Why giving COVID-19 booster shots to everyone in Canada is hard to justify

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Emerging research from around the world has sparked new fears about the declining protection COVID-19 vaccines provide over time against infection from the highly contagious delta variant, prompting some countries to move aggressively toward booster shots.

But the research these decisions are based on isn't definitive, and CBC News spoke to several Canadian and international experts who raised concerns with the controversial move to roll out third doses widely before more data is available and while much of the world remains unvaccinated.

"We're planning to hand out extra life-jackets to people who already have life-jackets, while we're leaving other people to drown without a single life-jacket," Dr. Mike Ryan, the World Health Organization's top emergencies expert, said during a news conference Wednesday.

The WHO has recently called for a moratorium on boosters until at least the end of September. But despite the concerns raised by health officials and other experts, countries are forging ahead with plans for additional doses now â€" including parts of Canada.

WATCH | WHO calls for temporary pause on COVID-19 booster shots:

WHO calls for temporary halt on COVID-19 vaccine booster shots4 days agoSaying the priority should be on immunizing health-care workers in low- and middle-income countries, WHO director general Tedros Adhanom Ghebreyesus called for a temporary moratorium on COVID-19 vaccine boosters. 1:44 Rapid shift to boosters worldwide

Israel extended booster shots to everyone over 40 on Friday, while France, Germany and the U.K. have announced third doses only for vulnerable populations at heightened risk of declining COVID-19 immunity.

The U.S. went a massive step further this week by announcing third doses for all Americans beginning next month, to bolster immunity against the much more contagious delta variant amid early signs the effectiveness of the vaccines could be dropping.

Several Canadian provinces have also made the decision to break away from the pack and pre-empt upcoming guidance from the National Advisory Committee on Immunization (NACI) on when booster shots may be needed and for whom.

Ontario will offer third doses to vulnerable populations, such as those in long-term care, First Nations elder care lodges and "higher risk" retirement homes, as well as for transplant recipients, certain cancer patients and other immunocompromised individuals.

Saskatchewan and Quebec previously announced plans to offer additional doses of mRNA vaccines â€" not because of waning immunity or the threat of delta, but for people who want to travel to countries that may not recognize mixed-vaccination status.

The tides have shifted rapidly on this issue over the past week and many Canadians may now be left wondering whether they'll need an additional shot â€" and when they'll get it.

WATCH | Ontario to offer 3rd COVID-19 shot to vulnerable groups:

Ontario to offer 3rd COVID-19 vaccine doses to vulnerable populations5 days agoThe Ontario government has announced it will offer third doses of COVID-19 vaccines to the most vulnerable, including transplant patients and people in long-term care, but experts say there’s not yet evidence they’re needed in the wider population. 1:59 Vaccine effectiveness data 'all over the place'

What prompted the sudden shift in favour of widespread booster shots?

The answer is largely based on conflicting emerging data from highly vaccinated countries around the world that signal a potential drop in immune protection in the population over time amid surges in cases driven by the delta variant.

But the data is anything but clearcut.

"The vaccine effectiveness data that we're 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 this, in part because all of these things are being estimated outside of the context of a clinical trial where you have a lot of control.… Now it's a mess." 

In a country where delta is the dominant strain, Israel's Ministry of Health released data late last month that implied two doses of the Pfizer-BioNTech vaccine was just 39 per cent effective against COVID-19 infection, a drop from 95 per cent seen in clinical trials and 64 per cent in real-world data earlier this year. 

Israeli Prime Minister Naftali Bennett receives a booster shot of COVID-19 vaccine at Meir Medical Center in the central Israeli city of Kfar Saba, on Aug. 20, after the country began administering them to people aged 40 and over amid a spike in infections. (Jack Guez/AFP/Getty Images)

But experts have raised concerns about the quality of Israel's data, suggesting it should be taken with caution before being used to justify the widespread use of boosters. 

"Much of the Israel data can be explained by the fact that with delta waltzing onto the scene, those who have been vaccinated longest are also those more likely to experience severe illness than others â€" in other words, the elderly," said Bill Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health.

"It is confusing because in some analyses, age is corrected for, but in others, not all." 

While it is reasonable to expect there is some waning protection from vaccines, especially with the spread of delta, Hanage said it's not to the extent that's being "bandied about" from the Israeli data and isn't necessarily seen in younger age groups. 

Dvir Aran, a biomedical data scientist at Technion â€" Israel Institute of Technology in Haifa, told CBC News he's "very skeptical" about the Israel estimates.

"The vaccine effectiveness that was calculated by the Israeli Ministry of Health is from a mix of early and late vaccinated individuals," he said, pointing to a lack of adjustment for confounders, or other factors, in the data. "So it's not clear what it even means."

