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It's 'high time' that authorities revise definition of 'fully vaccinated': experts


As more evidence emerges on the efficacy of third doses of the COVID-19 vaccine, experts say it’s high time public health authorities revise the definition of “fully vaccinated” to include a booster dose.

While most SARS-CoV-2 vaccines available in Canada were initially developed and tested to include two doses – with the exception of the Johnson & Johnson vaccine – a primary course should instead consist of three doses, said Colin Furness, an expert in infectious disease epidemiology from the University of Toronto.

“Someone who's only had two shots will say, ‘I’m fully vaccinated,’ and that's what the authorities are saying, [but] the authorities have got it wrong,” Furness told in a telephone interview on June 1. “When we look at the diminishment of immunity after the second dose, really, this is a three-dose vaccine.”

A newly released meta-analysis conducted by the Chinese University of Hong Kong earlier this year assesses the efficacy of different vaccine combinations in protecting against COVID-19. Involving 53 studies that include more than 100 million people, the meta-analysis showed that three doses of an mRNA vaccine were highly effective in protecting against COVID-19 infection, whether symptomatic or asymptomatic, at 96 per cent.

Three doses of an mRNA vaccine also had a 95 per cent efficacy rate in reducing COVID-19-related hospitalization. The study concludes that three doses of a COVID-19 vaccine are necessary to protect against infection from the Omicron variant of the virus.

Despite this, the Public Health Agency of Canada’s (PHAC) definition of “fully vaccinated” with regards to COVID-19 vaccines continues to refer to those who have received a primary series of the vaccine. The primary series involves two doses of most vaccines approved for use in Canada (such as mRNA vaccines, as well as the AstraZeneca, Novavax and Medicago vaccines), or one dose of the Johnson & Johnson vaccine.

“As the epidemiological context of COVID-19 continues to evolve, the Government of Canada will continue to monitor the efficacy and effectiveness of vaccines being used in Canada and may provide further recommendations on the definition of a fully vaccinated person,” PHAC spokesperson Anna Maddison wrote in an email to on June 1.

It’s important to note that as the COVID-19 pandemic has progressed, the SARS-CoV-2 virus has evolved away from what vaccines were initially developed to target, Furness said. This viral evolution has led to a reduction in the efficacy of current vaccines, particularly when it comes to protecting against infection from Omicron, the newest variant of concern. Despite this, three doses of the vaccine continue to offer solid protection, particularly against severe outcomes of COVID-19 such as hospitalization and death, Furness said. As a result, he said he hopes to see a change in the definition of “fully vaccinated.”

“Hypothetically, if we had a vaccine that prevented long COVID, hospitalization and death, but didn't stop anybody from getting infected, I would call that wildly successful; we’d all get a cold … but no one would get really sick,” Furness said. “There's no question we don't have that, but three doses of a COVID-19 vaccine takes us closer to that.

“When we talk about ‘fully vaccinated,’ we should be talking about three [doses].”

In Canada, just over 20 million third and fourth doses of the COVID-19 vaccine have been administered so far, based on data compiled by According to PHAC, about 55.5 per cent of Canadians aged 12 and older are vaccinated with three doses of the COVID-19 vaccine, which translates to roughly 18.5 million people.


University of Saskatchewan epidemiologist Dr. Nazeem Muhajarine also advises those who are eligible for their third dose of the COVID-19 vaccine to go and get it. However, rather than tying the definition of “fully vaccinated” to a specific number of doses, he said public health authorities should focus on advising Canadians to keep their vaccination status “up-to-date” based on the latest recommendations from the National Advisory Committee on Immunization (NACI).

“’Fully vaccinated’ no longer works, in my mind, as a definition of being up-to-date on the vaccine doses that you need to get … I think it is high time that we [change] that,” he told on June 1 in a telephone interview. “It is about being caught up with all the vaccines that you're recommended to get at this stage of the pandemic.”

