The National Advisory Committee on Immunization (NACI) is now "strongly recommending" that all Canadians over the age of 50 and other vulnerable individuals — such as health care workers, Indigenous people and those living in congregate care settings — get a third dose of an mRNA COVID-19 vaccine.
In a new report issued today, NACI — an independent body made up of volunteer vaccine experts — also calls on Canadians aged 18 to 49 to get a third mRNA shot at least six months after they got their second.
With the virus still circulating widely, advisory panels in other countries — such as the one that works with the U.S. Centers for Disease Control (CDC) — have been recommending for weeks an expansion to the booster shot campaign to cover more people.
NACI's recommendation gives the provinces and territories the leeway to dramatically expand the currently limited booster shot campaign.
The COVID-19 vaccines authorized by Health Canada have proven to be very effective against infection, severe disease, hospitalization and death. NACI said it's recommending booster shots now because emerging data suggests that protection against infection is decreasing over time for those who completed a two-dose vaccine regimen.
"Decreasing protection against infection could contribute to increased transmission, since infected individuals may be a source of infection for others," the committee said in its report. "Therefore, a booster dose may provide more durable protection to reduce infection, transmission, and in some populations, severe disease."
NACI also published guidance today on which mRNA shots should be given to people aged 12 to 29.
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A small number of young people — mostly men and boys — have experienced inflammation of the heart muscle post-vaccination. NACI said it's less common in people who've had the Pfizer product instead of the Moderna shot. The committee said that, among people aged 18-29 eligible for a booster, Pfizer should be administered for that third shot.
While NACI says all adults 50 and older should get a third shot, it's not insisting that younger people get a booster. It says that a third dose is "strongly recommended" for people 50 and older, while a booster for people 18 to 49 years of age is a "discretionary recommendation."
Dr. Theresa Tam, Canada's chief public health officer, said NACI is pushing boosters for the 50+ group in particular because they're more at risk of severe outcomes from COVID-19.
The softer recommendation for younger people is meant to signal to the provinces that older Canadians should get boosters first, Tam said.
"Everyone is trying to focus on the groups at highest risk and I hope that the NACI recommendation provides some guidance on which age groups should receive the strongest focus," she said. "Provinces will take into account their population, their demographics and the risk factors."
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"The data we have at the moment suggests vaccines are holding up pretty good against severe outcomes. But there is certainly a downward directional travel in terms of the waning of the vaccine effectiveness over time against asymptomatic infection and any symptoms."
NACI says the 18-49 cohort should consider local epidemiological conditions (case counts in a given area), any underlying health conditions and the time that has elapsed between their first and second doses before rolling up their sleeves for a booster.
Dr. Matthew Tunis, executive secretary to NACI, said early evidence suggests people who had a short interval between their first two doses may face a higher risk of waning protection and should consider getting a booster as soon as they're eligible.
While Pfizer and Moderna have recommended that a second shot be administered 21 or 28 days after the first, Tunis said a longer time span between those first two shots may actually offer more protection for a longer period of time.
NACI reviewing terminology
While NACI is using the term "booster dose" for this third shot, the committee said it's also reviewing emerging evidence that suggests a third shot should be considered part of the "primary series" — that a person shouldn't be considered fully vaccinated until they've had three doses of an mRNA product.
"NACI will adjust the terminology as required," the committee said.
While recommending booster doses for all adults, NACI said the top priority for provinces and territories right now should be getting shots to people who have not yet had their first two doses.
Rates of new COVID-19 infections, hospitalizations, ICU admissions and mortality continue to be highest among unvaccinated individuals, the committee said.
Tam said NACI's booster advice is not driven by the emergence of the new omicron variant, a potentially more transmissible strain.
She said NACI was already considering an expansion to the booster shot campaign when South African officials reported omicron to the World Health Organization.
"They were already scheduled to have their discussions on this next set of recommendations. It's not because of omicron but I think it's timely because we're really watching the omicron variant," she said.