TORONTO -- Promising early data from COVID-19 vaccine trials may have provided the first sign of an end to the coronavirus pandemic, but much is still unclear.

No vaccine has been approved for use in Canada. Each shot would come with its own logistical barriers. Plus, Canada must wait for shipments from vaccine-producing countries who will inoculate their own citizens first. While Health Canada could be just weeks away from approving Pfizer, Moderna or AstraZeneca vaccine candidates for use in Canada, whether or not one of them spells the beginning of the end and a return to normal remains to be seen. Meanwhile, the latest federal modelling data suggests the second wave of the pandemic could get worse long before a vaccine rolls out across the country. readers submitted their burning questions about COVID-19 immunization and we posed them to infectious disease experts Drs. Isaac Bogoch, Zain Chagla and Sumon Chakrabarti, and other specialists. Here’s what they said. Note: Questions have been edited and condensed for clarity.

As with other aspects of the COVID-19 vaccine process, the approval process has been sped up, said Chagla. Normally, pharmaceutical companies would send completed data sets to Health Canada for approval. Now, analysis of data that would typically be under embargo at this stage is happening in “real time,” he said.

U.S. health officials are expected to meet on Dec. 10 to determine emergency authorization for the Pfizer vaccine candidate, in which case distribution could begin on Dec. 11. Chagla doesn’t expect Canada to take much longer for the approval process, and thinks a vaccine could “start drizzling in at the end of the year.”

“I don’t think Canada is going to let themselves fall that far behind, noting that hopefully most of that data or some of that data is already being fed back to Health Canada right now and it’s really just crossing the T’s and dotting the I’s,” he said. “This is a global emergency that’s shutting down society and relatively so, this is probably the biggest intervention to date that might actually reduce some of the burden in our communities.”

The Canadian government assembled a team of experts and officials months ago to prepare for vaccine rollout, including logistics and prioritization. From an operations standpoint, a Canadian military general is heading the rollout. From a prioritization standpoint, the National Advisory Committee on Immunization (NACI), a long-established body that includes public health, infectious disease, and immunization policy experts, created a vaccine prioritization framework, released in early November. The framework determined that people and staff at long-term care facilities should be immunized first, then other health care workers and vulnerable populations, and finally the general population.

It’s possible that vaccination could be required in certain education, health care and travel circumstances, said Chagla, and there is precedent for it.

In parts of South America and Africa, travellers are required to present a “yellow fever vaccination certificate” to prove they are immune from the virus and won’t set off an outbreak. In Canadian schools, some provinces require children and adolescents to be immunized from a variety of illnesses before they can attend school, unless they have a medical exemption.

“I think you’re going to see some fairly forward-facing industries like travel industries, health care, schools, where this is probably going to be part of the mandate,” said Chagla, noting that mandatory vaccinations get “dicey” when it comes to employment law.

While no one can be forced to get an eventual COVID-19 vaccine, ethicists have urged for more clarity around what the rollout of vaccines will mean, including for millions of people who may choose not to get one.

“That is an ethical concern because what will likely happen to people within that group is more and more opportunities may slowly be shut off to them,” Kerry Bowman, a bioethicist and assistant professor at the University of Toronto’s faculty of medicine, told CTV National News.

Common side-effects will have already been identified since most adverse events associated with vaccines occur within a day of receiving the shot, said Bogoch, the most common of which is a sore arm.

“There are certain rare vaccine side effects that can occur two to four weeks after vaccination. They’re not very common at all,” he said, adding that early data suggests the Pfizer and Moderna vaccine candidates, which use a relatively new mRNA technology, have not resulted in any notable side effects other than people feeling “fatigued or a little unwell” in the day following vaccination.

The Pfizer and Moderna vaccines are both “messenger RNA” or mRNA vaccines, which is a new kind of vaccine technology that is like “giving an instruction booklet for your cells to make antigens,” said Chakrabarti in a phone interview with last month. In the absence of the coronavirus, a person’s cells would still be programmed to develop the antibodies that fight the virus off.

The AstraZeneca vaccine, developed by Oxford University scientists in England, uses a more well-established approach that introduces a cold virus common in chimpanzees. The vaccine alters the chimp virus, called a modified adenovirus vector, to mimic COVID-19 and thereby produce an immune response in the human body.

Probably not. While study participants represented a wide spectrum of ages and ethnicities, they were also all generally healthy people, said Chagla in a phone interview with in November. In the past, when vaccines for other illnesses rolled out, they may have had strong data from clinical trials too. “But they’re not necessarily as good as patients get more complex, as their medications get more complex and their immune system diseases are more complex,” he said, so defining the efficacy of a vaccine after rollout becomes a difficult task. “More surveillance, more data, once it comes to the market, will probably tell us what the real life efficacy of these vaccines are,” he said. “I would suggest it will probably be a little less than this 95 per cent.”

