Thursday, November 24 2022

The timing of your next COVID-19 vaccine may be more important than ever, as highly contagious Omicron subvariants are on the rise in Canada and waning immunity from previous vaccination and infection threatens to fuel another surge.

Canada is once again a hotbed of variants, with BA.2.12.1 now accounting for over 40% of COVID cases, while BA.4 and BA.5 are rapidly gaining ground at over 10% combined at the end of May – a jump major compared to less than 1% weeks earlier.

But the latest federal data available there are weeks of delay and modeling experts at CBC News have estimated that the true proportion of BA.4 and BA.5 cases is over 20% – and could reach 50 – with one of them likely to become dominant in the coming weeks.

“COVID-19 has shown us over the past few years that there may be more surprises to come,” Canada’s Chief Public Health Officer, Dr. Theresa Tam, said during a briefing. Friday press conference.

“The virus is still circulating in Canada and internationally and factors such as viral evolution and waning immunity are expected to impact COVID-19 activity in the future.”

Preparing for a “potential resurgence”

Tam said Canada’s path forward with COVID will not be straightforward, and officials are bracing for a “potential resurgence” that could lead to “severe impacts” in the future as Omicron subvariants are fighting for dominance, and new variants may yet emerge.

“Omicron evolved and it’s so different from our pre-Omicron vaccines and infections – the kind of immunity you got is just a different beast,” said Sarah Otto, an expert in modeling and evolutionary biology at the University of British Columbia.

“And so what we see with vaccine protection is that it’s not so much the number of doses as the date of your last dose, and I think that’s because the neutralizing antibodies in our bloodstream , they don’t recognize the virus too.”

That’s why virologists and immunologists say it’s so important to plan our next vaccines before another potential wave or when new variants start surging in Canada, so that we aren’t caught rushing to deploy doses in the middle of a rapidly worsening wave – such as when Omicron first hit in December.

When should you receive a 4th dose?

Canadian National Advisory Committee on Immunization (NACI) highly recommended second boosters for people aged 80 and over and other vulnerable groups in April, but stopped short of recommending a fourth vaccine for all Canadians.

The reason for this decision may be down to timing, with updated vaccines on the horizon that may be more resistant to Omicron subvariants, and a quieter period of COVID activity in the summer buying us time before another vaccine deployment is needed.

But NACI guidelines also recommends that eligible people wait six months after their last dose for a second booster, adding that the timing “may need to be balanced with local and current epidemiology” and that “shorter intervals” may be needed if another wave occurs. struck.

“When we start to see BA.4 and BA.5 leading to an increase in cases, I think we should be nimble and expect to need to get the callbacks – but it’s that waiting game,” Otto said.

“The longer you wait to get the vaccine, the newer it is and the more powerful it is in the next wave. So you don’t want to get it months before the next wave – Canada should really push for vaccines. at the beginning of a wave.”

Otto said Canada will likely see another wave driven by BA.4 and BA.5, but how bad it gets and if it has already started is not yet clear, although some provinces like Ontario and British Columbia find a recent increase in COVID sewage monitoring.

Michelle Quick, 33, receives her second dose of the Pfizer-BioNTech COVID-19 vaccine during a one-day pop-up clinic at the Eaton Center mall in Toronto on July 27, 2021. (Evan Mitsui/CBC)

Updated vaccines may be insufficient

Virologists and immunologists also worry that repeated boosters with COVID-19 vaccines tailored to the original strain of the virus may no longer be sufficient, and that updated vaccines may be needed to mitigate another potential wave within months. coming.

Moderna’s bivalent vaccine is a strategy that many are pinning their hopes on, but experts fear that targeting the original Omicron strain may not be enough due to to research showing a lack of cross-protective immunity against the very different BA.2.12.1, BA.4 and BA.5.

This experimental vaccine combines Moderna’s original vaccine with protection against Omicron, and while preliminary data has shown to seem to work, it has not yet been tested in the real world against the other sub-variants.

WATCH | Moderna’s vaccine targeting Omicron shows promise:

Moderna’s ‘bivalent’ booster can offer good protection, expert says

Toronto pulmonologist Dr. Samir Gupta explains how Moderna’s planned new vaccine could provide broad protection against multiple mutations in the coronavirus. Moderna’s dual-variant booster is currently in testing.

“I don’t think we’re going to see any major benefit from boosting with an Omicron-specific booster than just regular boosting with the (original) strain,” Otto said.

“Anyway, the boost helps because it increases antibody levels, but I don’t think it increases them much more in a way that will help us neutralize Omicron.”

“We need better long-term strategies”

University of Toronto immunologist Jennifer Gommerman says Omicron-specific boosters may be effective against real-world Omicron subvariants, but only if the virus doesn’t throw something else at us within months. coming.

“If Omicron is basically all the tricks the virus has left behind, then of course I think it makes sense to do Omicron-based vaccinations because we now have a very different virus than we had at the start. of the pandemic,” she said. .

“The problem would be if the virus still had enough real estate to create a new version of itself that was really different from Omicron – so that wouldn’t be what we would want to take.”

Alyson Kelvin, a virologist at the Canadian Center for Vaccinology and the Vaccine and Infectious Disease Organization in Saskatoon, said whether or not a bivalent vaccine would protect against the Omicron subvariants currently circulating is a “huge question”.

“At this point, I think we should expect new variants, whether it’s a new sub-line of Omicron or a whole new variant,” she said.

“We need better long-term strategies and personally I don’t think a bivalent vaccine is, from what we’ve seen of the virus, a sustainable strategy. It’s about figuring out how we can cover more variations at a time to anticipate what the next variation is going to be.”

Gomerman said nasal boosterswhich are not yet available, will likely protect against infection better by targeting a different arm of the immune system – but while several are in development, including by a team of McMaster College, they could still be years away.

WATCH | McMaster University is developing nasal vaccines against COVID-19:

McMaster University is developing inhaled aerosol COVID-19 vaccines

Professor Fiona Smaill of McMaster University in Hamilton, Ont., is conducting trials for two new inhaled aerosol drugs intended to serve as COVID-19 booster vaccines.

New variants could alter the booster schedule

Canada must now decide whether the goal of its strategy with current-generation vaccines is to protect against severe COVID or to try to prevent transmission altogether, Gommerman says, until a new vaccine or a variant changes the game.

“If your goal is to prevent infection, we’ll just have to keep pacing forever,” Gommeman said. “But if the goal is to protect the vulnerable, then we’ve already done that.”

Gommerman said she would not receive a fourth dose unless she knew there was a compelling public health reason to do so – such as if COVID levels were rising, vulnerable groups were at risk and the delay aligned against decreased immunity to infection.

“But I know that my immune protection in the form of immune memory is going to keep me from going to the hospital,” she said. “It won’t necessarily prevent me from being home for a week, but it will prevent me from going to the hospital and that’s what vaccines were designed for.”

Otto said new variants will likely continue to emerge, given the “huge amount of diversity of the virus that is maintained globally” and the fact that Omicron emerged independently of other variants like Alpha, Beta and Delta.

“We’re already seeing this substantial evolutionary change in Omicron – and all I’m saying is don’t overlook the other strains that are still circulating around the world,” she said.

“We’re in a part of Whac-A-Mole, and we don’t know where the next mole is going to be.”


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