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In defence of Canada’s unprecedented decision for a four-month vaccine interval

Seniors across the country are rightly enraged that they were promised a 21-day interval between vaccine doses only to have that appointment pushed into July due to new recommendations by the National Advisory Committee on Immunization prescribing a four-month interval between doses. Seniors, after all, were the most vulnerable to COVID-19.

Throwing thousands of Canadian seniors into three extra months of vaccine limbo was never going to be popular, particularly when Canada is the only jurisdiction on Earth to use a four-month interval between doses.

That controversy is not going to abate anytime soon, but below find the best arguments as to why Canada’s decision to stretch its booster shot gap could end up saving lives.

In a pandemic that has been defined by near-constant government missteps, this may be one of the few times where Canada has prioritized science over political expediency.

Death rates across Canada are plummeting

As you read this, Canada has a lower rate of deaths from COVID-19 than Israel. That’s right; if you live in a country with near-blanket vaccination coverage, you are more likely to die of COVID-19 than in a country with a lower vaccination rate than Poland. After spiking in January, Canadian deaths from COVID-19 have been in freefall for two months.

At the same time, our case rate is through the roof, with skyrocketing case numbers in British Columbia, Ontario and elsewhere. These rising case numbers are being attributed to the more contagious and more fatal variants of concern, which are now affecting younger, populations more severely. But they do not seem to be translating into fatalities at the rate they once did earlier in the pandemic. Whatever criticisms can be levelled against Canada’s vaccination strategy, it seems to be yielding results in the one metric that matters most.

Getting just one dose of the Pfizer vaccine doesn’t provide the 95 per cent risk reduction of the completed two-dose regime, of course, but that first shot is turning out to be surprisingly potent. Even among patients that are 70 years or older, U.K. data is showing that just the first shot can lead to an 85 per cent decrease in deaths.

The 21-day gap between doses was always somewhat arbitrary

There is no spreadsheet at Pfizer headquarters saying that 21 days is the optimum, experiment-tested gap to maximize the effectiveness of their vaccine. In fact, it’s a number largely pulled out of thin air.

“I know this sounds crazy, but it’s arbitrary. If you look for literature that documents why that’s the best time point, there isn’t any,” David Topham, a University of Rochester immunologist, said in a February interview.

In fact, the typical rule of thumb is that booster shots have the best potency when administered at least two months after the initial dose.

Vaccinations for HPV, Hepatitis A and Hepatitis B, among others, all have their boosters at five months or more. Boosters shots for avian flu, meanwhile, have been found to be more effective at six months than if given only 28 days after the first shot, according to a 2009 study.

The main reason Pfizer went with a three-week interval was because it was the shortest reasonable timeline for a two-dose vaccine.

“You just pick a dosing interval,” Paul Offit, a member of an FDA vaccine advisory panel, told Science magazine in December.

All this is to say that while Pfizer has been careful to recommend a 21-day interval between doses, it’s a number that has about as much science behind it as the expiry date on a jar of mustard.

It’s why, in both the U.K. and the U.S., vaccine advisory panels have had few qualms about extending the interval.

If you want the pandemic squashed, you want quantity over thoroughness

The optimum way out of this pandemic for Canada, of course, would be to do like the Americans or the Brits and secure a bottomless supply of vaccines. But we didn’t: Canada is in 41st place in the global race for vaccination coverage.

Right now, every Canadian receiving their second shot represents a Canadian who couldn’t get their first shot.

And with most provinces still vaccinating their high-risk populations, at this stage, that “second Canadian” is still likely to be an 80-year-old with mobility issues or a 65-year-old with diabetes.

Policymakers were thus at an impasse: How to squash this pandemic as quickly as possible with only a very limited supply of vaccines.

And with a shot whose effects are far more dramatic as a first dose than as a booster, the raw calculus was easy.

As the particularly dramatic words of a commentary in the New England Journal of Medicine put it, “given the current vaccine shortage, postponement of the second dose is a matter of national security that, if ignored, will certainly result in thousands of COVID-19–related hospitalizations and deaths … that would have been prevented with a first dose of vaccine.”

Source: Tristin Hopper – NATIONAL POST