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Vaccines are supposed to be our way out of the COVID-19 pandemic, but getting people vaccinated has proven to be a difficult task in many countries. In the race to get ahead of soaring infection rates, governments have had to make some tough decisions about whether to delay doses, mix vaccines or speed up safety checks. And there’s growing concern among some scientists that new variants of the virus could elude vaccines. Here are some of the issues health experts have had to tackle.



Barbara Shields-Johnson, director of Nursing Services at Chicago's Loretto Hospital, gets her second and final dose of the Pfizer-BioNTech COVID-19 vaccine on Jan. 5.

Ashlee Rezin Garcia/Chicago Sun-Times via AP

Should the second dose be delayed to get more people vaccinated?

All of the vaccines currently in use – from Pfizer-BioNTech, Oxford-AstraZeneca and Moderna – require two doses up to 28 days apart. The first shot instructs the immune system to recognize the virus and the second provides a boost to reinforce the message.

Britain has decided to delay the second dose by 12 weeks to quickly inoculate as many vulnerable people as possible. Health officials have defended the decision by citing data that show that the first shot provides up to 90-per-cent protection. They also say the rapid spread of a new variant of the virus has left them with little choice.

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Many scientists have questioned the move and so far no other country has followed Britain’s lead. Denmark has opted for a six-week delay and Germany considered waiting 12 weeks but dropped the idea. The Public Health Agency of Canada is sticking to the prescribed dosing schedule but health officials in Quebec have begun using vials that had been stored for second doses. The National Advisory Committee on Immunization, NACI, is also looking into the timing of the doses.

The fear among scientists is that Britain’s decision was based on assumption and not fact. None of the vaccine trials examined the effect of delaying the second dose in detail. Instead, health officials in Britain have extrapolated some of the data and concluded that the Pfizer-BioNTech and Oxford-AstraZeneca vaccines were up to 90-per-cent effective after the first dose. Moderna’s is believed to be 80-per-cent effective after the initial inoculation.

Changing the dosing schedule of the Pfizer-BioNTech and Moderna vaccines – which have been approved in Canada – could be especially risky, scientists say, because they use a novel genetic technology called messenger RNA, which hasn’t been tested before. “The time interval for a mRNA booster may be very critical for getting the best sustained immune response,” a group of scientists said in a commentary in the British Medical Journal. “Extending a second injection out to beyond 28 days could compromise vaccine efficacy.”

Pfizer and BioNTech have also cautioned against changing the dosing schedule and said there was “no data to demonstrate that protection after the first dose is sustained after 21 days.”

British health officials insist that the benefits of vaccinating more people are too important. “This is a sensible balance of risk,” said Chris Whitty, England’s Chief Medical Officer.

Are the vaccines interchangeable?

Jasna Stojanovski and Melissa Hyde, registered pharmacy technicians at St. Michael's Hospital in Toronto, prepare syringes with COVID-19 vaccine.

Melissa Tait / The Globe and Mail

Health officials have come to different conclusions about whether it’s okay to mix vaccines – giving a first dose of one followed by a second dose of another.

Canada’s NACI said that “currently, no data exist on the interchangeability of COVID-19 vaccines.” It has recommended that every effort should be made to use the same vaccine but the committee noted that the Pfizer-BioNTech and Moderna vaccines use similar technology. “If the vaccine product used for a previously received dose is not known, or not available, attempts should be made to complete the vaccine series with a similar type of COVID-19 vaccine e.g. mRNA vaccine,” it said.

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The U.S. Centers for Disease Control and Prevention has recommended against mixing vaccines. “These mRNA COVID-19 vaccines are not interchangeable with each other or with other COVID-19 vaccine products,” the agency said in its recent guidance. “The safety and efficacy of a mixed-product series have not been evaluated.” Germany’s health minister has also ruled out mixing vaccines.

Health officials in Britain have said that there may be “extremely rare occasions” when vaccines could be mixed. For example, if the same vaccine wasn’t available or the vaccine used in the first shot was unknown, “it is reasonable to offer one dose of the locally available product to complete the schedule,” said Public Health England. “This option is preferred if the individual is likely to be at immediate high risk or is considered unlikely to attend again.”

Some scientists have said that mixing vaccines is the next step in the fight against COVID-19. AstraZeneca has announced plans to test a combination of doses of its vaccine with Russia’s Sputnik V, which both use a weakened version of a common cold virus that causes infections in chimpanzees.

“This is the logical next step in vaccine development for COVID-19 as priming with one type of vaccine and boosting with another is a commonly used strategy for increasing the level and duration of efficacy against infectious disease,” said Helen Fletcher, professor of immunology at the London School of Hygiene and Tropical Medicine.

Is it okay to squeeze an extra dose out of each vial?

A health-care worker holds a vial of AstraZeneca vaccine at the Pentland Medical Practice in Currie, Scotland, on Jan. 7.

Russell Cheyne/Reuters

The Pfizer-BioNTech and Oxford-AstraZeneca vaccines were made to come in vials that contain enough for five doses. Moderna’s vials have 10 doses.

