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Maimonides Geriatric Centre is shown in Montreal on Nov. 29, 2020.Graham Hughes/The Canadian Press

As one of the first people in Canada to receive a COVID-19 vaccine, Mendy Fellig was looking forward to receiving a second shot that would solidify his immunity against a virus that has killed at least 54 of his fellow residents at a Quebec nursing home.

But instead of receiving his booster jab as scheduled in early January, Mr. Fellig, a 43-year-old lawyer with multiple sclerosis, has joined a group from the Maimonides Geriatric Centre threatening legal action against the Quebec government for postponing all second doses until at least 12 weeks after the first – about two months longer than vaccine makers recommend.

“I was really not very happy about it,” Mr. Fellig says, adding he may have turned down the first dose if he had known he wouldn’t receive the second on time.

Mr. Fellig and other early vaccine recipients are caught in the middle of a life-and-death scientific debate about when to inject second doses of coronavirus vaccines. Quebec is one of the few jurisdictions in the world following Britain, a country overrun by a fast-spreading new variant of the coronavirus, in delaying follow-up injections by 12 weeks or more.

With infections surging and not nearly enough shots to go around, the Public Health Agency of Canada’s National Advisory Committee on Immunization (NACI) is planning to release formal recommendations on postponing second shots as early as Monday.

Meanwhile, Public Services and Procurement Minister Anita Anand warned on Friday that provinces that deviate from the vaccine makers’ recommended timelines could hinder Ottawa’s efforts to negotiate for more and faster shipments.

Experts advising the Quebec government say that offering the partial protection of a first dose to as many people as possible as soon as possible will save the most lives. Other experts, including scientists at the U.S. Food and Drug Administration, argue it’s best to stick to the evidence when rolling out new vaccines in the midst of a raging pandemic.

There’s a risk the immunity conferred by the first dose could drop off faster than expected, or that encountering people with incomplete immunizations could prompt the virus to mutate to evade the vaccines.

Medical epidemiologist Gaston De Serres says those theoretical risks pale against the known risks of COVID-19, especially in parts of Canada grappling with a frightening postholiday surge in cases. He co-authored a report recommending a longer interval between doses on behalf of the immunization committee at Quebec’s national public-health institute, known by the French abbreviation INSPQ.

“We’re facing a crisis,” Dr. De Serres said. “We’re facing a period where the incidence is so high, the number of hospitalizations is so high, that we need to do something now. Not in six months. It’s now that people are dying of this disease.”

The first two vaccines to be approved in Canada, made by Pfizer-BioNTech and Moderna, are supposed to be given in two doses separated by 21 and 28 days, respectively. Those were the intervals used in clinical trials that found both vaccines, which use new messenger RNA technology, to be about 95-per-cent efficacious.

There is no evidence about how well the vaccines work if the second injection is put off, spokespeople for both companies told The Globe and Mail this week. The vaccine makers strongly favour sticking to the schedule.

However, data from both companies’ trials suggest the efficacy of the first shots could be as high as 80 per cent to 90 per cent toward the end of the interval between doses.

When the first Pfizer-BioNTech vaccines were shipped last month, the jurisdictions that received them – including some Canadian provinces – planned to keep half in freezers to serve as second shots, as the vaccine makers recommended.

Most have reversed that stand, including Ontario, which is now planning to inject initial supplies swiftly and rely on future deliveries for booster shots they still intend to give out as close to the three or four-week mark as possible. Premier Doug Ford appeared at a photo-op this week alongside the first personal-support worker in the province to receive a second dose of the Pfizer-BioNTech vaccine on schedule.

British Columbia, meanwhile, is planning a slight delay, with second injections coming two weeks late, at the 35-day mark.

U.S. president-elect Joe Biden’s transition team announced Friday that Mr. Biden intends to distribute all available doses as soon as he takes office, reversing the Trump administration’s policy of keeping second doses in reserve.

Ontario’s COVID-19 science table released a paper this week that projected the province would avert significantly more cases of COVID-19 if it rolled out its first allotments of vaccine right away; if Ontario stretched the interval between doses to 35 or 50 days, even more cases of COVID-19 would be prevented, the modelling work shows.

“Mathematical modelling has shown that if you are able to protect more people quickly when the community transmission is high – even though the efficacy might be lower – you’re still going to be have benefits in terms of hospitalization and mortality,” says NACI chair Caroline Quach-Thanh, an infectious diseases physician and epidemiologist at Montreal’s Sainte-Justine Hospital. (She spoke on her own behalf, not on behalf of NACI.)

When it comes to two-dose immunizations for other viruses, Dr. Quach-Thanh says increasing the time between the prime and booster shots actually improves their performance. “It’s not a problem with other vaccines,” she said. “Of course, this vaccine is a new technology.”

The mRNA vaccines aren’t just new, they’re also being deployed while the coronavirus is circulating wildly. “That mix is a dangerous mix,” says McMaster University immunologist Charu Kaushic, a member of Canada’s COVID-19 immunity task force, “because the virus will have a chance to mutate, potentially, in people who have narrowing immune responses.”

Dr. Kaushic is also worried that changing the dosing schedule could undermine public trust in the new mRNA vaccines.

“If there are any problems and breakthrough infections,” she says, “the whole platform would get a bad reputation.”

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