CALGARY — Alberta Premier Jason Kenney has repeatedly quoted a figure of 10 per cent of Albertans having a “natural immunity” to COVID-19 — referring to those who have survived an infection and now carry antibodies to the disease.
That 10 per cent number is substantially higher than the number of people that Alberta Health Services lists as having been diagnosed with the illness.
As of April 27, AHS lists 184,840 Albertans as having tested positive for the virus. That works out to approximately 4.3 per cent of Alberta’s population. A spokesperson for AHS says officials believe two to three times as many people have actually acquired COVID-19 than have been discovered through testing.
“We know from previous infectious diseases like influenza, serological studies and reports from other jurisdictions around the world that there are always a significant proportion of individuals exposed to a virus beyond confirmed testing,” said Tom McMillan, Alberta Health’s assistant director of communications in an email reply to CTV News where he cited this article as well as this recent US study.
“Seroprevalence data ranges widely and is still emerging. To be clear: the figure quoted was a preliminary estimate only.”
University of Alberta immunologist Dr. Lynora Saxinger says that 10 per cent estimate is likely on the high side.
“I would be looking at maybe seven or eight per cent of the population having been infected. And we’ve had 25 to 30 per cent of the population receive vaccine,” said Saxinger.
“We still have over two-thirds of our population still susceptible to this infection.”
University of Calgary immunologist Dr. Craig Jenne echoes Saxinger’s concerns, adding people who are relying on infection-acquired immunity also have much less protection than those who have been vaccinated.
“The immunity resulting from natural infection is not better, it is not longer lasting, it is not as broad. So it’s a lower quality immunity than what the current vaccines are offering,” said Jenne. “The other big concern and we had seen this early on is we simply don’t know how long that protection loss and in some people that had more mild symptoms, for example, we can measure a loss of those protective antibodies as early as eight weeks after recovery.”
Saxinger says recovery from a COVID-19 infection should be looked at in a manner similar to a first dose of vaccine – providing limited short term protection but needing a booster to maintain protection.
“You have some protection, it’s likely pretty good for at least three to six months, You can get reinfection after natural infection,” said Saxinger.
“It’s possible that some of the variants might be more likely to re-infect you after you’ve had infection with the original COVID strain.”
Jenne also warns the concept of “herd immunity” is a moving target, saying the number of protected individuals needed to reach it grows as variant strains of the disease become more infectious.
“We know that in general, the more infectious a given pathogen or given virus is, the higher the level to reach herd immunity,” said Jenne.
“So models that were based on viral spread in 2020. In the absence of variants are likely under estimating the amount of immunity we need to stop spread because these new variants are two, to two and a half times more infectious.”
Nonetheless, Alberta’s Chief Medical Officer of Health, Dr. Deena Hinshaw stands by factoring in acquired infections in planning Alberta’s reopeing strategy.
“It has been a part of my advice that we need to consider both of those things, because we know that public health measures and public health restrictions have significant impacts on people,” she said during Tuesday’s regular update.
“And so we need to be considering the big picture when we’re looking at summer planning. However, having said that, again, it’s critical that while we’re looking at that big picture for our planning at an individual level, people need to know that even if they’ve had COVID-19 it does not protect them in the same way as having had a vaccine.”