It’s too early to know. The Pfizer and Moderna vaccines require two doses, separated by two weeks, but the second is not considered a “booster” shot, which are given to prevent immunity from waning.

“We don’t have a clue how long immunity will last,” said Bogoch over the phone with in November. “We’ll have clues about this longer-term after people are vaccinated to see how long immunity will last.”

Booster shots are typically given several years after the first, though children will often receive them earlier to provide a more “robust immune response,” said Chagla. “For most adult vaccinations you have a series [of doses], and things like the pneumonia shot or tetanus shot you do at five, 10-year intervals after getting it just knowing that immunity wanes in some of the older populations,” he said.

The Pfizer, Moderna and AstraZeneca vaccine candidates all have different requirements for transportation and storage. Pfizer’s vaccine needs to be kept at -70 C during those stages to remain effective, but it is not administered into someone’s veins at that temperature, assured Bogoch.

“God, that would suck. You’d get frostbite. That would cause tremendous damage,” he said. “The Pfizer vaccine is stable for about five days in a conventional refrigerator. The Moderna vaccine needs to be stored at -20 C but it’s stable in a refrigerator for about 30 days.”

The AstraZeneca vaccine candidate can be stored between 2 C and 8 C, which experts consider a major logistical advantage for areas of the country that don’t have access to ultra-cold freezers.

The specifics of the rollout are still being developed or have not yet been announced to Canadians, but experts expect there to be a variety of methods by which people will be vaccinated. Where someone lives may determine which vaccine they receive by which method.

“It’s going to depend on what vaccine is locally available, what resources are in that region to actually administer them,” said Chagla, noting the different storage temperatures required of the Pfizer, Moderna and AstraZeneca candidates.

“I think you’re going to see a lot of different models. You’re going to see family doctor models, drive-thru models, hospital models, models where people are going into long-term care facilities and plastering it among patients and staff,” he said. “You might get other ways of administering it, like mass vaccination clinics.”

Recent lessons from the administration of influenza vaccines may be informing how a COVID-19 vaccine is rolled out, said Chagla, who expects there to be less reliance on lining up at local pharmacies.

“We can’t have people standing in long lineups, particularly in the era of COVID-19,” he said. “People getting COVID waiting for a COVID vaccine seems like fairly poor optics in that sense.”

If someone is vaccinated and they come into contact with the virus, one of two things is going to happen, said Bogoch: “You’re either going to get the infection, or you’re not.”

Early data from COVID-19 vaccine trials suggests that the probability of getting the infection is significantly lower in vaccinated people than in unvaccinated people. Similarly, the early data suggests severe illness is also less common in people who are vaccinated.

“It’s extremely important to note that we don’t have the data available, and we're only going by the snippets of data that we do have available,” he added.

Yes. While a minority of people get sick and die from COVID-19, that small group of people can still overwhelm the hospital system, said Chakrabarti.

“Once that happens, there’s a ripple affect that has effects on everybody’s health,” he said, noting cancer screening appointments are cancelled and elective operations are postponed. As of Dec. 1, some of the largest hospitals in Canada are were nearing capacity, threatening widespread cancellations of non-emergency surgeries that would further extend a health care backlog.

While some have suggested protecting the elderly and letting the virus “rip” through society to allow for natural herd immunity, Chakrabarti says it’s very difficult to protect all vulnerable people and the consequences of such a strategy can’t be understated.

“The cost of doing that is that you would overrun hospitals and there would be all sorts of collateral damage,” he said.

Maybe, but it’s unlikely that individual people will get each of the Pfizer, Moderna and AstraZeneca vaccines, or some other combination of vaccines, during the first rollout, said Chakrabarti.

“This stuff will be honed in the coming years as we start to get to know more and more. There is a precedent for using vaccines of slightly different mechanisms to give you a synergistic type of effect,” he said, noting that high-risk populations are inoculated with both pneumonia vaccines on the market for a more powerful affect.

There’s also added benefit to having multiple vaccines on the market, whether or not an individual person receives multiple shots. The differences in the storage requirements alone provide important benefits, particularly to the developing world, noted Chagla.

“Right now it’s just a race to get a vaccine on the market rather than necessarily saying ‘What’s the optimal strategy?’” he said. “As things go on, we’re probably going to get more and more data to say which one is better in kids, which one is better in the elderly, which one is better in certain settings, or with certain medications. That’s the benefit fo having multiple on the market.”

While some experts expect a feeling of “normal” to return at some point next year, a complete return to normal might not come until 2022.

“The rollout of the vaccine is a gargantuan task,” said Chakrabarti. “I do completely expect that things will be back to normal sometime in 2022. I think 2021 will be a gradual and stepwise improvement in our daily lives and the case count.”

Chagla expects people will begin to “step off the break” once the most vulnerable populations are vaccinated in the early months of 2021. Summer could be close to normal, he added. “We’re going to see ‘normal’ starting to show up more and more and more as some of those higher-risk settings get more and more vaccinated,” he said.