COVID-19 Booster Shots: Will You Need More Than One?

Earlier this month, Canada’s National Advisory Committee on Immunization strongly recommended that booster shots be administered to Canadians aged 50 and older, as well as other at-risk groups. While each province and territory has enacted its own policies on booster eligibility, third doses are being offered in varying degrees across the country.

With such a strong emphasis on booster shots, is it possible Canadians may need a fourth vaccine dose for ongoing protection against COVID-19?

According to Dr. Brian Conway, an infectious disease expert and medical director of the Vancouver Infectious Diseases Centre, it’s too early to say whether a fourth dose might be needed any time soon. Still, he said it’s likely that an annual booster shot will be necessary to strengthen the body’s immune response, something he anticipates will be seen in the fall to coincide with flu season.

“I think it’s premature to conclude that that will be needed in the short to medium term,” Conway told in a phone interview on Wednesday. “But that’s what I’m really seeing – a yearly COVID shot along with the flu shot, and COVID will become more manageable.”

A lot of this depends on the efficacy of these vaccines, Conway said, particularly against Omicron. Earlier this year, both Pfizer and Moderna reported strong effectiveness in their vaccines until about four to six months after they’ve been administered. But it remains to be seen just how successful booster shots will be in fighting off the new variant, and for how long.

“This is a bit of a moving target,” Conway said. “We’ve now realized that Omicron is going to take over the epidemic, and that vaccine protection against Omicron is probably significantly less over time.”

Some of this uncertainty is reflected in the different timelines for booster eligibility implemented across provinces and territories. Starting in January 2022, for example, adults in British Columbia will be eligible for their booster shot six to eight months after getting their primary series. Meanwhile, in Ontario, the minimum interval was recently lowered to just three months or 84 days.

But it’s really only after people have gotten their third dose that experts can assess its efficacy against Omicron and decide when a fourth shot might be needed, Conway said. Still, he foresees annual booster shots being given out in the fall.

“The question of whether the fourth shot will be needed before next fall, we will be able to answer in February or March, depending on how the epidemic evolves,” he explained. “Meaning if we’re seeing more cases, especially among triply vaccinated individuals, then it is at that point that we will decide if a fourth shot is needed before next fall.”


According to Conway, the COVID-19 pandemic is evolving similarly to the previous influenza pandemic, spreading in waves before it transformed into an endemic virus. He also pointed to a resemblance in the ways they’re transmitted, namely through person-to-person contact with the release of particles containing the virus through coughing or sneezing.

“The similarity of the seasonality and the modes of transmission speak to me, as they will both become endemic and require yearly shots,” he said.

Moderna also appears to be gravitating towards the idea of an annual booster shot. The pharmaceutical company recently announced it is working with Novavax on a single-dose vaccine that combines a COVID-19 booster shot with an experimental flu shot. The vaccine has since begun clinical trials.

“They’ve made up their minds that there will likely be yearly COVID shots,” said Conway. “Big Pharma doesn’t invest money in developing a product unless they think there will be a market for it.”

Based on a recent study published by the British Medical Journal, researchers discovered it was safe to administer a second dose of the COVID-19 vaccine and a flu vaccine at the same time, as long as they were given in different arms. The study also showed that doing so did not affect the immune response to either vaccine. The study was recently published as a preprint and is yet to complete peer review.

Still, experts insist more time is necessary to evaluate the situation. Last weekend, Dr. Anthony Fauci, the United States’ top infectious disease expert, stated that while he isn’t ruling out the possibility of annual booster shots in the future, it’s too early to determine whether they’re needed.

“It’s tough to tell,” he said in the interview that aired on ABC News. “You don’t know that…until you just follow it over a period of months.”

Earlier this month, Dr. Matthew Miller, an associate professor at McMaster University’s department of biochemistry and biomedical sciences, said this question “still requires pretty intensive investigation.

“On one hand, it’s a decision that’s going to be impacted by how long we see immunity last,” he explained. “But that’s also related to how much the virus is circulating [and] how much the virus is evolving.”

Conway’s best advice for now?

“Go get your third shot as soon as you’re eligible for it, and stay tuned.”

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