Because of the different vaccines, rollout strategies and populations in each country, Hanage said it's reasonable to suspect the Israel data is skewed â€" especially because one would expect to see the dramatic results replicated elsewhere. 

"If you are relying on them as the grounds for a huge decision like boosters, that's not as strong a foundation as you'd like."

WATCH | Official explains why 3rd booster shot is being recommended in the U.S.:

U.S. NIH director explains why it's recommending a third booster shot4 days agoIn an exclusive interview, U.S. National Institutes of Health Director, Dr. Francis Collins tells Power & Politics a third vaccine dose is needed to help fight the spike in delta variant cases in the U.S. 5:06 Conflicting research raises more questions

Israel's vaccine effectiveness estimates are also significantly lower than research released in May from the U.K., which found they were 88 per cent effective against symptomatic disease from delta. 

A similar study from Scotland published in The Lancet medical journal in June also found the Pfizer-BioNTech vaccine was still 79 per cent effective. 

And Canadian researchers released data last month that found two doses of the Pfizer-BioNTech vaccine were 87 per cent effective against delta, similar to that of the alpha variant, at 89 per cent, and the beta variant, at 84 per cent.

Adding to the confusion, the U.S. Centers for Disease Control and Prevention (CDC) published three new studies this week that were used by federal officials as justification for mRNA boosters for all Americans in the weeks ahead. 

One study analyzed thousands of nursing homes across the U.S. between March and August â€" covering a time frame both before delta emerged and when it became a dominant strain â€" and found vaccine effectiveness at preventing infections dropped from 75 to 53 per cent.

Another study focused on New York state between early May and late July, as delta rose to more than three-quarters of new cases, finding a decline in vaccine effectiveness from  91 per cent to 79 per cent. 

A third CDC-published study looked at severity of disease across the U.S., a key figure missing from other research, and found mRNA vaccines were overall 90 per cent effective at preventing hospitalizations â€" and only slightly lower in the immunocompromised.

What approach should Canada take with boosters?  

Given the conflicting, contradictory and outright confusing nature of the emerging data on vaccine effectiveness in the past few weeks, the question remains: What Canada should do when it comes to boosters in the midst of a fourth, delta-driven wave? 

Canadian researchers at the University Health Network (UHN) in Toronto recently published a correspondence in the New England Journal of Medicine that showed evidence of "significantly higher immunogenicity" in transplant patients after a third dose. 

And a recent preprint study from UHN analyzed 119 Ontario long-term care residents and 78 staff over four months, finding much lower levels of neutralizing antibodies in the elderly patients â€" suggesting a possible need for a third dose in that group as well.

WATCH | Why this doctor says it's too soon to talk boosters:

Doctors says it's too soon to talk about booster shots2 days agoInfectious diseases physician Dr. Isaac Bogoch, tells Power & Politics, it's too premature to talk about providing vaccine booster shots for the general population. 3:26

"It's very clear that older adults, and in particular frail older adults, don't mount the same immune response that younger adults do," said Dr. Allison McGeer, a lead study author and a medical microbiologist and infectious disease specialist at Mount Sinai Hospital.

"And while that's not unexpected, it does raise the issue of whether those levels are now low enough to reduce vaccine efficacy."

Given that research, and the smorgasbord of other data from around the world, Ontario's move to offer third doses to older, vulnerable groups makes sense for the rest of Canada. 

But experts say we shouldn't extend boosters to the general public just yet.

"It becomes a slippery slope," said Dr. Zain Chagla, an infectious diseases physician at St. Joseph's Healthcare Hamilton and an associate professor at McMaster University. 

"For sure, in the immunocompromised, long-term care residents and elderly, the stakes are high enough this is good to accept. But for regular, healthy folks â€" is this really going to lead to gains, or simply lower mild illnesses in otherwise healthy people, or nothing at all?"

A lab technician works at the Uganda Virus Research Institute on Dec. 18, 2020. The institute handles much of the country's COVID-19 testing and case numbers have recently spiked there with just over one per cent of the population vaccinated. (Lily Martin/CBC)

Bhattacharya says at the end of the day, we need to look at where a dose will make the most impact â€" especially as COVID-19 continues to ravage other countries with extremely low vaccine coverage.

"There is not a shred of doubt that the bang for the buck in getting an unvaccinated person vaccinated â€" wherever they are in the world â€" is far greater than giving someone a booster shot," he said

"Even within the wide range of possibilities as to how much a booster shot may help, it's definitely not going to be as beneficial as giving it to someone who's never had it. There's no question about that."

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