BARRIE – The push continues to vaccinate all eligible Canadians against COVID-19, with some already due for their booster shots.

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On Friday, the National Advisory Committee for Immunization (NACI) issued updated guidance about COVID-19 booster shots in Canada, outlining several sub-segments of the country’s population that need to be treated at least one of its primary vaccine series. Should be received for the third time at least six months later.

The committee said it “strongly recommends” mRNA booster shots to people age 50 and older, seniors living in long-term care homes and other mass living facilities, and those who have a viral infection. Vectors receive the full range of COVID-19 vaccines, offered. Like Johnson & Johnson or AstraZeneca.

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NACI strongly recommends giving booster shots to First Nations, Inuit and Métis people, as well as to frontline healthcare workers who are in direct contact with patients.

The agency also recommends that people between the ages of 18 and 49 be offered a booster dose, at least six months after receiving their primary vaccine series.

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But what is a booster shot, and will everyone eventually need it? Here’s what experts say.

What is a Booster Shot?

The COVID-19 booster shots are just a third dose of the initial vaccine, said Dr., an associate professor in McMaster University’s Department of Biochemistry and Biomedical Sciences. Matthew Miller explained.

“For example, for people who received two doses of the mRNA vaccine, the booster shot would be the third dose of the same vaccine — the same dose and the same ingredients,” he told in early November.

Miller said this is what you see with most traditional booster shots.

He added that people receive the same vaccine multiple times to “strengthen the immune response against the vaccine’s ingredients.”

“Semantics matters,” said Dr. Isaac Bogoch, an infectious disease faculty member at the University of Toronto, adding that a COVID-19 booster should really only be referred to as the third dose.

Bogoch said many vaccines are given in three doses, and pointed to the hepatitis B vaccine as an example.

“So I think we should think of it as a three-dose vaccine series,” he told in early November.

According to Bogoch, it is “very likely” that most people will need a third COVID-19 vaccine.

“Most of us have two doses in a three-dose vaccine series,” he said.

Is a third dose necessary?

Bogoch said there are some reasons why a third dose of the COVID-19 vaccine is necessary.

He noted that some people do not have as strong an immune response as others – namely the elderly and those who are immune.

Bogoch said they could “definitely benefit” from a third dose of the vaccine “at the earliest end of the spectrum.”

Another reason for giving a third dose, according to Bogoch, is to combat weakened immunity and defenses, which can occur over time.

“Wanning protection is really talking about breakthrough infections,” he said. “Some studies overestimate the degree to which it is, but it is still there and it is clear that a third dose will be needed to help prevent this from happening to people.”

Bogoch said another reason why a third dose should be given is to help reduce the risk of serious consequences and death, as well as reduce the risk of getting an infection in the first place.

he pointed to a study from israel, which found that people over the age of 60 who received a third dose of the vaccine were 19.5 times less likely to have severe COVID-19 than people of the same age who got only two shots .

“So I think it’s safe to say that most people will get the third dose and the reason for this is that it should really be a three-dose vaccine series,” he said.

Miller echoed Bogoch’s remarks, saying he thinks it’s “inevitable” that everyone will eventually need a third dose of the COVID-19 vaccine.

He said the NACI is making “evidence-based recommendations” when it comes to who receives their third dose and when, in a way that “will protect vulnerable populations.”

How do researchers know if another dose is needed?

When it comes to determining whether additional doses of the vaccine are necessary, researchers look at a few different things, Miller said.

First, the researchers will study the effectiveness of the initial vaccine series. They do this by monitoring effectiveness in a larger population, Miller explained.

“What we want to see is stable protection as we get months into the completion of the primary vaccine series,” he said. “When we start to see that decline, it’s really the most important sign that a booster may be necessary.”

In addition to monitoring its effectiveness, Miller said some researchers will also look specifically at the immune response the vaccine is causing.

“So they look at things like antibodies in people’s blood, or cells in people’s blood — immune cells — and see what happens to those numbers of things,” he said. “This is a more incomplete measure than looking at effectiveness directly, but it can also give us an indication of when a booster may be necessary.”

Will Canadians need COVID-19 shots every year?

Both Miller and Bogoch said it was too soon to know whether Canadians would need COVID-19 vaccines every year.

“It could be an annual thing — it might not, nobody really knows,” Bogoch said. “I think if anyone speaks to this with a high degree of confidence we should be skeptical because we really don’t know.”

Miller said this is something that “still requires fairly thorough investigation.”

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

Miller said researchers are monitoring these things in real time every day to help inform these decisions.

Vaccines administered abroad

While Canada begins giving a third dose to those in need, Miller said the country should “still think really carefully” about other places in the world where people haven’t even got their first jab.

Miller said ensuring people in other parts of the world have access to COVID-19 vaccines “would really help Canada as well.”

“The lower the infection rate internationally, the less likely the problematic forms to emerge,” he explained.

Miller said making sure other countries have enough vaccines for their populations, and making sure Canada has a third dose available to people who need them, should be “parallel priorities.”