The U.S. has authorized booster shots of Pfizer’s COVID-19 vaccine for certain high-risk groups, and experts say Canada should consider doing the same.
On Wednesday, the FDA authorized booster shots for people aged 65 and older and people aged 18-64 who are at high risk of severe COVID-19.
In a separate vote Thursday, the CDC voted to recommend that booster shots should be made available to people aged 65 and over, as well as to adults aged 50-64 with underlying medical conditions. Younger adults could choose to receive a booster based on individual calculations of benefit and risk.
The FDA also said that people aged 18-64 whose institutional or occupational exposure puts them at risk of developing severe COVID-19 — which would include people who live in correctional facilities, teachers or health-care workers — could also receive a third dose. This proposal did not pass a CDC vote.
People who have occupational exposure to COVID-19 could include a lot of different groups, said Dr. Ellen Eaton, an assistant professor of medicine in the Division of Infectious Diseases at the University of Alabama at Birmingham. Even just including people with underlying medical conditions could mean a lot of people potentially eligible for boosters, she said.
“I want to remind everyone that those who are high risk for severe infection, that encompasses a lot of Americans,” she said. “A lot of Americans are not only living over 65, but have obesity, diabetes and other chronic conditions that we know are going to put them at higher risk of severe disease.”
Data suggests that there may be waning durability for these people after six months, she said, so the FDA is now encouraging doctors to consider boosters for these people.
“I think those recommendations are very reasonable,” said Alyson Kelvin, a virologist at the Vaccine and Infectious Disease Organization – International Vaccine Centre at the University of Saskatchewan.
These groups are “highly vulnerable” when it comes to either producing a strong immune response, or fading longevity of their vaccine, she said. “So it makes sense that these groups would be put forth for a booster. It might not make sense for the general public, though, healthy adults and adolescents, to be put forth for boosters.”
Canada’s National Advisory Committee on Immunization (NACI) currently recommends that people who are moderately or severely immunocompromised receive a third dose of vaccine. They are careful to note however that this is different from a “booster shot” — this additional dose is needed because these people never developed an adequate level of immunity after two doses.
NACI is still reviewing whether booster shots would be needed in the broader population.
It “makes sense” for Canada to look at giving third doses to the same kinds of populations identified by the FDA, Kelvin said, though she cautions that Canada’s situation is not exactly the same as the American one.
“We know that the U.S. rolled out the vaccine programme with quite a short time in between the first and second doses. We know that that type of vaccination schedule does lead to possibly a shorter protection time following the second vaccination,” Kelvin said.
“Whereas if you wait longer, as we did in Canada, this might offer longevity in your protection.” This is true of many vaccines, she added.
Another factor is that many Canadians have received two brands of vaccines: whether it was one dose of AstraZeneca and a dose of an mRNA vaccine, or a mix of Pfizer and Moderna, Kelvin said.
“If we go back to classical vaccinology, what we know of how you’re vaccinated, mixing different types of vaccines may lead to better overall response and again, a longer immune life. So I think with this the idea of mixing, we might have a better response and not need a booster as fast,” she said.
Jason Kindrachuk, an assistant professor and Canada research chair in emerging viruses at the University of Manitoba, thinks that nailing down the specifics of how a vaccine booster program would work could be difficult, particularly since researchers have less than two years of data showing how vaccines work in different groups.
“I think we have to be very considerate about what actually defines people that are high risk,” he said.
Canada should examine eligibility for third doses, he said, but not all the data is there yet.
“Listen, it’s been a global pandemic for, what, 19 months now, 20 months now?” he said. “We are, I think, still trying to identify all of those high risk groups, certainly trying to tease apart which underlying health conditions are truly linked to more severe disease or risks of more severe disease.
“It’s not necessarily easy to do.”
While she believes it’s possible that years from now, the average Canadian might get a booster shot for COVID-19 because the virus has evolved, Kelvin notes that right now, boosters for everyone shouldn’t be the priority.
“I think what’s really important is that to get us as a community out of this pandemic, we need large amounts of the population to be vaccinated,” she said. Even with a booster shot, you will still be exposed to the virus if there is lots circulating in your community, she said.
“Really, the most protective thing that you could get is working with your community and getting those vaccination rates up.”
— with files from Global News’ Jackson Proskow and the Associated Press
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