The swift arrival of multiple COVID-19 vaccines has offered hope for the end of the global pandemic, but there's still a question of how long people are protected from the virus after they receive their shots.
An exact timeframe of immunity, which protects against severe outcomes and will likely vary from person to person, won't be clear for some time, experts say. But there's reason to believe those inoculated against COVID-19 could obtain a long-term level of protection.
Steven Kerfoot, an associate professor in the immunology and microbiology department at Western University, says data from past infections and from the vaccines themselves suggest "a perfectly good immune response that will last up to a few years for most people."
"You can't know for sure — there's no test to tell you this will last for 10 years," Kerfoot said. "But there's absolutely no evidence to say immunity is going to disappear in a year."
Experts can get an idea of the longevity of a vaccine's immune response by looking at the protection we get after a natural infection from the same virus.
While some studies have suggested antibodies may disappear relatively quickly after COVID infections, others have found a more lingering immune response.
A study by a research team at the University of Toronto published in October found antibodies remained stable in blood and saliva for at least 115 days after infection. That was the longest time interval measured in the study and could mean antibodies persisted beyond that.
An American study published last week showed antibodies were present for at least eight months.
Jason Kindrachuk, a virologist with the University of Manitoba, expects to see studies detecting antibodies for longer as data stretches further and further back. Right now, he says, our "perspective of long-term is really the last 12 months."
"There's hope that people naturally infected may have immunity beyond that one year timeframe, and may get into multiple years," he said. "But we're starting to get into hypothesis at that point because we don't know."
Even studies suggesting an early drop-off of antibody levels aren't cause for alarm, Kerfoot says.
Antibodies pop up quickly to fight off infection once it sets in and start to disappear steadily after that, he explained. What's left is "a slow reduction over years of specific antibodies, immune cells and memory cells" that can help fight off future infections from the same virus.
"What we're talking about in that case is not necessarily protection from being infected, but protection from severe disease," he said. "From the immune perspective that's just as good."
While the rise of a potentially more transmissible variant of the virus has spurred concern over the vaccines' effectiveness against future strains, Kerfoot doesn't see that as a problem right now.
He also doesn't think we'll need an annual COVID shot similar to the flu vaccine, which is necessary because the influenza virus differs from year to year. A booster may be needed, but he expects that to be years away.
Horacio Bach, an adjunct professor of infectious diseases at UBC, says vaccine development typically takes much longer than it did with COVID, and some level of immune longevity can be established over prolonged clinical trials.
"Once you vaccinate, you have to see these people after one year, two years, to see if they're protected and how they're protected," Bach said.
But Kerfoot says the trial process for most vaccines "never really stops," and there's expectation of continued surveillance as more and more people are inoculated.
He expects that to happen to an even greater degree with the COVID vaccines because of the pandemic urgency.
"For all vaccines, you can't wait a 10-year trial to see if it's going to last 10 years," Kerfoot said. "You see if it produces an effective response and if it's safe ... and then you approve it."
Kindrachuk calls vaccine development "a long game," and scientists may continue to develop inoculations with longer immunity profiles over time.
He expects second- and third-generation vaccines "moving through the pipeline," with each potentially offering improvements on the last.
"We don't know yet, but it's something the science is developing," he said. "And it's certainly developing in the right direction."
This report by The Canadian Press was first published Jan. 12, 2021.
Melissa Couto Zuber, The Canadian Press