What protection to expect from updated COVID vaccines this fall

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Canada has just approved a COVID-19 vaccine update to target the first highly contagious variant of Omicron, with doses expected to begin rolling out within days. But what exactly can we expect from these new shots when they land in the real world?

The updated Moderna vaccine is a combination of two strains, also called a “bivalent” vaccine, that targets both the original virus and the Omicron BA.1 variant that emerged late last year and has leads the biggest wave of infection and hospitalization in the pandemic.

Although the new shot does not directly target the dominant Omicron BA.4 and BA.5 sub-variants, that the The United States approved an updated plan for this week, Pfizer submitted an application for approval by Health Canada for its BA.4-5 vaccine on Friday and Moderna is expected soon.

“The evidence we have so far shows that the bivalent vaccine with BA.1 provides good protection against BA.4 and BA.5,” Deputy Director of Public Health Dr. Howard Njoo said during a briefing. a technical briefing on Thursday.

“Certainly, as the situation evolves, we will have to look at the evidence and see what is happening with real-world effectiveness.”

But what an updated booster can do for you depends on how vulnerable your immune system is, if you’re one of the millions of Canadians who have recently been infected with COVID, and when you last received a vaccine.

Will updated vaccines stop the spread of COVID?

Infectious disease experts, virologists, epidemiologists and immunologists hope updated vaccines will be more effective at preventing transmission than original vaccines – at least initially – but also warn Canadians not to expect let them be a quick fix.

With limited data on the impact these vaccines will have, all eyes will be on what effect they will have on slowing infection and transmission rates and whether they better protect vulnerable groups of the population. as the fall and winter months approach.

“We don’t know what the impact is because it’s not available,” Chief Public Health Officer Dr. Theresa Tam said at a press conference Thursday when CBC News told her. asked how effective updated vaccines would be in stopping the spread of the virus.

Tam said she hopes Moderna’s new BA.1 targeted bivalent vaccine will boost protection against infection and transmission — at least until the fall.

Clinical trial data on BA.1 targeted vaccines from Modern and Pfizer-BioNTech suggests that they provide slightly stronger immune protection against Omicron than the original vaccines, but exactly what this translates to in the real world remains to be seen.

“The immune responses to these variant-matched boosters are modestly encouraging, but we are still awaiting definitive clinical evidence,” said Dr. David Naylor, who co-chairs the federal government’s COVID-19 Immunity Task Force.

“That said, even if their marginal benefits are small, they could have a significant positive impact if their novelty revives public interest to be stimulated.”

A new pre-publication modeling studywhich has not been peer-reviewed, suggested that updated vaccines may not be much more effective than existing boosters in a population with hybrid immunity to vaccination and infection, particularly with respect to relates to protection against serious illnesses.

But it could still lead to significant population-level protection, with the preprint also suggesting that for every 1,000 people vaccinated with an updated booster, an average of eight fewer people would be hospitalized compared to the original vaccines.

“We don’t yet know the extent of this improvement, but it will likely be quite limited,” said Dr. Gaston De Serres, an epidemiologist at the National Institute of Public Health of Quebec (INSPQ).

“Particularly against serious consequences such as hospitalization for which, until now, the original [vaccines] were quite successful. »

What can updated COVID vaccines do for you?

More than half of Canadians have been infected with COVID since the emergence of Omicron and its highly contagious subvariants, and the added protection against prior infection in a vaccinated population appears to provide an advantage.

A new research letter published in the New England Journal of Medicine examined the risk of infection with BA.5 among people in Portugal who had already been infected with past variants, including BA.1 and BA.2, and found that they had strong protection against the new variant.

This is partly because Portugal has such high levels of vaccination, with over 98% of the population studied receiving at least two doses, which means that, just like in Canada, our high levels of vaccination and Two doses of infection provide strong immune protection.

Two preprinted Canadian studies of May and Junewhich have not been peer-reviewed, also found that prior Omicron infections provided robust immunity against future reinfections and hospitalizations, especially when combined with vaccination.

“In general, one can predict that those who have hybrid immunity will be better protected,” said Dr. Danuta Skowronski, vaccine effectiveness expert and chief epidemiologist at the BC Center for Disease Control and co-author of the preprints.

“And it’s also true that vaccine strains that better match the circulating variant are likely to offer better protection.”

Also important to consider is the longer you wait after your last infection or vaccination, with emerging evidence suggesting that getting a booster shot too soon after being infected or vaccinated may impact vaccine effectiveness .

A new baby pre-publication studywhich has not been peer-reviewed, found that getting a booster within two months of an infection can negatively impact B cells that help generate immune protection against serious illnesses.

NACI recommends wait three months after an infection before getting another hit, and three to six months between doses, but also said in its most recent guidance that anyone at high risk for severe COVID in Canada should be offered a drop booster.

“Timing is everything and generally the recommendations are to wait a few months after infection before getting a booster dose,” Skowronski said.

She added that people shouldn’t immediately rush to get a booster after an infection because it could actually interfere with the immune response.

Updated vaccines will ‘help’, but not a ‘miracle’

Canada still has a “worrying gap” in third-dose coverage, Naylor said, with less than half of Canadians to have received a reminder even if it brings significant additional protection against severe COVID-19. Only about 12 percent received a fourth dose.

“As we start heading into the fall and almost certainly start to see cases increase again, the updated reminder will definitely be better than not getting a reminder at all,” said Deepta Bhattacharya, professor of immunobiology at the University of Arizona. .

“Since BA.5 is still circulating, I don’t really mind taking these boosters and they’ll probably work better than just another shot of the original.”

Bill Hanage, an epidemiologist at Harvard’s TH Chan School of Public Health in Boston, said it’s important to consider that even though the original vaccines were far from exactly identical to Omicron, they still offered strong protection against serious diseases.

“But tighter matches should now do more,” he said in an email. “In particular, there may well be a period after the shooting when people are immune to infection.

Bhattacharya said the “big question” on our minds right now is how effective updated vaccines will be at stopping transmission in the real world – and for how long.

“Are we starting to restore some of the protection against any infection or symptomatic infection with these reminders? I expect us to do that,” he said. “Exactly how long this effect will last, I think, remains to be determined.”

Dr Allison McGeer, a medical microbiologist and infectious disease specialist at Mount Sinai Hospital in Toronto, said the updated injections could give a slight boost to neutralizing antibodies that can prevent transmission – and that protection extra is “not nothing”.

“An additional dose of the original vaccine results in substantial increased protection against BA.4 and BA.5. It’s not perfect, but I think we’re finding that nothing is perfect,” she said. “Bivalent vaccines may be a little better, but it’s not going to work miracles.”

Bhattacharya said that although clinical trials showed there was only a two-fold increase in protective antibodies against the BA.1, BA.4 and BA.5 variants targeted by Moderna and Pfiizer in their bivalent vaccines, this is still an important protection.

“If you look at the data, that’s a ton more antibodies being made,” he said. “So I have every reason to expect them to help me – and probably a lot.”