The World Health Organization’s current definition of a primary vaccination series refers to one or two doses of COVID-19 vaccines approved for emergency use, depending on the product. In the context of international travel, the government of Canada considers those with at least one dose of the Johnson & Johnson vaccine, or two doses of any of the remaining vaccines approved for use in Canada to be fully vaccinated. Provincial governments such as that of Ontario, however, have updated the wording in their latest guidance to suggest that people get vaccinated with, “all recommended COVID-19 vaccine doses, including any booster dose(s) when eligible.”

Additionally, provinces across Canada have now made third doses available to those aged 12 and older, and NACI strongly recommends third doses for all adults in Canada.

While Furness said he admits that COVID-19 vaccine protection may also wane following a third dose, he still recommends that those who are eligible to get their booster shot do so, given the additional protection it offers compared to just two doses.

“It may wane, but that would still really interrupt transmission and it would interrupt outbreaks, if we could get enough people [vaccinated] with a third dose,” he said.

A third dose of the COVID-19 vaccine will also help to further protect populations from new variants or sub-variants that may surface in the future, Muhajarine said.

“As long as we have multiple variants spreading, that opens the possibility for new variants to emerge – that is how the evolution of these variants happen,” he said. “I don't really see any evidence-based reason for keeping 'fully vaccinated' to only two primary doses.”

Uptake for the third dose of the COVID-19 vaccine has been slow in comparison to that of the first and second doses, said both Furness and Muhajarine. Part of the reason for this is that the vaccine was initially presented to the public as being comprised of two doses, making people think that was all they needed to be sufficiently protected, Furness said.

“That's the mental model that most people had,” he said. “So when we started to say you kind of need a third dose now … [they] said, ‘You sold us an idea that there was a two-dose vaccine and I signed on, now you're changing the deal and I don't like that, I'm walking away.’”

Contributing to this lack of enthusiasm towards getting boosted was the lifting of vaccine mandates by provincial governments across the country earlier this year, Muhajarine said. Those unable to enter restaurants or movie theatres because they were unvaccinated, for example, are no longer barred, with proof of vaccination no longer required.

“Vaccine mandates worked in terms of actually getting people who are eligible to get a second dose,” Muhajarine said. “But when governments started to pull back those public health measures and vaccine mandate measures, I think people really lost that incentive.”


While he does call on public health authorities to include third doses in the definition of “fully vaccinated,” Furness said it will take more than changing the definition to encourage people to actually get their booster shot. Part of the solution lies in vaccine mandates being implemented and enforced by employers and governments.

“[If] your employer has mandated vaccination and that gets changed to three doses, then we're going to actually have a significant public conversation about what's the risk and benefit,” Furness said. “Once we have enough significant public conversation, people will start to consider it … [otherwise] it'll seem like just a bureaucratic move.”

Having an open conversation about the role vaccines play in the fight against COVID-19 will be especially helpful in targeting those who are doubtful or afraid of getting vaccinated, Furness said. Part of the solution also lies in increased education on the function of vaccines as well as improved public health messaging and more local engagement, Furness said.

“It's that afraid, doubtful, somewhat skeptical [group] that is not sure who to believe, and anyone in that category is going to default to doing nothing until you make a good case – that's where there's work to be done,” Furness said.

Based on his observations, appetite for vaccine mandates across Canada remains low at the moment, said Muhajarine. But one scenario in which he could see these rules being reintroduced on a provincial level is if governments see another wave of cases, or if another variant or sub-variant were to surface, he said. In that situation, it’s critical that officials not wait too long to act, said Muhajarine.

“Provincial governments have the authority and responsibility to introduce policies that will keep their population safe,” he said. “Throughout COVID-19, what we have learned is that quick action really matters. We cannot wait around until COVID starts to really hurt us in order to act against it.”

Furness also said that as pharmaceutical companies get closer to developing an Omicron-specific vaccine, it’s likely to encourage more people to get their third dose if they have not done so already.

“If we can come back and say, ‘Look, the vaccine is back to being what a lot of people want to understand,' which is what is my reduction in risk of getting infected … I think it will put more wind in the sails,” Furness said. “And it'll make it easier to maintain vaccine mandates.”

While Furness said a case could be made for waiting until a variant-specific vaccine is developed before considering revising the definition of fully vaccinated, he and other experts recommend that those who are eligible get vaccinated sooner rather than later.


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