Could a vaccine wipe out COVID-19 or will protection be short-term? That's the 'million dollar question'

In 1910, a young girl was taken to a hospital in Hamilton, Ont. with a suspected case of rabies.

It wasn't until after her death that clinicians discovered what was actually wrong: She'd somehow contracted polio, marking the grim start of Canada's first outbreak of the contagious viral illness, which wound up paralyzing — or killing — tens of thousands of Canadians.

In 1953 alone, the year the disease peaked, 9,000 children across the country were infected, and 500 died.

But after polio vaccines were rolled out widely that same decade, the virus quickly started to disappear. In 1994, four decades later, Canada was declared polio-free.

Could a vaccine for the new coronavirus lead to a similar outcome?

That's the best-case scenario — but it's far from certain. 

Even amid unprecedented collaboration, with researchers around the world scrambling to develop at least one safe, successful option, there's still lots to learn about SARS‑CoV‑2, a virus that's been spreading among humans for only a few months. 

Would a vaccine for the new coronavirus wind up offering long-lasting immunity, potentially wiping out COVID-19 across Canada? Or will the virus prove to be a shape-shifter, mutating quickly enough that people need annual vaccines like those for seasonal strains of influenza?

"We don't yet know the answers to those questions," says Dr. Mary Carol Jennings, a public health physician and vaccine scientist at Johns Hopkins University's Bloomberg School of Public Health. "The answers will help us imagine what it would look like."

Those conclusions will also shed light on whether COVID-19 could one day fade out from public consciousness — or remain a threat for decades to come.

Dozens of vaccines in development

RIght now, dozens of potential SARS‑CoV‑2 vaccines are being developed in countries across the globe, including here in Canada, with some as far along as human trials as companies race to release options years ahead of typical timelines.

Infectious disease expert Dr. Matthew Miller, an associate professor at McMaster University's department of biochemistry and biomedical sciences, says most of the contenders closest to the finish line focus on the same area of the virus: The spike protein.

Those exterior spikes are what put the "corona" — or crown formation — in the virus's name. They're also what it uses to latch on to human cells, ultimately breaking through their outer membranes to hijack their machinery in order to replicate.

Each cone-shaped spike protein is multi-layered, notes Halifax-based pediatric infectious disease physician Joanne Langley, a vaccine researcher at the Canadian Centre for Vaccinology who's helping lead clinical trials for potential SARS‑CoV‑2 vaccines through the Canadian Immunization Research Network.

"If you were looking at, say, a rose and you were a bee, and you could go in between the petals — it has all those shapes and structures. It's not just one flat thing," she explains.

SARS‑CoV‑2 spike protein

To create long-lasting protection, researchers need to pinpoint a piece of that structure that's likely to remain stable over time, then isolate and de-activate it, which could require an old-school method like using a chemically-killed virus, or genetically modifying viral information so it can't infect humans.

Once someone is given the vaccine containing that key viral code, their body can memorize how to fight back against the threat whenever it returns, like an army learning intel about the best way to fend off a particular invader. 

Take the measles vaccine, for example. Like all viruses, it does mutate over time. "The vaccine we have is 70 years old," Jennings notes, but it's still effective since it "targets a stable part of the virus."

On the flip side, if a vaccine targets part of the spike protein that winds up evolving rapidly, then the immune system — that internal army — is stuck with outdated information, leaving it vulnerable to the changing threat.

COVID-19 could be 'long-term battle'

So how will researchers figure out how long a successful vaccine will keep people immune to COVID-19, and what form it will take?

That's the "million dollar question," Jennings says.

Knowing for sure how long immunity will last requires following vaccine test subjects over time. Say researchers are hoping for a full year of protection. That means, at a basic level, you have to test the vaccine, wait a year, and test subjects again to see if they're still able to fight off the antigen.

Given the pressing need for a successful vaccine, amid a global death toll of a quarter-million and counting, Langley says there's no room for that kind of delay.

Instead, research teams need to make predictions based on how robust the immune response is after 28 days — a much shorter window that still allows enough time for someone's body to recognize the virus, and start producing antibodies to fight it.

Thankfully, this coronavirus seems to remain fairly constant, Langley notes. "It's not like influenza that's shifting and drifting over time, and having radical changes," she says. "But we don't know for sure."

Annual flu vaccines often wind up being out of date, with researchers trying to predict which strains will emerge as the most powerful months down the line.

It's also challenging to manage widespread yearly vaccination programs, says the University of Toronto's Dr. Natasha Crowcroft, a specialist in infectious diseases and immunization.

She agrees the early research shows a SARS-CoV-2 vaccine likely won't require that kind of seasonal uptake to protect people, though it could be similar to other long-lasting vaccines — including those for tetanus, measles, mumps, and rubella — which require more than one dose.

"My expert opinion is that it will be something intermediate," echoes Miller, adding it probably won't require annual revaccination, but more likely booster shots at certain intervals.

Given the early research into how this virus operates, wiping out COVID-19 is "plausible," Crowcroft says. With a fairly low reproductive rate, the new coronavirus wouldn't require every single person to be immunized in order to produce widespread protection, she explains.

At the same time, that scenario relies on the vaccine's long-term success level on an individual basis — an outcome we likely won't know for years until options are fully tested, mass-produced, and provided to the public.

With so much uncertainty, Miller warns the new coronavirus — or other similar, undiscovered strains — could wind up causing seasonal infections in Canada long after this pandemic, unlike polio which largely faded into the country's history books.

"This is much more likely to be a long-term battle for us," he says. "It's unlikely that we're going to be able to eradicate this thing."