New data suggests that Canada’s gamble ‘on delay, mixing and matching of COVID-19 vaccines paid off

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New Canadian data suggest the bold strategy to delay and mix the second dose of COVID-19 vaccines led to strong protection against infection, hospitalization and death — even against the highly contagious delta variant — which could provide lessons for the world.

Preliminary data from researchers at the British Columbia Center for Disease Control (BCCDC) and the Quebec National Institute of Public Health (INSPQ) show the decision to vaccinate more Canadians before noon. delay of second shot with up to four months saved lives.

The researchers excluded long-term nurses from the data, who generally have an increased risk of hospitalization and death of COVID-19 to get a better sense of vaccine efficacy in the general population — and the results were outstanding.

That analysis of close to 250,000 people in BC from May 30 to September 11, two doses of one of the three available COVID-19 vaccines in Canada found close to 95 percent effective against hospitalization — regardless of approved vaccination combination.

This means that for every 100 unvaccinated people who are seriously ill in Canadian hospitals, 95 of them could have been prevented by receiving two doses of either AstraZeneca-Oxford, Pfizer-BioNTech and Moderna vaccines, or a combination of the three.

Dr. Danuta Skowronski of the BC Center for Disease Control laid the groundwork for the decision to withhold the second dose, saying the early data on the effectiveness of the vaccine are extremely encouraging. (Harman / CBC)

Dr. Danuta Skowronski, expert in vaccine efficacy and epidemiology at the BCCDC, whose research laid the groundwork for the decision to withhold the second dose on the basis of the “basic principles of vaccinology”, says the early data are extremely encouraging.

“We were very pleased to see in the period when the delta variant not only circulated but dominated that we nevertheless had such high protection against both infection and hospitalization,” the researcher says in the analysis to CBC News.

“The protection was even stronger as the interval between the first and second dose was more than six weeks apart.”

In fact, research showed that protection against COVID-19 infection from two doses of the Pfizer vaccine increased dramatically as the first and second shoots spread — from 82 percent after three or four weeks to 93 percent after four months.

“For those who received the AstraZeneca vaccine as their first dose, their protection against any infection was lower than for mRNA vaccine recipients, but they had a similar protection against hospitalization, and that is the main goal,” she said.

“But for those who received a first dose of AstraZeneca and a second dose as an mRNA vaccine, their protection was as good as those who had received two mRNA vaccines. So that’s also a really important finding from this analysis. “

While the work is still being completed and has not yet been submitted as a pre-print or peer review, the researchers found it important to get their early data out now to inform the public and decision makers here and abroad about the positive results.

“The mix-and-match forms protect well, and my preference would be for those countries that do not recognize it to see our data as soon as possible,” she said, adding that the results were sent to U.S. officials for review. of international travel policies.

“My hope is that when they see the evidence that they will change the policies that are frankly not in line with science.”

Quebec data backs up findings from BC

In Quebec, thousands of miles away and with a different population, demographic composition and early approach to vaccine rollout – results of a twin study that will be published along with the BC data was astonishingly similar.

Of the 181 people who died from COVID-19 from May 30 to September 11 in Quebec, only three were fully vaccinated. Researchers say that equates to a vaccine effectiveness against death of up to 97 percent based on a population analysis of nearly 1.3 million people.

Like BC data, Quebec research also showed more than 92 percent protection against hospitalizations – with Pfizer, Moderna or AstraZeneca vaccines – against all circulating coronavirus variants of concern in Canada at the time, including delta.

“Takeaway is no matter what vaccine people had, if they were given two doses, they should consider that they are very well protected against severe COVID-19,” said Dr. Gaston De Serres, an epidemiologist at INSPQ. “That’s the main message.”

The analysis found that Pfizer and Moderna vaccines were 90 percent effective in preventing COVID-19 infections — either asymptomatic, symptomatic, or those in need of hospital treatment — a protection rate similar to that of an AstraZeneca and mRNA vaccine. vaccine combination.

For people who received two doses of AstraZeneca, research suggests a slightly lower level of protection against infection – but one that is still remarkably high at 82 percent.

