Experts are raising questions about B.C.’s 16-week interval between vaccine doses just as other Canadian provinces consider a similar approach in order to expand protection amid vaccine shortages.
Canada’s chief science adviser, Mona Nemer, told CBC News on Monday that B.C.’s decision to extend the interval to 16 weeks, or 112 days, amounts to a “population level experiment.”
“I think that it’s possible to do it. But it amounts right now to a basically population level experiment. And I think it needs to be done as we expect clinical trials to be carried out,” Nemer told CBC.
Postmedia News reached out to Nemer for an interview but she declined, referring to her earlier comments.
U.S. infectious disease expert Dr. Anthony Fauci has also said he doesn’t agree with spreading out the intervals between doses, a strategy used in the U.K.
Alberta and Ontario have announced they’re considering following B.C.’s lead and extending the interval to 16 weeks.
B.C. provincial health officer Dr. Bonnie Henry said during a news conference Tuesday that extending the vaccine interval will allow most adults to receive their first jab by July, which will dramatically reduce transmission of the virus, hospitalization and deaths. The move is expected to free up about 70,000 doses.
The more people who are vaccinated with the first dose, Henry said, the sooner restrictions can be lifted on social gatherings and visits to long-term care homes. She pointed to research out of the U.K., Israel and Quebec that has shown one dose of the Pfizer or Moderna vaccine provides up to 90 per cent protection for up to four months.
“We know from the real-world data we don’t need to rely on second doses before we lift these restrictions if we have enough people protected with first doses,” Henry said. “We are now looking at months rather than many, many months before we can reach a level where people have enough protection. There is light ahead and it is getting brighter every day.”
The original recommended interval between doses was 21 days for the Pfizer-BioNTech vaccine and 28 days for the Moderna vaccine. In late January, B.C. announced it was extending the interval to 42 days amid vaccine shortages.
Henry said B.C. is in a very different position from the U.S. because the province has a much more limited supply of the vaccine.
“We still have ongoing transmission in our community in quite a serious way,” she said. “So this makes sense for us … (especially) with the limited amount of vaccine we have in the coming weeks to be able to provide that protection that is safe and long-lasting.”
The National Advisory Committee on Immunization currently recommends an interval of no longer than six weeks but Henry said they will be updating that guidance in light of new research.
In February, a team of Scottish researchers analyzed data from the country’s mass immunization campaign, including more than one million people who had received the Pfizer or AstraZeneca vaccine, and found that a single dose provides protection for about five weeks and then starts to decline.
The study, which hasn’t been peer reviewed or published in a medical paper, found that one dose of the vaccine was about 84 per cent effective at preventing hospitalization but then began to decline, going to 61-per-cent-effective in the sixth week, then 58 per cent after that.
A University of Cambridge study that analyzed COVID-19 tests taken by 8,900 U.K. health-care workers found that asymptomatic coronavirus infections were four times less frequent in those who had received a single dose of the Pfizer vaccine compared with those who hadn’t been vaccinated. The study hasn’t been peer reviewed.
On Tuesday, the province announced two more deaths from COVID-19 and 22 more cases of “variants of concern.” There were 438 total new COVID-19 cases on Monday, for a total of 81,367 confirmed cases since the start of the pandemic.
The majority of positive tests were recorded in the Lower Mainland, with Fraser Health reporting 249 new cases and Vancouver Coastal Health reporting 137.
Henry said a total of 182 variants of concern — 159 cases of the U.K. variant and 23 cases of the South African variant — have been detected in B.C. but only eight of the cases were considered active.
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