to emphasize this is an updated COVID-19 vaccine, and similarly, we update influenza vaccines as well," Tam said during the briefing.

When can you get the shot?

During the briefing, Tam said Canadians can expect to receive the new shots at the beginning of October, adding public health officials are recommending "people to get protected both with COVID-19 vaccine and the flu shot."

This echoes NACI's guidance, which recommends a dose of the new formulation of the vaccine for people in the authorized age groups if it's been at least six months since receiving their last dose.

"The thing about respiratory viruses is that getting vaccinated is a team sport,"said Dr. Greer.

"When you choose to get vaccinated, you're also making a decision about how your decision affects other people."

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