![]() ![]() "After looking at it from all of these angles, and given that we are in a situation of limited supply, the committee came to a strong consensus that we recommend the interval to be extended to four months." Shelley Deeks, vice-chair of NACI and a lead author of the recommendations, said in an interview. "It's shown us really good vaccine effectiveness two months after receipt of the first dose and that the effectiveness isn't decreasing over time," Dr. that showed "good effectiveness" of between 70 and 80 per cent from a single dose of the vaccines "for up to two months in some studies."īut it also makes clear that these studies haven't yet collected four months of data on the long-term effectiveness of a single dose, meaning NACI is betting on the "high levels of protection" shown so far. NACI says its decision to delay second doses is based on emerging real-world data from Quebec, B.C., Israel, the U.K. Canada's chief science adviser issues warning about B.C.'s 'experiment' with vaccine timingīut aside from a vague reference to "real-world effectiveness" from Canada and other countries in NACI's recommendations, little evidence has been communicated to Canadians to convince them that the change in vaccine rollout strategy is the right move."It did not reflect the careful risk-benefit analysis that went into this decision, and frankly, that is a science and an art to be able to do that." ![]() "The comment from the chief science adviser was most unfortunate," said Skowronski. NACI says if second doses are stretched to four months across the country starting this month, close to 80 per cent of Canadians over 16 could get at least one shot of the Pfizer-BioNTech or Moderna vaccine by the end of June.īut Canada's chief science adviser, Mona Nemer, says the decision to delay doses amounted to a " population level experiment." Some scientists say we are venturing into uncharted waters. No other country in the world has delayed second doses up to four months, and there is no evidence yet on the long-term effect it could have on immunity to COVID-19. ![]() Ontario, Quebec, Alberta, Manitoba and Newfoundland and Labrador quickly followed suit.Ĭanada is now an outlier in the global vaccination rollout. announced it would be delaying second doses earlier this week. The finding led the National Advisory Committee on Immunization (NACI) to change the recommended time between doses of COVID-19 vaccines from three weeks to an unprecedented four months.ī.C. "What we found was that they were underestimating the efficacy of the first dose, and rather than the efficacy being 52 per cent, it was actually 92 per cent," she said. She told CBC News vaccines are never expected to protect "instantaneously," and that there is always a "grace period" of a couple of weeks that factors into vaccine effectiveness. Centre for Disease Control is in favour of delaying second doses to four months after analyzing the data Pfizer submitted to the U.S. ![]() Pfizer reported an efficacy of 52 per cent for one shot, compared to the more commonly cited 95 per cent after the second.īut Skowronski, who has been working on vaccine effectiveness analyses for more than 15 years, realized the company had included in its analysis the two-week time period immediately after vaccination - before the body's immune response typically kicks in.ĭr. In clinical trials, Pfizer couldn't accurately determine the efficacy of a single shot because participants had already received their second dose after three weeks, and there was no comparative one-dose study done. Food and Drug Administration on the effectiveness of just one dose of its vaccine. The epidemiology lead at the British Columbia Centre for Disease Control realized she could actually "correct" the data Pfizer had submitted to the U.S. If you haven't subscribed yet, you can do that by clicking here.ĭanuta Skowronski was poring over Pfizer-BioNTech vaccine data on a Friday night in mid-December when she had an "aha!" moment. This is an excerpt from Second Opinion, a weekly roundup of health and medical science news emailed to subscribers every Saturday morning. ![]()
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