New Data Suggests Canada’s ‘Bet’ To Delay, Mix, And Match COVID-19 Vaccines Paid Off

This is an excerpt from Second Opinion, a weekly summary of health and medical science news emailed to subscribers every Saturday morning. If you haven’t subscribed yet, you can do so by clicking here.

New Canadian data suggests that the bold strategy of delaying and mixing second doses of COVID-19 vaccines led to strong protection against infection, hospitalization and death, including 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 National Institute of Public Health of Quebec (INSPQ) show the decision to vaccinate more Canadians sooner by delaying seconds shots up to four months saved lives.

Researchers excluded long-term care residents, who are generally at increased risk of hospitalization and death from COVID-19, from the data to get a better idea of ​​the vaccine’s effectiveness in the general population, and the results were exceptional.

the analysis of nearly 250,000 people in British Columbia from May 30 to September 11 found that two doses of any of the three COVID-19 vaccines available in Canada were close to 95 percent effective against hospitalization, regardless of the approved vaccination combination.

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

dr danuta skowronski
Dr. Danuta Skowronski of the BC Center for Disease Control laid the groundwork for the decision to withhold the second doses and says the first data on the effectiveness of the vaccine is extremely encouraging. (Harman / CBC)

Dr. Danuta Skowronski, an expert in vaccine effectiveness and epidemiology leader at the BCCDC whose research sat down the foundations for the decision to withhold second doses based on the “fundamental principles of vaccination,” he says the first data is extremely encouraging.

“We were very happy to see during the period in which the delta variant was not only circulating, but predominated, that we had such high protection, nonetheless, against both infection and hospitalization,” the lead researcher of the analysis told CBC News.

“The protection was even stronger when the interval between the first and second doses was more than six weeks.”

In fact, research showed that the protection against COVID-19 infection from two doses of the Pfizer vaccine increased dramatically when the first and second doses were extended, from 82 percent after three to 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 less than for recipients of the mRNA vaccine, but they had comparable protection against hospitalization and that is the main goal,” he said.

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

While the work is still being finalized and has not yet been submitted as a preprint or peer-reviewed, the researchers felt it is important to get their first data now to inform the public and policy makers here and in the foreigner on the positive results.

“The mix and match schedules are protecting well, and my preference would be for those countries that don’t recognize that to be able to see our data as soon as possible,” he said, adding that the findings were sent to US officials for review. international travel policies.

“My hope is that when they see the evidence that those policies will change, that they are frankly inconsistent with the science.”

vaccine effectiveness graphic

Quebec data supports BC’s findings

In Quebec, thousands of miles away and with a different population, demographic composition, and early vaccine implementation approach: the results of a twin study to be published alongside the BC data were strikingly similar.

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

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

“The bottom line is whatever vaccine people have received, if they received two doses they should consider that they are very well protected against severe COVID-19,” said Dr. Gaston De Serres, epidemiologist at INSPQ. “That is the main message.”

The analysis found that the Pfizer and Moderna vaccines were 90 percent effective in preventing COVID-19 infections, whether asymptomatic, symptomatic, or those needing hospital care, a protection rate equal to those with a combination of AstraZeneca vaccine and MRNA.

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 (82 percent).

covid bc vaccinations 20210401
The research showed that the protection against COVID-19 infection from two doses of the Pfizer vaccine increased dramatically when the first and second doses were extended. (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 the hospitalization.

“For now, stay there. If there is a recommendation for you to get an additional dose of RNA, you will find out in time,” De Serres said. “But feel that what you have is still a very good regimen to protect you against what we fear the most, which is severe COVID-19.”

vaccine effectiveness graphic

The NACI recommendation In March, delaying the second dose of the three COVID-19 vaccines for up to four months was not without controversy at the time, and it certainly created confusion among many Canadians about whether they were adequately protected.

Canada’s chief scientific adviser Mona Nemer said in early March that the strategy amounted to “population-level experiment, “while at the same time health officials tried to reassure the public that the approach was safe and effective.

Deepta Bhattacharya, a University of Arizona immunologist who was not involved in the study, says the results are “very encouraging” and provide evidence of “improved protection in the real world” by delaying second doses.

But he admits that even he was initially skeptical.

“I was uneasy about it in large part because I wasn’t sure how well the protection would hold up in the meantime,” he said. “Obviously it turned out well … but it was risky, and that gamble paid off.”

Bhattacharya says that Canadian data now provides real-world evidence that vaccinated people produce more antibodies if their second injection is delayed, and the quality of those antibodies may actually improve, which could explain the better protection against delta.

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

vaccine effectiveness graphic

Keeping an eye on the prize means avoiding hospitalization

The data also has implications for whether average Canadians need booster injections, particularly given that emerging real-world data in other countries such as the U.S, Israel and Qatar show evidence of diminished immunity that has prompted the launch of third doses.

But experts warn that while countries that report lower vaccine effectiveness against COVID-19 infection may be making headlines, the biggest factor is that studies largely show that vaccines have long-term protection against severe COVID-19, which means hospitalization and death.

“We really should keep our eyes on the prize, which preserves the capacity of the healthcare system and prevents unnecessary suffering,” Skowronski said. “We are not going to prevent all cases of COVID-19. Our goal was never to prevent colds. Our goal was to prevent serious outcomes.”

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

“We have to be confident that the effectiveness of our vaccine 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 Vaccination and Vaccination. and the Saskatoon Infectious Diseases Organization which was not involved in the investigation.

“We should continue to implement public health measures and hope that at some point we will need a boost, but data like this will inform us when we do it and at this point it suggests that we do not need it yet, but we have.” to stay alert. ”

SEE | Canada recommends COVID-19 booster shots for long-term care residents:

covid boosters naci birak 280921.jpg?crop=1

NACI Recommends COVID-19 Booster Vaccines for Seniors in Long-Term Care

Amid a global debate over COVID-19 boosters, the National Immunization Advisory Committee recommends third doses for Canada’s most vulnerable, especially older people in long-term care homes. 1:58

Skowronski says that while he supports providing long-term care residents and immunosuppressed individuals with third doses of COVID-19 vaccines to increase their protection based on emerging data, even of Canada, there is still not enough evidence for average Canadians.

Until then, he says Canadians should feel well protected against severe COVID-19 outcomes in the delta-driven fourth wave if they are fully vaccinated with any of the Canadian-approved vaccine combinations.

“We will have to learn to live with SARS-CoV-2, even in its many future versions,” he said.

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

Leave a Comment