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Emerging research from around the world has raised new concerns about the reduced protection that COVID-19 vaccines provide over time against infection from the highly contagious delta variant, prompting some countries to move aggressively toward booster vaccines.
But the research that these decisions were based on isn’t definitive, and CBC News has spoken to several Canadian and international experts who have raised concerns about the controversial move to introduce third-dose doses on a large scale before more data is available and while much of the world remains vulnerable.
“We plan to distribute additional life jackets to people who already have life jackets, while letting others drown without a single life jacket,” Dr. Mike Ryan, WHO’s chief emergencies expert, said during a press conference Wednesday.
WHO recently called to stop the reinforcement Until the end of September at least. But despite concerns raised by health officials and other experts, countries are moving forward with plans for additional doses now — including in parts of Canada.
Watch | WHO calls for pause on COVID-19 booster shots:
Quick switch to reinforcements around the world
Israel extended booster shots to anyone over the age of 40 Friday when France, Germany and the United Kingdom They announced third doses only to vulnerable populations at increased risk of reduced immunity to COVID-19.
The United States took a big step forward this week Announcing the third dose for all Americans early next month, to boost immunity against the most contagious delta variant amid early signs that the efficacy of vaccines could decline.
Several Canadian provinces have also made the decision to stay away from the pack and anticipate upcoming guidance from the National Immunization Advisory Committee (NACI) about when and to whom booster shots may be needed.
Ontario will Third doses are given to vulnerable populations, such as those in long-term care, First Nations nursing homes and “high-risk” retirement homes, as well as for transplant recipients, some cancer patients, and other immunocompromised individuals.
Saskatchewan And Quebec He announced earlier plans to offer additional doses of mRNA vaccines — not because of weak immunity or the Delta threat, but for people who want to travel to countries that may not recognize a mixed vaccination status.
The tides have turned quickly on this issue over the past week, and many Canadians may now be left wondering if they’ll need an extra shot — and when they’ll get it.
Watch | Ontario presents its third COVID-19 snapshot for vulnerable groups:
Vaccine efficacy data ‘everywhere’
What prompted the sudden shift in favor of boosted shots at scale?
The answer is based largely on conflicting emerging data from highly vaccinated countries worldwide that suggest a potential decrease in population immune protection over time amid sudden increases in cases driven by the delta variant.
But the data is not entirely clear.
“The vaccine efficacy data we are getting are all over the place,” said Deepta Bhattacharya, an immunologist at the University of Arizona.
“It’s really hard to know what to make of all of this, in part because all of these things are valued outside the context of a clinical trial where you have a great deal of control … Now it’s a mess.”
In a country where Delta is the dominant strain, the Israeli Ministry of Health released data late last month indicating that two doses of the Pfizer-BioNTech vaccine were just 39 percent Effective against COVID-19 infection, a drop of 95 percent seen in clinical trials and 64 percent In real world data earlier this year.
But experts have raised concerns about the quality of the Israeli data, noting that it should be taken with caution before it is used to justify the widespread use of boosters.
“A lot of the Israeli data can be explained by the fact that as the dancing delta comes onto the scene, those who have been vaccinated for longer are also more likely to develop severe disease than others — in other words, the elderly,” said Bill Hanage, an epidemiologist at Harvard TH Chan School of Public Health.
“It’s confusing because in some analyses, age is corrected, but in others, it’s not all.”
While it is reasonable to expect there some Vaccine protection wanes, especially as Delta spreads, Hanage said not to the extent that it is “covered up” from Israeli data and isn’t necessarily seen in younger age groups.
Dvir Aran, a biomedical data scientist at the Technion-Israel Institute of Technology in Haifa, told CBC News that he was “extremely skeptical” about the Israeli estimates.
“The vaccine efficacy calculated by the Israeli Ministry of Health is from a combination of early and late vaccination,” he said, noting that confounding data or other factors were not adjusted for. “So it’s not clear what it even means.”
Given that each country’s vaccines, deployment strategies, and populations differ, Hanage said it’s reasonable to suspect the Israeli data is skewed — especially since one would expect to see the dramatic results replicated elsewhere.
“If you’re relying on it as the basis for a huge decision like reinforcers, it’s not as strong a foundation as you’d like.”
Watch | The official explains why the third booster shot is recommended in the US:
The conflicting research raises more questions
Vaccine efficacy estimates in Israel are also significantly lower than research released in May from the United Kingdom, which found that it is 88 percent effective Against symptomatic disease of delta.
A similar study from Scotland published in the medical journal The Lancet in June found that the Pfizer-BioNTech vaccine still remains. 79 percent effective.
Canadian researchers released data last month finding two doses of the Pfizer-BioNTech vaccine 87% effective against delta, similar to the alpha variant, at 89 percent, and the beta variant, at 84 percent.
Adding to the confusion, the US Centers for Disease Control and Prevention (CDC) published three new studies this week that federal officials have used to justify mRNA boosters for all Americans in the coming weeks.
one study It analyzed thousands of nursing homes across the US between March and August — covering a time frame before the emergence of the Delta and when it became a dominant strain — and found that the vaccine’s effectiveness in preventing infection dropped from 75 to 53 percent.
Another study Focused on New York state between early May and late July, where deltas rose to more than three-quarters of new cases, and found a drop in vaccine efficacy from 91 percent to 79 percent.
A third study published by the Center for Disease Control It looked at disease severity across the United States, a key figure missing from other research, and found that mRNA vaccines were generally 90 percent effective at preventing hospitalizations — and only slightly less at weakening immunity.
What approach should Canada take with boosters?
Given the conflicting, contradictory, and utterly confusing nature of the data emerging about vaccine efficacy in the past few weeks, the question remains: What should Canada do when it comes to boosters in the midst of a Delta-driven fourth wave?
Canadian researchers at the University Health Network (UHN) in Toronto recently published a file Correspondence in the New England Journal of Medicine which showed evidence of ‘significantly higher immunity’ in transplant patients after a third dose.
A recent prepress study from UHN that analyzed 119 long-term care residents in Ontario and 78 employees over a four-month period, and found significantly lower levels of neutralizing antibodies in elderly patients — suggesting a third dose may be needed in that group as well.
Watch | Why this doctor says it’s too early to talk about reinforcers:
Dr. Allison McGuire, lead study author and a medical microbiologist and infectious disease specialist at Mount Sinai Hospital, said.
“And while this is not unexpected, it does raise the question of whether these levels are now low enough to reduce the efficacy of the vaccine.”
Given this research, and other datasets from around the world, Ontario’s move to introduce third doses to the older and vulnerable groups makes sense for the rest of Canada.
But experts say we shouldn’t be extending boosters to the general public just yet.
“It becomes a slippery slope,” said Dr. Zane Chagla, MD, an infectious disease physician at St. Joseph’s Healthcare in Hamilton and associate professor at McMaster University.
“Sure, for immunocompromised residents, long-term caregivers and the elderly, the risks are high enough, and that’s a good thing to accept. But for regular, healthy people – will this really yield gains, or simply reduce mild illness in The other cases are healthy people, or nothing at all?”
At the end of the day, Bhattacharya says, we need to consider where the dose will have the greatest impact — especially as COVID-19 continues to devastate other countries with very low vaccine coverage.
He said: “There is no doubt that the knockout blow to getting a vaccine to an unvaccinated person – wherever in the world – is much greater than giving someone a booster dose.”
“Even within the wide range of possibilities as to how useful a booster shot will be, it certainly wouldn’t be as useful as giving it to someone who hasn’t had it before. There’s no doubt about that.”