TORONTO -- Reinfections of COVID-19 have already occurred in Canada, according to new data, but the way this phenomenon is tracked across the country varies province to province -- something experts say could leave a gap in our understanding of how the virus works.

Exactly how long a person is immune after recovering from COVID-19 is still one of the pandemic’s mysteries. All evidence so far suggests that reinfection is rare, and that second infections are milder.

But with new variants of the novel coronavirus circulating, bringing a potential risk of increased reinfection, it’s a topic that some experts believe we should be investigating more.


According to the Provincial Health Services Authority in British Columbia, the province has had three confirmed cases of reinfection since the start of the pandemic: one in the Vancouver Coastal Health region and two in the Fraser Health Authority region.

The health authority told by email that the first confirmed reinfection was in July, and that two more cases followed in October and November.

These appear to be the first confirmed cases of reinfection for Canada, although more information on the cases was not immediately available.

A potential case of reinfection in Nova Scotia made headlines this fall when it was announced, but according to officials, it still hasn’t been confirmed.

“In September, we announced an individual who tested positive for COVID-19 after previously recovering from the virus a few months earlier,” Marla MacInnis, a spokesperson with the Department of Health and Wellness, told by email. “The individual was tested twice. The first test was indeterminate, and the second test just met the threshold for positive. We continue to work with the national lab to identify whether this was a true reinfection but are aware that we may never be able to confirm.”

The province has had no other reinfections, she said.

In some regions, the data gets murky.

Alberta Health Services confirmed to that they are “monitoring re-infections, among other ongoing surveillance.”

However, they couldn’t say whether they had detected any reinfections.

“That data is not currently available,” Tom McMillan, assistant director of communications at Alberta Health Services, said in an email. “We are exploring ways to effectively report these in the future.”

Noemie Vanheuverzwijn, a spokesperson for Quebec’s Health Department told that they do have some cases they’re investigating, saying in an emailed statement that “cases with a second episode of COVID-19 are under genomic analysis to assess whether they are reinfection cases.”

But the number of cases is unknown.

“Our system does not currently allow us to obtain the number of cases, but we are working to ensure that this data is eventually included in our database,” she wrote.


In the grand scope of things, reinfections are rare — a tracker run by BNO News has found 47 confirmed cases of reinfection reported worldwide, with thousands of suspected cases.

So why does it matter that the tracking of reinfections in Canada seems to be spotty?

Dr. Matthew Oughton, an infectious disease specialist and assistant professor at McGill University, told that a better picture of where reinfections are occurring could help us track variants as well.

“While we are trying to identify where these different variants are appearing, this is one of the indicators you could choose to more quickly identify the emergence of a possible variant,” Oughton said. “Because […] the information we have appears to be that variants are probably — and again, I say probably — more likely to cause reinfection.”

He said scientists believe that the different mutations the variants have could enable them to reinfect where the original strain wouldn’t be able to.

“We don’t know everything by a long stretch, but some of what we know is that the antigens, the parts of the virus that appear to people's immune systems, are different enough in these variants that the immunity that was generated from […] the natural infection with the sort of original or wild type SARS-CoV-2 doesn't perfectly connote the same kind of immunity to these variants because they're different enough,” Oughton said.

Research is ongoing into variants and reinfection in many regions, but not much data is available yet. It is theorized to be one of the factors behind a recent and huge spike of cases in Manaus, Brazil, despite the fact that three-fourths of the city was believed to have been previously infected, and should have had some degree of immunity. Two variants, B.1.1.7 and P.1 were detected in Manaus in January, according to a Lancet article investigating the resurgence of cases.

Oughton pointed out that the longer it has been since a person’s initial infection, the more likely it is that their immunity has waned, and that they could be reinfected.

“Not all reinfections are created equally,” he said. “So far, the reinfections that have been identified and reported in various case series seem to be generally less severe than the initial infection.”

Notable exceptions include the first confirmed case of reinfection in the U.S. last spring, where the patient was proven to have been infected with a distinctly different strain of SARS-CoV-2, and had a more severe reaction the second time.

But even if reinfection isn’t always a threat to an individual’s life, it still comes with a public health risk, because that individual could transmit the virus without knowing, while thinking they are still immune from it.

“I think this is obviously something that [is of a] fairly large importance in terms of what that could mean for [the] burden on local health care systems and what that could mean in terms of the need for speeding up our relatively slow roll out of vaccination,” Oughton said.

Some regions of Canada are keeping an eye out, and have found no confirmed cases of reinfection yet.

Saskatchewan Health Authority told in an email that they would track reinfections if any had been located, but that “there are no Saskatchewan cases that are considered re-infected.”

Public Health Ontario (PHO), an arm’s length Crown agency that provides scientific and technical support to the region’s public health units in order to inform the COVID-19 response, told that they do “monitor for incidents of COVID-19 reinfection in Ontario based on the case definition set out by the province.”

The definition for a confirmed case of re-infection in Ontario is fairly complex. According to the government and PHO, a person may be considered to be re-infected if there is “time-based or test-based clearance in between the two infections,” and genome sequencing has proven that the two separate infections of SARS-CoV-2 either “belong to different genetic clades or lineages OR ii) sufficient single nucleotide variations to correlate with the probability that the two episodes are caused by different viral lineages.”

A provincial spokesperson from Manitoba told that the province has not identified any confirmed reinfections, but does track them.

However, their definition for what would constitute a reinfection seems to differ from Ontario’s.

The spokesperson said in an email that “we would consider a case a re-infection if individuals test positive for a repeat time three months following a previous infection and have a compatible clinical history which may include a known new exposure to the virus.”

The way healthcare is delivered in Canada presents issues for obtaining consistent data across the country, Oughton said.

“We come across this all the time, that different provinces use different definitions, they have different guidelines, they collect data in different fashions, […] and trying to build a coherent picture across the country, that makes it very, very challenging,” Oughton said.

“This is yet another example where there should be a common set of definitions, which would then allow you to build a common set of tools to collect data and get a better picture as to what's happening across the country.”

The main issue with reinfection is how many questions still remain, Oughton said.

Does the severity of the initial infection have a bearing on reinfection? Are certain people more likely to get reinfected, and if so, why? Do different variants increase the chance of reinfection more than other variants? Do variants cause those who grow ill to have a shorter period of immunity after recovering?

Research is ongoing into these topics across the globe, but without more consistent data, the answers to those questions, and more, could remain out of reach.