TORONTO -- When a vaccine requires two doses, how should provinces handle their shipments of vaccines -- set aside the second dose and commit to a slower rollout, or deliver shots to as many people as possible and risk a delay in shipments of the second dose?
It’s a question that is preoccupying officials and the public.
As of Wednesday afternoon, more than 83,000 vaccine doses had been administered in Canada, roughly 0.2 per cent of the population.
With the Pfizer-BioNTech vaccine, which was the first to be approved in Canada, the second dose is taken 21 days after the first. Since vaccine doses started to be given out in mid-December, the soonest that those people would start receiving their second shots is early next week.
The first shipments of the Moderna vaccine arrived in Canada last Thursday. Those who receive this vaccine will get their second dose around a month after the first.
SHOULD PROVINCES HOLD ONTO THE SECOND DOSE?
Both Moderna and Pfizer require two doses of the vaccine to ensure immunity, a system which has spurred two different strategies for the vaccine rollout.
Some provinces, such as British Columbia and Manitoba, have chosen to give as many people their first shot as possible -- using up their first shipments of vaccines to give a greater number of people partial protection and relying on further shipments coming within the waiting period to make up the second shots those people will require.
Other provinces, including Ontario and Quebec, have chosen to do the math to set aside the second dose for each person that they vaccinate, in order to ensure that those people will get that second dose even in the event of a delay in further shipments of the vaccine.
Alberta is one province that held back doses at first, but pledged this week to reverse the policy after falling far short of their goal to deliver 29,000 shots by the end of the year.
Federal officials were asked in Ottawa today if they intend to publish guidelines on how provinces should handle the vaccine rollouts. Intergovernmental Affairs Minister Dominic LeBlanc emphasized that “provinces have the responsibility of vaccinating their own populations, and as soon as possible.”
Major General Dany Fortin, who is overseeing the process of delivering vaccines to jurisdictions across the country, said Wednesday that “vaccine producers do recommend that we keep a second dose,” adding that this was the advice given when the additional shipments coming in January had not been confirmed.
“Now, things are confirmed, we will be receiving our shipments,” he said.
However, he pointed out that “provinces and territories do have to manage possible risks” regarding the timing of shipments.
“When it comes to our level of confidence in shipments, well, we have a lot of remote regions, there could be issues with winter weather and other logistical challenges,” Fortin said. “A given province or territory might decide to vaccinate a higher number of people now and then use a future shipment as second doses for those same people. We respect provincial and territorial responsibilities, and that is a provincial and territorial responsibility.”
WHICH STRATEGY IS BEST?
Opinions vary, even among experts.
Dr. Zain Chagla, an infectious disease specialist with McMaster University, explained the thinking behind each strategy to CTVNews.ca last week, saying B.C.’s strategy of not holding back the second dose is based on a trust in the supply chain.
“[B.C.’s thinking is] we’re fine. We’ll get the doses,” he said. “Let’s just get more people vaccinated to provide some safety. In the worst case scenario, we can delay it by a couple of weeks. It’s not the end of the world.”
Ontario’s approach of holding back the second dose is more “careful,” he said, especially in anticipation of possible manufacturing delays. He also notes this approach could be more prudent in the long run.
"In the grand context, this is a marathon and not a sprint," Chagla said. "We should probably be focusing on making sure that the people who are vaccinated have the most robust vaccine series rather than just saying let’s spray it out as much as possible and hope that we get the second dose.”
However, some experts point out that the partial protection offered by even one dose of these vaccines could make a serious difference in slowing down the transmission of the virus if more people are given their first shot quickly.
“Many of us believe that we should be giving one dose to everyone rather than keeping a second dose behind,” Anna Banerji, an infectious disease specialist, told CTV News Channel on Monday. “That’s how we’re going to get this under control.”
The Pfizer-BioNTech vaccine efficacy is 52 per cent after just one shot, with protective effects kicking in around 12 days after receiving the shot. That efficacy rose to 95 per cent seven days after the second dose.
This means that those who have received only one shot can still feasibly get COVID-19 -- but that the likelihood has significantly decreased.
The likelihood of contracting COVID-19 is even smaller after one dose of the Moderna vaccine. The vaccine demonstrated an 80 per cent efficacy after just one dose in Moderna’s clinical trials -- but as all of the participants received a second shot a month after the first, at which point the efficacy rose to 94 per cent, there is no data on whether or not receiving one shot by itself provides immunity that lasts past 28 days.
NARROWING THE VACCINE TO ONE DOSE ALONE?
The increased efficacy of Moderna’s vaccine based on a single shot has prompted some to suggest we simply forget about the second shot.
Retired Gen. Rick Hillier, the head of Canada’s vaccination program, asked this week if Health Canada could look into the possibility of the Moderna vaccine being delivered in only one dose -- something that health officials at the Public Health Agency of Canada (PHAC) rejected Wednesday.
“From a scientific, public health, medical perspective, it’s all with a two-dose regime, and that’s what Health Canada has approved,” Howard Njoo, Deputy Chief Public Health Officer at PHAC, said Wednesday. “There’s no data there to look at in terms of if there was a one-dose regime, what that would have in terms of an impact on either the duration of immunity or the efficacy over the long-term.”
Dr. Ronald St. John, former and first Director General of the Centre for Emergency Preparedness and Response at PHAC, told CTV News Channel on Wednesday that we need to “trust the science.”
The vaccines currently being approved have gone through the standard three phase process to demonstrate the efficacy and safety of the vaccine, he said, and the results show that it takes two doses to achieve a 94-95 per cent effectiveness.
“One dose might give you 50 per cent, but the person who is vaccinated doesn’t know whether they’re going to be in the 50 per cent protected or 50 per cent unprotected,” he said. “So you may have somebody who feels ‘oh, I’ve been vaccinated, and I’m fine,” but they may still be totally susceptible to the virus.”
