Canada's National Advisory Committee on Immunization (NACI) is recommending COVID-19 booster shots for all adults 80 years of age and older, and is also opening the door for certain other groups who may be at increased risk of lowered protection over time since their initial vaccinations.
"Populations at highest risk of waning protection following their primary series and at highest risk of severe COVID-19 illness should be offered a booster dose of an mRNA COVID-19 vaccine at least six months after completing their primary series," NACI's new guidance released Friday said, noting that seniors 80 years and older "should" be offered a booster shot.
NACI also said other people "may" be offered a booster shot, because they "may be at increased risk of lower protection over time since vaccination, increased risk of severe illness or who are essential for maintaining health system capacity."
Although NACI makes recommendations, it's up to the provinces and territories to decide who they will offer booster shots to.
Those groups include:
Adults between the ages of 70 and 79.
Anyone who received two doses of the AstraZeneca/COVISHIELD vaccine or one dose of the Johnson & Johnson/Janssen (J&J) vaccine.
Adults in or from First Nations, Inuit and Métis communities.
Adults who are front-line health-care workers who have direct in-person contact with patients and who were vaccinated with a very short interval between their first and second doses (three or four weeks).
Booster shots should be given at least six months after the second dose of vaccine, NACI said. The boosters should also be one of the mRNA vaccines — Pfizer-BioNTech or Moderna, it said.
In Alberta, Indigenous people age 65 and older and other seniors who are 75 and older can already get booster shots.
On Thursday, the Northwest Territories announced anyone 18 years of age or older will now be eligible for a booster shot.
Last week, British Columbia said that seniors age 70 and older, all Indigenous people 12 and older and health-care workers who only had three or four weeks between their two doses will all be able to get a booster shot by the end of the year. By next May, everyone in B.C. will be eligible for one.
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After NACI's guidance was released on Friday, the Ontario government said it would release its plan for COVID-19 boosters next week.
Why would people who got two doses of AstraZeneca need boosters?
Those who got viral vector vaccines — two doses of AstraZeneca (authorized in Canada) or one dose of J&J vaccine (a single-dose vaccine authorized in the U.S.) — are on the list for a booster because evidence has shown they have "somewhat lower initial vaccine effectiveness" and people who got those shots "may become susceptible to infection sooner than people who received a primary series that included at least one dose of an mRNA vaccine," NACI said.
What's the difference between a booster shot and a 3rd dose?
The three approved COVID-19 vaccines in Canada (Pfizer-BioNTech, Moderna and AstraZeneca) are all two-dose regimens. A third dose is for people who may not have mounted a strong enough immune response to fight off COVID-19 after two doses.
NACI has recommended third doses for elderly people living in long-term care and those who have specific health conditions that make them immunocompromised. For these people, a third dose is an extension of their primary series of vaccinations.
A booster shot is for people who likely had a fulsome immune response to the regular two-dose vaccine regimen, but "with time, the immunity and clinical protection has fallen below a rate deemed sufficient in that population," according to the World Health Organization (WHO).
It's comparable to the tetanus vaccine, which requires a booster shot every 10 years. Most experts agree that everyone will likely need a COVID-19 booster shot at some point within the next year, but the big question is when.
Residents of long-term care homes, immunocompromised already prioritized
In its guidance on Friday, the advisory group said it continues to "strongly recommend" that people who are moderately to severely immunocompromised should get a third dose of vaccine. People in that category include:
Those in active treatment for solid tumour or blood cancers.
Organ transplant recipients taking immunosuppressive therapy.
People getting chimeric antigen receptor (CAR)-T-cell therapy or hematopoietic stem cell transplant (within two years of transplantation or taking immunosuppression therapy).
People with moderate to severe primary immunodeficiency (e.g. DiGeorge syndrome, Wiskott-Aldrich syndrome).
People with Stage 3 or advanced untreated HIV infection and those with AIDS.
People receiving active treatment with certain immunosuppressive therapies.
Why doesn't Canada just offer boosters to everyone?
In a media briefing on Friday, Dr. Theresa Tam, Canada's chief public health officer, said it was "possible" that there could be a national recommendation for everyone to get COVID-19 boosters at some point — but not now.
At this point, "a primary series of the vaccines [still] provides good protection to the general public," Tam said, adding that boosters could be rolled out in a "phased approach" over time — just as the initial vaccinations were.
Dr. Christopher Labos, a cardiologist and epidemiologist in Montreal, agreed.
"The majority of the population does not need a booster shot right now, but ... it is reasonable to do it in certain high-risk groups," Labos told CBC News Network on Friday after the announcement.
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Another big reason, many health experts say, is "vaccine equity." Much of the world, particularly Africa, hasn't even received a first dose yet, according to WHO.
WHO has repeatedly pleaded with rich countries to stop giving what it considers unnecessary booster shots to people who are already protected against COVID-19 so those vaccines can be redirected to developing countries.
"We're planning to hand out extra life-jackets to people who already have life-jackets, while we're leaving other people to drown without a single life-jacket," Dr. Mike Ryan, head of the World Health Organization's health emergencies program, said during a news conference in August.
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Many infectious disease and immunology experts agree that in addition to the ethical considerations, it's in Canada's best interest to help ensure people in developing countries get the COVID-19 vaccines they need.
That's because the longer the coronavirus that causes COVID-19 can circulate among unvaccinated people, the more likely it is to mutate into new variants that put everyone at increased risk.
"These vaccines are precious," Dawn Bowdish, Canada Research Chair in aging and immunity and a professor at McMaster University in Hamilton, said in a previous interview with CBC News. "If we want to make sure there's not the next variant and the variant after that and the variant after that, we really need to get the world vaccinated."
I keep hearing about 'waning immunity.' Does that mean I need a booster?
The term "waning immunity" usually refers to a decrease in antibodies over time. After any vaccination, immunologists and virologists say, it's normal for antibody levels to go down.
But the immune system is much more than antibodies. B cells and T cells are also hard at work. B cells produce antibodies and if they're exposed to the virus again, they "remember" and can make more. T cells target and get rid of infected cells.
A study published in the journal Science found "robust cellular immune memory" from B cells for at least six months after mRNA vaccination against all circulating strains of the virus — even the highly contagious delta variant.
Many experts agree that having waning antibodies does not automatically translate into a need for a booster shot.