However, once the vaccines rolled out in Britain and the U.S., clinicians quickly discovered that there was often enough left over for an extra dose and sometimes even two. At first, many health care workers threw away the extra vaccine because they didn’t have authorization to go beyond the manufacturer’s specifications.

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Health regulators in both countries have now given approval to squeeze out an additional shot whenever possible and BioNTech has asked European Union officials for a similar change in directive. Britain has said that the extra dose should be given to front-line hospital staff even if they are not immediately slated to get vaccinated.

Health Canada has also said it had no objections to health care professionals “drawing up an additional dose or two from each vial, where possible.”

Health officials say getting an extra dose out of each vial can increase the number of people vaccinated by up to 20 per cent. But they’ve cautioned that if a full extra dose can’t be extracted, the remainder must be scrapped.

Paramedics assess a Covid-19 patient in the Johannesburg suburb of Lenasia on Jan. 4. South Africa was hit with a more contagious variant of COVID-19.

MICHELE SPATARI/AFP via Getty Images

Do the vaccines work against new variants found in Britain and South Africa?

Scientists have always warned that the virus that causes COVID-19 will mutate repeatedly and so far they have tracked thousands of variations.

Researchers say the variants found recently in Britain and South Africa have been especially significant because they involved multiple genetic changes to how the virus attaches to human cells. That is believed to have made them more contagious. Studies in Britain have found that the U.K. variant, known as B.1.1.7, is up to 70-per-cent more contagious.

The rapid spread of both variants has raised concerns about whether the vaccines will be effective. Julian Tang, a virologist at the University of Leicester, said the two variants have similar modifications that change where the virus binds to human cells and where the vaccine-induced antibodies bind to the virus.

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However, he added that the South African variant, called 501Y.V2, contains two more mutations that also affect how the virus binds. “These two additional mutations may interfere more with vaccine effectiveness in the South African variant than in the U.K. variant,” he said. Dr. Tang added that this didn’t necessarily mean the vaccines wouldn’t work at all, but they could be less effective.

Most scientists believe the current vaccines will provide sufficient protection against the variants. This week Pfizer-BioNTech announced early findings from a study that showed their vaccine was effective, although the company said more testing was needed. Even if the vaccines don’t work, scientists say altering them isn’t complicated and would take a few months.

Which countries have done the most vaccinations?

An Israeli military paramedic prepares a Pfizer-BioNTech dose to be administered to elderly people at a medical center in Ashdod on Jan. 7.

Tsafrir Abayov/The Associated Press

So far Israel is far ahead in terms of rolling out a vaccination program. Figures compiled by Oxford University’s Our World in Data project show that Israel has administered 19.55 vaccine doses for every 100 people as of Jan. 7. That compared with 1.91 in Britain, 1.79 in the U.S. and 0.62 in Canada.

Israel negotiated deals for the Pfizer-BioNTech early on in the pandemic and since launching its vaccination drive on Dec. 20, the country has been administering 150,000 shots per day. Officials have set up vaccination centres in stadiums, parking lots and school playgrounds which are open from 8 a.m. to 10 p.m.

Ramping up a vaccine program is challenging. The Pfizer-BioNTech and Moderna vaccines must be stored at -70C, which complicates logistics. Vials can be kept in a regular refrigerator for up to five days but they must be used within six hours once removed from the fridge. The Oxford-AstraZeneca vaccine is easier to administer since it can be stored in normal fridges for months.

Britain is launching an ambitious effort to vaccinate care home residents, hospital staff and everyone over the age of 70 by mid-February, or roughly 15 million people. That means amping up vaccinations from around 300,000 per week to two million. Health officials plan to administer the doses through a network of 1,500 hospitals, doctors’ offices, pharmacies and vaccine centres in sports stadiums. Roughly 80,000 health care workers and volunteers will be trained to administer the jabs.

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Public health experts say the timetable is ambitious and they point to a number of potential pitfalls. The manufacturers have promised to make enough vaccine to meet the timetable but each batch has to be inspected by regulators, which can take up to 20 days. There’s also a growing shortage of vials, which could slow down production. Training volunteers takes time as well, and there have been concerns that the process involves reams of unnecessary paperwork, including assurances that every volunteer has been trained in fire safety.

Will the vaccines be available in all countries?

A mural encouraging face masks, including an Arabic-language message reading 'protect yourself,' is shown on the main road of Nusseirat refugee camp in the central Gaza Strip.

Adel Hana/The Associated Press

There have been persistent concerns throughout the pandemic that wealthy countries will hoard the vaccines.

To help ensure there’s equitable distribution to all countries, especially the poorest, an alliance called COVAX has been formed by the United Nations. A total of 172 countries have joined along with a coalition called Gavi which includes the World Health Organization, the World Bank, the Bill and Melinda Gates Foundation and several pharmaceutical companies.

COVAX has made arrangements to distribute two billion doses of COVID-19 vaccines to wide range of countries this year. The program has also raised US$6-billion of the US$7-billion it needed in 2021 for COVAX AMC, which aims to get vaccines to 92 of the world’s poorest countries. Kate O’Brien, the WHO’s immunization director, said this week that the deliveries will start in late January or early February.

Canada has been among the largest donors to COVAX AMC and the government recently pledged $75-million.

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