Dr. Henry defends delaying of second doses of COVID-19 vaccine

Henry defends delayed dose

UPDATE 5:30 p.m.

Provincial health officer Dr. Bonnie Henry defended Tuesday her decision to delay second doses of the coronavirus vaccine to up to four months in an effort to get more first doses to more people.

Henry came under fire Monday from federal chief science advisor Dr. Mona Nemer, who said the decision amounted to a “population-level experiment,” suggesting provinces stick to what the vaccine manufacturers have recommended — three to four weeks.

Henry said Nemer’s remarks were “a little bit unfortunate,” as she “obviously was not involved in some of these discussions and decision making and perhaps didn't understand the context that this decision was made in.”

Henry said B.C. is “following the science of vaccines,” referring to scientific papers published locally and abroad. Many of those studies have come out of the U.K., which is also delaying second doses.

“This makes sense for us, knowing that it is a critical time right now with the limited vaccines that we have in the coming weeks,” Henry said.

"Our focus is on maximizing the number of people who are benefiting from that very high, real world protection that we are seeing from the first dose of vaccine in B.C.”

She noted the clinical trials used to develop the vaccines were using a short interval to expedite their approval, but in many cases, vaccines perform better when booster doses are spread out.

“We know from immunology that the booster dose, the timing of the booster dose can sometimes confer additional benefits,” she said, pointing to vaccination against Hepatitis A and B.

As for the United States decision to stick with a two-dose regimen, Henry suggested it is not a fair comparison as the U.S. has a shortage of vaccine availability like Canada has.

Dr. Danuta Skowronski, a B.C. Centre for Disease Control epidemiology lead whose work underpinned the province's plan, said Pfizer-BioNTech underestimated the efficacy of its first dose in its submissions to the U.S. Food and Drug Administration.

Skowronski said the company included data from the first two weeks after trial participants received the shot, a time when vaccines typically aren't effective. When she and her colleagues adjusted the data, they found it was 92 per cent effective, similar to the Moderna vaccine.

She said B.C.'s plan was based on the basic principles of vaccine science. The protection from a first dose of vaccine does not suddenly disappear, it gradually wanes over time, and scientists are typically more concerned about providing a second dose too soon rather than too late, she said.

"I think if the public had a chance to hear and to understand that, they would say, 'OK, this is not messing around. This is really managing risk in a way that maximizes protection to as many Canadians as possible.'"


The B.C. government’s announcement that it will significantly increase the spacing between the two doses of the coronavirus vaccine is being met with skepticism from some in the science community.

Provincial health officer Dr. Bonnie Henry said moving the vaccine window between the two doses to four months, up from the previous 42 days, will free up more first doses for more people. The government pointed to plummeting cases and deaths in the long-term senior care system as proof of better-than-expected efficiency of just a single dose.

But Canada’s chief science advisor Dr. Mona Nemer says the move amounts to a “population-level experiment.”

Speaking to the CBC on Monday, Nemer said all the clinical trials related to the Pfizer and Moderna vaccines are based on the two doses being given 3-4 weeks apart, not four months.

“I think it’s really important that we stick with the data and with the great science that gave us these vaccines and not tinker with it,” she told the CBC, adding a clinical trial testing the efficiency of spreading out the doses should be done before rolling it out to the general public.

“Perhaps we will find out that we can space these different doses, but for now, we simply don’t have enough data that tells us this is an effective strategy,” she said, noting mutated COVID-19 variants are another risk factor.

“I think that partial immunity is something that people need to be very wary of and it is probably best to just vaccinate as recommended and as studied for now.”

“I think they may be carrying out a large clinical trial,” she said, adding “it amounts to a basically a population level experiment.”

United States top infectious-disease expert Dr. Anthony Fauci said Monday the country will stick with a two-dose regimen. The United Kingdom, however, has also opted to delay the time between the two doses.

Fauci told the Washington Post both approaches are “quite reasonable.”

But Fauci said the science right now doesn’t support delaying a second dose, as a single-shot could leave people vulnerable to variants.

“You don’t know how durable that protection is,” he said.

The Ontario government said Tuesday it is waiting on guidance from the National Advisory Committee on Immunization before making any decision on delaying second doses.

Dr. Henry said Monday she was expecting a statement from the committee that would align with B.C.’s decision.

She said the decision was based on local and international evidence that shows the first dose of Pfizer-BioNTech and Moderna vaccines provides "miraculous" 90 per cent protection from the virus.

Alberto Martin, a University of Toronto immunology professor, says a published clinical trial showed the first dose of the Pfizer-BioNTech vaccine provided 60 per cent protection, but B.C. may have access to new or unpublished data.

He says there is "obviously some concern" about B.C.'s plan because he is not aware of any clinical trial that examined a four-month gap between doses, but difficult times — when the vaccine supply is so limited — require drastic measures.

with files from the Canadian Press

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