Any vaccinated Canadian who gets infected with SARS-CoV-2 should wait three months before getting a COVID-19 booster shot, Canada’s National Advisory Committee on Immunization (NACI) now recommends.
The new guidance comes as millions of Canadians have become infected in mere weeks, thanks to the fast-spreading, immune-evasive Omicron variant — and amid a patchwork of provincial recommendations and lower access to testing that can confirm whether people even had COVID-19.
In the Canada-wide recommendations, released on Friday, the NACI team said a longer interval between infection and vaccination “may result in a better immune response as this allows time for this response to mature in breadth and strength, and for circulating antibodies to decrease, thus avoiding immune interference when the vaccine is administered.”
At this point, there is “insufficient clinical or real-world data” to inform guidance on the ideal interval between infection and vaccination, NACI noted, with the advisory body instead relying on available data and the basic principles of vaccinology and immunology.
For vaccinated individuals aged 12 and up who are eligible for a third dose, the recommendations suggest waiting three months after the onset of symptoms, or following a positive test for anyone who was asymptomatic — while also being at least six months out from a second dose.
Those who experienced SARS-CoV-2 infection before starting or completing their primary COVID-19 vaccine series may receive their next dose eight weeks after symptoms started or after testing positive, according to the guidelines.
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NACI also recommends tighter vaccination timelines for certain individuals who get infected with SARS-CoV-2 before getting fully vaccinated, including:
- People aged five and up, who are moderately to severely immunocompromised but have no previous history of multi-system inflammatory syndrome in children (MIS-C), may receive a vaccine dose four to eight weeks after symptom onset or a positive test.
- People aged five and up, and with a previous history of MIS-C, regardless of whether they’re immunocompromised, may receive a vaccine dose after recovery or 90 days since the onset of MIS-C, whichever is longer.
‘Reasonable’ guidelines, virologist says
Angela Rasmussen, a virologist and researcher with the University of Saskatchewan’s Vaccine and Infectious Disease Organization, told CBC News that overall, the new Canadawide guidelines seem “reasonable.”
“There’s evidence that longer intervals between immune exposure [through vaccination or infection] results in more durable immunity,” she said. “So letting the immune system return to baseline prior to boosting makes sense to maximize the response the booster will elicit.”
As CBC News previously reported, it’s ideal to get vaccinated after your immune system has calmed down following an infection, both to ensure it isn’t already busy fighting off a pathogen and so it responds well to the vaccine dose.
There’s also a growing body of evidence that having all three vaccine doses offers strong protection, particularly against severe health outcomes, if someone winds up infected with the now-dominant Omicron variant.
And there’s early signals that layering vaccination and infection may offer broader immunity than just infection alone.
But NACI’s recommendations also arrived amid a confusing time for Canadians.
There’s a wide variety of provincial guidance across the country, with recent suggested timeframes on post-infection vaccination ranging from B.C. and Quebec’s suggestions to simply wait until your symptoms go away to a recommendation from Ontario’s top doctor to hold off for 30 days.
The NACI suggestions also follow shifts in various provincial testing strategies, which mean fewer Canadians have access to gold-standard PCR tests to know for sure when — or if — they had a SARS-CoV-2 infection in recent weeks.
Dr. Zain Chagla, an infectious diseases specialist and associate professor at McMaster University in Hamilton, said those factors will make it tough for many Canadians to gauge when to get a booster post-infection.
People who are unable to get a COVID-19 test in the community can’t assume they caught the virus, he noted, since a good chunk of people coming to hospitals with respiratory symptoms right now actually wind up testing negative because they’re actually battling other seasonal viruses.
“It certainly makes it a lot tougher in an era where more people couldn’t get tested,” he said.
Samantha Yammine, a Toronto-based science communicator, stressed that Canadians who followed local guidelines and got a booster shot in a shorter timeframe than NACI’s new advice shouldn’t feel like they made the wrong decision.
The guidance seems geared toward optimizing people’s boosters for longer term durability of immunity, she said, but the shots are still “safe and effective at any of the recommended timelines.”
“If you haven’t been boosted yet, then hopefully the provinces and territories apply these new recommendations as relevant to their local epidemiology,” Yammine said.
“If you’re in a high risk job or particularly vulnerable and don’t want to wait to get boosted, talk to a member of your health team. There’s a line in the NACI recommendations that says individuals should interpret these in the context of their own health risks.”
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