More and more Canadians get partial protection from one dose, and the proportion of full protection in two doses is half of the original. At a critical moment, this helped to promote our third wave in most parts of the country.

But some experts say that due to increased vaccine supply, declining COVID-19 levels, and the increasing threat of more contagious variants of the coronavirus, it’s time to switch to a second dose of priority for Canadians, which may jeopardize the progress made. .

“For Canada as a whole, from a life-saving perspective, there is no doubt that giving people a single dose and having them postpone the second dose is the best idea,” Allison McGill, Medical Microbiology and Infectious Diseases Said the doctor. Disease specialist at Mount Sinai Hospital in Toronto.

“Of course, I want two doses of the vaccine. But if the price of this vaccine might kill you because of it, that’s not right-it won’t work. I think we can all see this.”

This National Advisory Committee on Immunization (NACI) Based on the limited real-world evidence and the reality of the Canadian vaccine supply, an unparalleled recommendation was made to postpone the second dose for all Canadians in March by up to four months.

It said that if the second dose is extended nationwide by up to four months, by the end of June, nearly 80% of Canadians over the age of 16 will receive at least one dose.

This decision is not without critics, who pointed out that vaccine manufacturers recommend sticking to the approved three-week clinical trial of Pfizer-BioNTech and Moderna drugs and the four-week clinical trial of Oxford-AstraZeneca injections.

At the time, Mona Nemer, Canada’s chief scientific adviser, stated that the decision to postpone the dose amounted to “Population level experiment. “

The discovery of Dr. Danuta Skowronski, head of epidemiology at the British Columbia Centers for Disease Control (BCCDC), also determined the decision. One dose of vaccine is actually more effective Better than the clinical trials initially showed.

She told CBC News: “This is a planned welfare risk.” “This is the job of the public health department. This is our expectation of the public health department: to take emerging evidence in emerging crises, and Consider what is most beneficial to the people they serve.”

Skowronski said that there is no reason to suspect that the delay of the second COVID-19 vaccine will allow more time to generate an enhanced antibody response and improve the boost response of the second injection-just like other vaccines.

Xinxing research seems to prove her rights.

Studies have shown that delaying the second dose is the “right move”

A new Canadian preprint studyExperts who have not yet been peer-reviewed found that the effectiveness of the Pfizer-BioNTech and Moderna vaccines increased from 14% to 48% after the first injection to 71% after 35 to 41 days.

Observational studies surveyed nearly 325,000 people in Ontario from mid-December to mid-April and concluded that although the vaccine is less effective for people 70 years of age and older, after 28 days , Its vaccination rate has reached the level of young people.

Dr. Jeff Kwong, an epidemiologist and senior scientist at ICES, a research organization based in Toronto, said: “I think this is an important discovery. We only need to wait patiently after the first dose. The effect of the first dose is actually equivalent. it is good.” .

“This gives a great assurance that the strategy of getting as many people as possible to get the first dose is the right move.”

The latest research in the medical journal “The Lancet” Between December and February, researchers surveyed more than 23,000 vaccinated medical staff in the UK and found that the Pfizer-BioNTech vaccine can effectively prevent the incidence of COVID-19 at least 70% three weeks after the initial vaccination. .

Another study of the Lancet During the same period, a survey of 1.3 million people in Scotland was conducted and it was found that within 4 to 5 weeks after the first medication, Pfizer’s vaccination effectively prevented hospitalization rates exceeding 90% due to the use of COVID-19.

The study also analyzed the AstraZeneca-Oxford vaccine in the same population and found that the vaccine can effectively reduce the number of COVID-19 hospitalizations by 88%.

Skowronski said it’s not surprising that studies have shown that a single dose can provide “substantial protection,” which she believes is More than 90% In a letter published in a letter New England Journal of Medicine.

It’s time to modify the strategy

But now she thinks it’s time to modify the strategy.

She said: “A second dose is needed, one of the reasons is to increase the cross-coverage of other cyclic mutations.”

“Now that we have a vaccine supply, and now we have provided the first dose of vaccine especially among those high-risk priority groups, I think it is a good idea to provide the second dose now.”

Variants may spread behind the scenes in Canada

The provinces initially followed NACI’s guidance, but recently reduced the time between two shootings to As low as two months As the supply increases.

NACI released new recommendations It was said on Friday that the second dose should now be provided “as soon as possible”, with priority given to Canadians “before or when combined with other qualified populations, who have “the highest risk of serious illness and death due to COVID-19.”

Although the NACI guidelines do not specifically mention the threat of variants, experts say that the first variant B1617 discovered in India may pose a major threat to Canada’s future vaccine effectiveness.

Professor Ashleigh Tuite, an infectious disease epidemiologist and assistant professor at the University of Toronto’s Dalarana School of Public Health, said that B1617 may be spreading behind the scenes in Canada-just like the variant first discovered in the UK.

Watch | Provinces shortened the timetable for the second COVID-19 vaccination:

Some provinces have announced plans to shorten the timetable for the second COVID-19 vaccination as the supply increases. 1:59

She said: “We know that it is here, we know that we are importing cases, and we are in a situation where the total number of cases has dropped overall, but we are beginning to see signs that B117 is beginning to dominate.” “We are starting to see signs now. Is similar [with B1617]. “

But unlike B117, Tuite said that Canada cannot easily screen for B1617 through gene sequencing, so except for the classification as “unknown.”

Maria Sundaram, an infectious disease epidemiologist and postdoctoral researcher at the Center for Vaccine Preventable Diseases at the University of Toronto, co-authored the Ontario vaccine efficacy study. He said that Canada is fortunate that B1617 is in our study. Not playing a “main role” has not yet become popular, but this is something we “need to continue to pay attention to.”

Watch | Variants found in India related to the resurgence of COVID-19 in the UK:

The recovery of COVID-19 in the UK is related to the B1617 strain that was first discovered in India, which has raised concerns that it may delay its plans to come out of the lockdown. 1:56

B1617 is currently the main strain Set off the third wave in the UKNot only has it caused a surge in COVID-19 cases, it has also led to a surge in the number of hospitalizations, causing the country Speed ??up the vaccination plan To avoid jeopardizing the reopening of the British economy.

recent COVID-19 cluster in Newfoundland and Labrador Has grown to at least 60 cases and has been confirmed as Is caused by B1617, While in British Columbia, Quebec, Alberta and Ontario.

Dr. Michael Warner, Director of Intensive Care Medicine at Michael Gallen Hospital in Toronto, said that if Canada does not follow up, we may see more breakthrough infections in some vaccinated places, and may recur COVID-19 again.

He said: “We need to put people at the highest risk of exposure to COVID and the highest risk of serious illness from COVID, with their greatest protection.” “And I think we have enough supplies to do this without cannibalizing others. The first chance for everyone.”

McGill said that the fact that B1617 did not dominate in the UK until March means that Canada still has precious time to protect our most vulnerable people with our vaccine-if we act quickly.

“We may have a few months [B1617] This is an important question. . . . This means that we have a few months to give everyone a second dose, and we should be able to do this with ease. ”

“But part of me is still worried about what this virus can do.”

This is an excerpt from the “Second Opinion”, which is an excerpt sent to health and medical science news via email every week Subscribers every Saturday morning.If you haven’t subscribed yet, you can click Here.