What we know so far about getting COVID-19 twice in the age of Omicron

Getting COVID-19 a second time was once considered a rarity. Now, with the more transmissible Omicron subvariant BA.2 spreading throughout the country, reinfections are becoming more common, immunology and infectious diseases experts say.

Exactly how common is not clear. Testing is limited across the country and detailed COVID-19 data that's publicly available is also limited. 

"There is a dearth of testing that's happening and there's some information coming out to suggest that the rapid antigen tests are not as accurate as we hoped against Omicron," said Jennifer Gommerman, professor of immunology at the University of Toronto, and the Canada Research Chair in tissue specific immunity. 

"Prevalence is a difficult question to answer, but we know that there's lots of virus going around."

PCR test-positivity rates, hospitalization figures, and wastewater data in many provinces are showing increased transmission of the virus. 

And data from around the world do show reinfection risk is higher with Omicron, experts say.

"When we think about this idea of reinfection, we have to appreciate we are still facing a virus that has a unique ability to circumvent those early defences from neutralizing antibodies," said Jason Kindrachuk, a virologist and assistant professor in medical microbiology and infectious diseases at the University of Manitoba in Winnipeg.

Yet, reinfection cases largely do not cause worse symptoms of the disease, said Kindrachuk, who is also the Canada Research Chair in the molecular pathogenesis of emerging viruses.

There are many factors as to why someone may be reinfected with the virus, and researchers are trying to get a better understanding of reinfections and what it means during Omicron.

Data released by Public Health Ontario last week shows some 11,730 Ontarians have been reinfected with COVID-19 since November 2020. 

Reinfection, according to Ontario health officials, is when someone has had two lab-confirmed cases of SARS-CoV-2 with evidence that these were "separate infections caused by different viral lineages."

South African scientists had warned in December that reinfections among people who've already battled COVID-19 appeared to be more likely with Omicron than with earlier coronavirus mutants.

A recent rise in reinfections has been seen in parts of the world like the United Kingdom, which had a similar vaccine rollout to Canada.

Before Dec. 6, the proportion of daily cases in England thought to be reinfections had been below two per cent for nearly six months.