The research showed that protection against COVID-19 infection from two doses of the Pfizer vaccine increased dramatically as the first and second shoots spread. (Darryl Dyck / The Canadian Press)

De Serres says the National Advisory Committee on Immunization (NACI) and the Quebec Immunization Committee (CIQ) are looking at whether additional doses may be needed for that group, but says it is “not so urgent” given the strong protection against hospitalization.

“For now, just sit still. If there is a recommendation for you to get an extra dose of RNA, you will know in time,” De Serres said. “But feel that what you have is still a very good regime to protect you from what we fear most — which is serious COVID-19.”

NACI recommendation March to delay the second dose of all three COVID-19 vaccines by up to four months was not without controversy at the time, and no doubt led to confusion among many Canadians as to whether they were adequately protected.

Canada’s Chief Science Adviser Mona Nemer said in early March that the strategy was a “experiment at the population level, “while health officials simultaneously tried to reassure the public that the approach was safe and effective.

Deepta Bhattacharya, an immunologist at the University of Arizona who was not involved in the study, says the results are “very encouraging” and provide evidence of “improved real-world protection” against second-dose delay.

But he admits that even he was initially skeptical.

“I was worried about it largely because I was just not sure how well the protection would hold in the meantime,” he said. “Of course it turned out well … but it was risky and that game paid off.”

Bhattacharya says the Canadian data now provide real evidence that vaccinated people produce more antibodies if their second shot is delayed, and the quality of those antibodies can actually improve – which may explain the better protection against delta.

“What I’m really wondering now is whether the recommendations will change fundamentally on when we should get the second shot,” he said, referring to other countries around the world. “I wish I had got mine later now in hindsight.”

Keeping an ‘eye on the premium’ means avoiding hospitalization

The data also has implications for whether average Canadians need booster shots, especially given that new real data in other countries such as U.S, Israel and Qatar show signs of declining immunity that have prompted the rollout of third doses.

But experts warn that while countries reporting reduced vaccine efficacy against COVID-19 infection may make headlines, the more important factor is that studies largely show that vaccines have long-term protection against severe COVID-19, which means hospitalization and death.

“We should really keep an eye on the price, which preserves the capacity of the health system and prevents unnecessary suffering,” Skowronski said. “We are not going to prevent all cases of COVID-19. Our goal was never to prevent snus. Our goal was to prevent serious outcomes.”

Nevertheless, the BC and Quebec data showed “no evidence” of declining immunity in the general population four months after the second mRNA dose and strong protection against infection of more than 80 to 90 percent maintained. The analysis does not go beyond five months, but the researchers will continue to monitor the vaccine’s effectiveness.

“We should be assured that our vaccine efficacy from this calculation, from what I have seen, will be robust with its protection,” said Alyson Kelvin, assistant professor at Dalhousie University and virologist at the Canadian Center for Vaccinology and the Vaccine and Infectious disease organization in Saskatoon that was not involved in the research.

“We must continue to have public health measures in place and expect at some point that we may need a booster, but data like this will inform when we do, and right now it suggests that we do not need it yet. – but we have to be vigilant. ”

SE | Canada recommends COVID-19 booster shots for long-term care workers:

NACI recommends COVID-19 booster shots for the elderly in long-term care

Amid a global debate over COVID-19 vaccine enhancers, the National Advisory Committee on Immunization recommends third doses to Canada’s most vulnerable, especially the elderly in nursing homes. 1:58

Skowronski says that although she supports providing residents on long-term care and immunocompromised third-dose COVID-19 vaccines to increase their protection based on new data, including from Canada, there is not enough evidence yet for average Canadians.

Until then, she says Canadians should feel well protected from serious results from COVID-19 in the delta-powered fourth wave if they are fully vaccinated with any of the approved vaccine combinations in Canada.

“We’ll have to learn to live with SARS-CoV-2, including in it’s a lot of future iterations,” she said.

“But as long as we can prevent serious outcomes and maintain the capacity of the health care system, we can come to a kind of mutual understanding with this virus.”

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