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Should you wait to get your 4th COVID-19 vaccine dose? There's no simple answer


COVID-19 case counts in Canada are on the rise yet again, prompting some experts to claim the country is now in a summer wave.

As infections climb, several provinces are beginning to expand their eligibility requirements for fourth doses of the COVID-19 vaccine. The most recent example is Ontario, which will allow residents aged 18 and older to get their second booster shot starting July 13.

But with a new bivalent vaccine likely on the horizon, which is expected to better target the Omicron variant, many Canadians may be left wondering whether they should wait for this new vaccine instead of getting their fourth dose once they’re eligible.

According to Dr. Isaac Bogoch, an infectious disease expert and faculty member at the University of Toronto, those who are older or have underlying health conditions would benefit from getting vaccinated as soon as possible.

“People who are at greatest risk for severe infection should be getting a fourth dose if the question is asked in July,” he told in a telephone interview on Wednesday.

According to the Public Health Agency of Canada, those who are older in age – particularly above the age of 60 – and those who are immunocompromised are more likely to suffer from severe illness following a COVID-19 infection, such as hospitalization or death.

However, for younger Canadians who are relatively healthy, an argument could be made for waiting to receive a booster shot in the fall, Bogoch said. Vaccine manufacturers such as Pfizer and Moderna have announced the development of vaccines designed to better target the Omicron variant, which could be ready to roll out by the fall.

“It’s certainly something that needs to be considered,” he said. “[Some] people might stand to benefit from waiting for updated vaccines.”

In a tweet shared on Tuesday, Dr. Abdu Sharkawy, an infectious disease expert based in Toronto, urged Canadians over the age of 65 or with high-risk medical conditions to get their fourth dose sooner rather than later.

“Don’t wait for a fall booster. Get it now,” he tweeted. “Far too much risk of BA.5 getting you or someone more at risk.”


In a separate tweet, he recommends those who recently received their third dose but are not at high risk of developing severe disease should wait for an updated vaccine formula in the fall.

Dr. Kashif Pirzada, however, encourages Canadians to get their fourth dose as soon as they become eligible, provided it has been six months since their last dose of the COVID-19 vaccine. This is regardless of how old they are or whether they have underlying health conditions, he said.

“Even if you're younger … it's probably a good idea,” Pirzada, an emergency room physician based in Toronto, told on Wednesday in a telephone interview. “Getting a [second] booster could mean the difference between getting a very light infection … or getting a more severe infection that could lead to long-term COVID.”

While studies have shown a drop in the efficacy of current COVID-19 vaccines against Omicron, the formula continues to offer solid protection against severe disease as a result of COVID-19, particularly among those who have received three doses of the vaccine, Pirzada said. Clinical studies involving the protection offered by fourth doses are ongoing.

Getting a booster shot now also won’t prevent someone from receiving an Omicron-specific vaccine if one does become available in the fall, said Pirzada. Additionally, given the increasing amount of COVID-19 currently circulating in Canada, largely drive by the Omicron BA.5 sub-variant, the chances of getting infected is “very high,” he said.

“If you get a booster now and you get [another] booster in three months, it's not a big deal, it won't harm you,” Pirzada said. “You'll have that protection for this wave and whatever wave comes between now and when the [Omicron-specific] booster is available.”

According to the Public Health Agency of Canada, about 49 per cent of all Canadians have received three doses of a COVID-19 vaccine, while just nine per cent of Canadians have received four doses of a vaccine.


Current COVID-19 vaccines were designed to target the original strain of SARS-CoV-2, meaning they were made monovalent. However, the newer formulas being developed by both Pfizer and Moderna are bivalent, said Omar Khan, a professor of biomedical engineering and immunology at the University of Toronto. This means they target spike protein mutations present in the original strain of SARS-CoV-2, as well as Omicron.

“Even if the virus continues to evolve, hopefully these bivalent vaccines [will provide] the immune system with a nice, broad view of the coronavirus,” Khan told in a telephone interview on Wednesday. “The idea is to make antibodies that are broadly neutralizing for a variety of different types of coronavirus.”

According to The Canadian Press, Moderna applied to Health Canada for regulatory approval of its bivalent booster on June 30, with the goal of making the vaccine available in the fall. Pfizer is also working towards getting approval for its Omicron-specific vaccine in Canada, but the company did not provide a specific timeline for doing so.

While it’ is possible these bivalent vaccines may be ready to launch by fall, this isn’t guaranteed, Khan said, and it’s possible more time will be required by Health Canada to grant its approval.

Getting a COVID-19 booster shot now rather than later can offer ongoing protection until the new formula becomes available, Khan said.

“Having the fourth dose as an option is … a great option to provide a bridging solution while we wait for that fall approval,” he said. “It’s the opportunity to provide Canadians with more tools to ensure that they are staying safe.”

Both Moderna and Pfizer have said their vaccines that combine the original formula with protection against the Omicron variant resulted in a substantial boost in virus-fighting antibodies to target Omicron. However, clinical studies are still underway, Bogoch said.


The National Advisory Committee for Immunization (NACI) updated its recommendations on booster doses on June 29, and now strongly recommends Canadians 65 years of age or older be offered a COVID-19 vaccine booster dose in the fall, regardless of how many booster doses they have already received.

Additionally, the organization made a discretionary recommendation that Canadians aged 12 to 64 may also receive a booster dose in the fall, regardless of how many booster doses they have already received. However, eligibility requirements for fourth doses of a COVID-19 vaccine continue to vary from province to province, which has undoubtedly led to confusion among Canadians over when to get their booster dose.

“If people are confused about this, they have every right to be,” Bogoch said. “Confusion will lead to mistrust and … we need public trust and public buy-in.”

Ultimately, for those who are still unsure about when to get their fourth dose of the COVID-19 vaccine, Bogoch and Khan both urge Canadians to speak with a health-care provider to determine the best course of action based on their own individual health risks.

“It all depends on your situation,” Khan said. “You have to look at your underlying health conditions [and] risk of exposure.

“If you are questioning [getting your fourth dose], your best resource is your doctor.” Top Stories

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