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Recently, Canada’s National Advisory Committee on Immunization lowered the recommended age for a COVID-19 booster shot from 70 and up to 50 and up, with the same proviso that it be at least six months after the second dose. It said those ages 18 to 49 could be offered a booster based on their individual risk and the degree of COVID-19 spread in their area.
On Tuesday, Health Minister Christian Dubé said Quebec would extend eligibility to several new categories, including health-care workers. People age 60 and up are to be offered a booster as of January.
Offering a booster dose to a larger segment of the population is mainly motivated by the rising case numbers, the risk of new variants and the waning of immunity with time. While the vaccines still offer very good protection against COVID-19 infection, even after six months, the goal of booster shots is to maximize the immunity so that we can withstand the coming winter and prevent a particularly disastrous fifth wave.
While case counts are rising, hospitalizations are still low and things so far are relatively stable. But nobody can realistically predict how the next few months will play out, with the two big wild cards being how bad the flu season will be and what impact, if any, the omicron variant will have. Given that uncertainty, the decision to optimize everyone’s immune status is an obvious one.
The benefit of boosters is becoming more evident. A recent study in  looked at the degree to which a booster prevented infections in those 40 and older. Using a test-negative design, researchers found the odds of testing positive were 85-per-cent lower for those who got a booster compared to those who didn’t. This is largely consistent with a previous study in the  , which found a 93-per-cent reduction.
The growing evidence for boosters suggests that most people will probably need one, although clearly older individuals who are furthest away from their second dose benefit most. Still, it is possible that we will ultimately come to think of this vaccine series as a three-dose rather than a two-dose vaccine. The original studies used a two-dose schedule because, frankly, time was of the essence back in 2020. Extending the studies by six months to administer a third dose would have resulted in an unjustifiable delay in rolling out the vaccines and beginning to bring the pandemic under control. It seems likely that we will ultimately find that three doses is the more optimal strategy for providing better more longstanding immunity.
It would not be the first time that the schedule for a vaccine has changed. The measles vaccine used to  in the 1970s. While it did help reduce cases and mortality from the disease, a single dose only offers upward of 85-per-cent protection, while the  brings the protection up to essentially 100 per cent. The fact that a second dose of the measles vaccine was added to the vaccine schedule didn’t mean that the vaccine had failed. The addition of a second dose, in 1997, led to the  from Canada.
No doubt, many hoped that after two vaccine doses everything would go back to normal. But life is never that simple. Access to vaccines in many parts of the world is a problem, and we need to worry not just about ourselves, but also about getting doses to countries where supply is scarce. We also cannot let COVID-fatigue lead us into therapeutic nihilism. We shouldn’t see vaccines as binary, as either miracles or useless. They have been extremely effective at blunting the worst of the pandemic, and by tweaking our vaccine strategy we can make them even better. Sometimes plans change, not because they failed, but because there is always room for improvement.
