BARRIE -- As the push to vaccinate all eligible Canadians against COVID-19 continues, some people are already due for their booster shots.
On Friday, the National Advisory Committee for Immunization (NACI) released updated guidance regarding COVID-19 booster shots in Canada, outlining several subsections of the country鈥檚 population that should receive a third jab at least six months after their primary vaccine series.
The committee said it 鈥渟trongly recommends鈥 mRNA booster shots be offered to those aged 50 and over, seniors living in long-term care homes and other congregate living facilities and to those who received a complete series of a viral vector COVID-19 vaccine, such as Johnson & Johnson or AstraZeneca.
NACI also strongly recommends booster shots be offered to First Nations, Inuit and Metis peoples, as well as frontline healthcare workers who are in direct contact with patients.
The agency also recommends that booster doses may be offered to those between the ages of 18 and 49, at least six months after they received their primary vaccine series.
But what is a booster shot, and will everyone eventually need one? Here鈥檚 what experts say.
WHAT IS A BOOSTER SHOT?
COVID-19 booster shots are just a third dose of the initial vaccine, Dr. Matthew Miller, an associate professor at McMaster University鈥檚 department of biochemistry and biomedical sciences, explained.
鈥淔or example, people who got two doses of an mRNA vaccine, the booster shot would be a third dose of the same vaccine -- same dose and same contents,鈥 he told CTVNews.ca in early November.
Miller said that is similar to what you see with most conventional booster shots.
He said people receive the same vaccine multiple times in order to 鈥渟trengthen the immune response that鈥檚 elicited against the contents of the vaccine.鈥
Dr. Isaac Bogoch, an infectious diseases faculty member at the University of Toronto, said 鈥渟emantics matter,鈥 adding that COVID-19 boosters should really just be referred to as a third dose.
Bogoch said many vaccines are administered in three doses, and pointed to the Hepatitis B vaccine as an example.
鈥淪o I think we should be thinking of this as a three-dose vaccine series,鈥 he told CTVNews.ca in early November.
According to Bogoch, it is 鈥渧ery likely鈥 that most people will require a third COVID-19 vaccine.
鈥淢ost of us are two doses in to a three-dose vaccine series,鈥 he said.
IS A THIRD DOSE NECESSARY?
Bogoch said there are a few reasons a third dose of COVID-19 vaccine is necessary.
He said some people don鈥檛 mount as strong of an immune response as others 鈥 namely the elderly and those who are immunocompromised.
Bogoch said they can 鈥渃ertainly benefit鈥 from a third dose of the vaccine 鈥渙n the sooner end of the spectrum.鈥
According to Bogoch, another reason for administering a third dose is to combat waning immunity and protection, which could happen over time.
鈥淲aning protection really referring to breakthrough infections,鈥 he said. 鈥淪ome studies overestimate the degree of it, but it鈥檚 still there and it鈥檚 clear that people will need a third dose to help prevent that from happening.鈥
Bogoch said another reason a third dose should be administered is to help further reduce the risk of severe outcomes and death, as well as reduce the risk of getting the infection in the first place.
He pointed to a , which found those over the age of 60 who had received a third dose of the vaccine were 19.5 times less likely to have severe COVID-19 than those of the same age who had only received two shots.
鈥淪o I think it鈥檚 safe to say that most people will be getting a third dose and the reason they will be is because this should really be a three-dose vaccine series,鈥 he said.
Miller echoed Bogoch鈥檚 remarks, saying he thinks it is 鈥渋nevitable鈥 that everyone will eventually need a third dose of the COVID-19 vaccine.
He added that NACI is making 鈥渆vidence-based recommendations鈥 when it comes to who receives their third dose and when, in a way that will 鈥減rotect vulnerable populations.鈥
HOW DO RESEARCHERS KNOW IF ANOTHER DOSE IS NEEDED?
When it comes to determining whether an additional dose of a vaccine is necessary, researchers look at a few different things, Miller said.
First, researchers will study the effectiveness of the initial vaccine series. They do this by monitoring effectiveness in large populations, Miller explained.
鈥淲hat we want to see is steady protection as we get months from completion of the primary vaccine series,鈥 he said. 鈥淲hen we start to see that dropping, that鈥檚 really the most important signal that a booster may be necessary.鈥
In addition to monitoring its effectiveness, Miller said some researchers will also look specifically at the immune response the vaccine is producing.
鈥淪o they look at things like antibodies in people鈥檚 blood, or cells in people鈥檚 blood -- immune cells -- and look to see what happens with the numbers of those things,鈥 he said. 鈥淭hat鈥檚 a more imperfect measure than looking at effectiveness directly, but it can also give us signs of when a booster might be necessary.鈥
WILL CANADIANS NEED COVID-19 SHOTS EVERY YEAR?
Both Miller and Bogoch said it鈥檚 too soon to know whether Canadians will need COVID-19 vaccines every year.
鈥淚t might be an annual thing -- it might not be, no one really knows,鈥 Bogoch said. 鈥淚 think if anyone speaks with a high degree of confidence on this we should be suspicious because we don鈥檛 really know.鈥
Miller said this is something that 鈥渟till requires pretty intensive investigation.鈥
鈥淥n one hand, it鈥檚 a decision that鈥檚 going to be impacted by how long we see immunity last,鈥 he explained. 鈥淏ut that鈥檚 also related to how much the virus is circulating [and] how much the virus is evolving.鈥
Miller said researchers are monitoring these things in real-time, every day to help inform those decisions.
VACCINES ADMINISTERED OVERSEAS
While Canada begins administering third doses to those in need, Miller said the country should also 鈥渟till be thinking really carefully鈥 about the other places in the world where people have not yet received even their first jab.
Miller said ensuring people in other parts of the world have access to COVID-19 vaccines will 鈥渞eally help Canada too.鈥
鈥淭he lower the infection rates are internationally, the lower the probability of problematic variants emerging will be,鈥 he explained.
Miller said making sure other countries have sufficient quantities of vaccines for their populations, and ensuring third doses are available to those in Canada who require them should be 鈥減arallel priorities.鈥
