Vaccine panel's call for longer dosage intervals is based on 'real-world' evidence, says health official

One of Canada's top public health officials sought to reassure Canadians today that a recommendation from a federal vaccine advisory committee to stretch out the time between COVID-19 vaccine doses is a sound one.

Yesterday, the National Advisory Committee on Immunization (NACI) recommended that the maximum interval between the first and second doses of all three COVID-19 vaccines approved for use in Canada should increase to four months due to limited supplies.

Deputy Chief Public Health Officer Dr. Howard Njoo said the advice is based on real-world data that shows doing so would lead to more people being protected from COVID-19 in a shorter time period.

"This recommendation is based on clinical trial reports and emerging real-world evidence from around the world. Data shows that several weeks after being administered, first doses of vaccines provide highly effective protection against symptomatic disease, hospitalization and death," Njoo told a technical briefing today.

Njoo's comments appeared to be addressing the confusion created by the fact that NACI's recommendation conflicts with those issued by Health Canada when it granted regulatory approvals for the Pfizer-BioNTech, Moderna and AstraZeneca vaccines.

Regulatory documents provided by Health Canada upon approval of each vaccine state that the second dose of the Pfizer-BioNTech should be taken three weeks after the first, the second Moderna shot should come four weeks after the first, and the second AstraZeneca dose should be delivered between four and 12 weeks after the first. All of those recommendations are in line with the product monograph provided by the manufacturers.

Deputy Chief Public Health Officer Dr. Howard Njoo comments on the National Advisory Committee of Immunization's recommendation that jurisdictions with limited supplies of COVID-19 vaccines delay administering second doses for up to four months.

But Njoo said the discrepancy is due to the fact that Health Canada is a regulator and NACI is an advisory body made up of medical experts.

"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.

"What we expect is that NACI recommendations will complement — not mirror — those of Health Canada."

NACI said stretching the dosing interval to four months would allow up to 80 per cent of Canadians over the age of 16 to receive a single dose of COVID-19 vaccine by the end of June, without compromising vaccine effectiveness.

"While studies have not yet collected four months of data on vaccine effectiveness after the first dose, the first two months of real world effectiveness are showing sustained high levels of protection," NACI said.

The issue burst into the open on Monday when B.C.'s Provincial Health Officer Dr. Bonnie Henry announced that the province would be extending the interval between doses of the Moderna, Pfizer and Oxford-AstraZeneca vaccines to 16 weeks.

Some medical experts questioned that decision. Canada's chief science adviser, Mona Nemer, said doing so without proper clinical trials amounts to a "population level experiment."

Despite the warning, several provinces followed Henry's lead and even more have indicated they intend to stretch the dosage interval.

Dr. Supriya Sharma, Health Canada's chief medical adviser, said expert advice will continue to change as more data becomes available from ongoing mass vaccination campaigns, and she urged provinces and territories to consider recommendations and evidence from both bodies when making decisions about their vaccine strategies.

"The messaging would be simpler if we had one set of data and we had one message and it never changed, but that's not what science does," said Sharma.

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