OTTAWA -- Seeking to stamp out confusion over what should be made of the advice coming from a federal panel of medical experts that second COVID-19 vaccine doses should be delayed by up to four months, federal health officials say that the latest guidance is meant to “complement, not mirror” the official Health Canada authorizations for use of these vaccines and that Canadians should expect the advice around the best administration strategy to keep changing.

Late Wednesday, the National Advisory Committee on Immunization (NACI) issued new guidance advising that the window between shots for all three of the currently approved vaccines—Pfizer-BioNTech, Moderna, and AstraZeneca—can now be delayed by up to four months, while still being effective.

The approach of holding off on administering all second doses by four months is in contrast with what Health Canada’s authorization of these vaccines initially indicated: that the second Pfizer dose was to be delivered around 21 days after the first, that the second Moderna shot was to be given around 28 days after the first, and that the AstraZeneca second dose should be given between four and 12 weeks after the first.

Seeking to offer some clarity around the role Canada's National Advisory Committee on Immunization (NACI)’s COVID-19 vaccine usage advice is supposed to play, Deputy Chief Public Health Officer Dr. Howard Njoo said Thursday that the latest guidance is meant to “complement, not mirror” the official Health Canada authorizations for use of these vaccines.

Njoo said that the difference in messaging from the two national bodies is different by design, indicating provinces should consider both the Health Canada directives and expert advice in plotting their ongoing vaccine rollout strategies.

“You have likely noticed that NACI’s recommendations are sometimes different, possibly broader or narrower than the conditions of vaccine use that Health Canada has authorized. As the regulator, Health Canada authorizes each vaccine for use in Canada according to factors based on clinical trial evidence, whereas NACI bases its guidance on the available and evolving evidence in a real-world context, including the availability of other vaccines,” Njoo said.

NACI says it’s come to this conclusion after considering evidence from recent scientific studies and “real world effectiveness,” that show high levels of protection after one shot. Though the data remains limited and is still evolving around the best time frame to administer the first and second shots of the three currently approved vaccines, which are all two-dose regimens.

Seeking to further explain the process and why there appears to be contrasting guidance coming from the national level, Health Canada’s senior media adviser Dr. Supriya Sharma said that while the messaging would be simpler if there was one set of data and it never changed, “that's not what science does.”

“We want to make sure that people have confidence in the decisions that are being made about vaccines, whether it's at the level of the regulator or broader recommendations from NACI or the provinces and the territories… It’s really important that people know that this is going to be changing. We’re in this place now where we have multiple vaccines that are authorized, we have huge mass vaccination campaigns that are ongoing around the world, and the responsible thing to do is to make sure that we get all that information and incorporate that into our decision making,” she said.


While NACI’s advice are recommendations and not rules, which allows provinces to continue to tailor their vaccination rollout campaigns to fit the pandemic reality in each region, the new suggested approach has already been adopted by several provinces in recent days.

Njoo explained Thursday that while it seems the major change in goalposts of the vaccination strategy seems like it happened very fast, it followed NACI briefing provincial health authorities over the weekend.

“What happened then is that some provinces… have come out publicly in terms of moving forward with obviously the good information and evidence that they heard on Sunday, and so you're seeing that play out in real time, with various provinces that already are coming forward with their thinking based on the information and the evidence that NACI presented on the weekend,” he said.

NACI’s new guidance makes the case that with limited supply of COVID-19 vaccines, prioritizing first doses would allow jurisdictions to maximize the number of people being immunized with a first dose offering an initial amount of immunity earlier on, though it remains to be seen how the logistics of the rollout would have to be adjusted to adopt this approach.

Speaking about his provinces decision to delay the second dose by up to four months during a press conference with other premiers on Thursday, British Columbia Premier John Horgan said the decision was “a pretty simple” one to make.

“We want to get as many first doses in place as we can, and as the procurement of the federal government starts to ramp up in quarter three is the time to go back and get those second shots in place,” he said. “We believe this is the right way forward.”

Similarly, Alberta Premier Jason Kenney said that while NACI’s guidance was a factor, there has also been real-world examples in countries who are farther ahead in vaccinating its citizens indicating a longer window between shots is an effective strategy.

Kenney also pointed to the slow rollout of doses so far, saying the provinces have “no choice” but to extend the interval between in order to “get more people covered” to move towards a larger amount of population immunity quicker.

New Brunswick Premier Blaine Higgs said adopting the second dose delay will help see that province’s borders open up. “We're focused on this spring and getting ourselves back to normal this spring, and I think we can do that,” he said.

Maj-Gen. Dany Fortin who is leading the national logistics of the vaccine rollout said Thursday that it’s possible that coupled with additional vaccines being approved and larger shipments coming in the months ahead, the overall timeline could be accelerated. But, but for now the end of September remains the target they are planning to meet has reached out to Health Minister Patty Hajdu’s office to inquire whether the federal government has a comment on the shifting approach of prioritizing first doses for more people before moving to inject second doses months later.

In response Cole Davidson, a spokesperson for the minister, said that the Liberal government “will always support evidence-based decision making based on the latest data from experts.”


The infectious diseases, immunology, pharmacy, epidemiology, and public health experts who make up this advisory body are considered arms-length to the government. The panel makes recommendations to the Government of Canada for the use of vaccines approved for use in Canada based on analysis of “the best current available scientific knowledge at the time.”

The body has been in existence since 1964 advising on various new vaccines, but since the onset of the pandemic, it has been predominately focused on COVID-19 vaccines and the prioritization of them. It reports to the Infectious Disease Prevention and Control Branch of the Public Health Agency of Canada.

Njoo said that NACI will continue to monitor evidence on the effectiveness of a delayed second dose and “will adjust recommendations as needed.”