Delay between doses 'expected to be less' than 4 months as supply increases: Vaccine panel

The National Advisory Committee on Immunization (NACI) is standing by its recommendation to delay second doses of two-shot COVID-19 vaccines by up to four months, but is now acknowledging that given Canada’s increasing vaccine supply, not everyone will be waiting four months between their doses.

Officials from NACI, as well as provincial and federal health authorities, briefed reporters Wednesday on new data they have released to back up their dose delay recommendation.

“With Canada's expected vaccine supply, the interval between the first and second dose is expected to be less than four months,” said NACI Vice-Chair Dr. Shelley Deeks.  

NACI is projecting that as supply of vaccines increases in Canada the interval between shots will likely be closer to the initial guidance, with second doses being scheduled for a month and a half or two months after the first.

“In terms of supplies expected, it will eventually be possible to shorten that interval,” said NACI Chair Dr. Caroline Quach. 

After NACI made the initial guidance on March 3 to defer second doses up to four months after the first, with the aim of seeing Canada maximize the number of people being immunized, provinces largely shifted their vaccination strategies and started booking people’s second shots four months down the line.

The longer wait between shots is advice that is in contrast with Health Canada’s authorization of these vaccines, which follows the pharmaceutical companies’ guidance for shorter intervals between shots.

The arms-length federal vaccine advisory body’s new report points to both clinical trial and real-world data that shows the COVID-19 vaccines Canada is using, are offering strong levels of immunity after a single dose.

For example, NACI states that data from two clinical trials for the mRNA Moderna and Pfizer-BioNTech vaccines show that both vaccines had an efficacy of up to 92 per cent up until the second dose, while the first shot of the AstraZeneca vaccine is indicating a 76 per cent efficacy.

As well, NACI states that by delaying the second shot it’s offering increased protection to more people who under this strategy have been able to receive a single COVID-19 vaccine more quickly. Ideally this will increasingly lead to more controlled community transmission, though with the variants rapidly spreading throughout the country, Canada is in the midst of a third wave. 

In the full statement issued Wednesday, NACI writes that second doses should still be offered “as soon as possible after all eligible populations have been offered first doses, with priority given to those at highest risk of severe illness and death from COVID-19 disease.”

According to Deeks, Canada may be the only country advising an up to four-month delay between doses, but others have been using a three-month interval between shots.

“I know a number of jurisdictions are already under discussion about decreasing the interval based on where they are, [in their vaccine rollouts]” she said. 

The committee also noted Wednesday that jurisdictions continue to have the ability to opt for a shorter timeframe between the first and second doses, “based on local rates of cases and what is known about where transmission is happening, local vaccine supply, their local methods of delivering vaccine and emerging evidence.”

“Given the evidence that this strategy would have an important impact on reducing deaths and hospitalisations, NACI communicated their recommendations as fast as possible for jurisdictions to consider through a rapid response statement while the full report was being prepared,” said NACI on Wednesday, explaining why the initial call to move to a longer delay between doses came before its full report was ready.

By the end of June, the federal government is anticipating having received a total of 44 million doses of the three currently approved two-dose vaccines from Pfizer-BioNTech, Moderna and AstraZeneca. Shipments of the one-shot Johnson & Johnson vaccine are expected to begin later this month.

The infectious diseases, immunology, pharmacy, epidemiology, and public health experts who make up this advisory body make 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.”

NACI continues to say it will keep monitoring evidence on the effectiveness of a delayed second dose and will adjust its recommendations if needed.

In a separate release, the Council of Chief Medical Officers of Health backed NACI’s guidance.

“Receiving a second vaccine dose as soon as supplies allow, within the recommended interval, remains essential to achieve optimal protection from the two-dose vaccines,” the council wrote.

“We understand that everyone is looking forward to returning to a sense of normalcy… As vaccination rolls out across Canada, it provides us with the opportunity to consider how best we can adapt public health measures, and gradually lift the most restrictive ones,” said the council.