Getting COVID-19 a second time was once considered a rarity. Now, with the more transmissible BA.2 subvariant of Omicron spreading across the country, reinfections are becoming more common, according to immunology and infectious disease experts.
The exact frequency is unclear. Testing is limited across the country and detailed publicly available COVID-19 data is also limited.
“There is an ongoing test shortage and some information suggests that rapid antigen tests are not as accurate as we hoped against Omicron,” said Jennifer Gommerman, a 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 there are a lot of viruses circulating.”
PCR test positivity rates, hospitalization figures and sewage data in many provinces show increased transmission of the virus.
And data from around the world shows that the risk of reinfection is higher with Omicron, experts say.
“When we think about this idea of reinfection, we have to understand that we are still faced with a virus that has a unique ability to circumvent these early defenses against neutralizing antibodies,” said Jason Kindrachuk, virologist and assistant professor of medical microbiology and Infectious diseases. at the University of Manitoba in Winnipeg.
Still, cases of reinfection don’t usually cause disease symptoms to worsen, said Kindrachuk, who also holds the Canada Research Chair in Molecular Pathogenesis of Emerging Viruses.
There are many factors as to why a person can become reinfected with the virus, and researchers are trying to better understand reinfections and what this means during Omicron.
Reinfections rise in global data
Data released by Public Health Ontario last week shows some 11,730 Ontarians have been re-infected with COVID-19 since November 2020.
According to Ontario health officials, reinfection occurs when a person has had two laboratory-confirmed cases of SARS-CoV-2 with evidence that they were “separate infections caused by different lineages viral”.
South African scientists warned in December that reinfections among people who previously battled COVID-19 appeared to be more likely with Omicron than with earlier coronavirus mutants.
A recent increase in reinfections has been seen in some parts of the world such as the UK, which has rolled out a similar vaccine in Canada.
Before December 6, the proportion of daily cases in England considered to be reinfections had been below 2% for almost six months.
This rate is estimated to have risen to 9.9% in February, a Reuters analysis of UKHSA data was found.
In Italy, a spokesperson for the National Institute of Health said in February that reinfection cases accounted for around 3% of all infections, compared to around 1.5% before Omicron.
Why does reinfection occur?
There are many factors as to why a person is reinfected with COVID-19, including vaccination status and when a person received a vaccine or infection, said Dr. Lynora Saxinger, infectious disease specialist at the University of Alberta in Edmonton.
A study from Qatar and published in the New England Journal of Medicine last month found that curing a previous infection was about 90% effective in preventing reinfection with Alpha, Beta and Delta variants.
Protection against reinfection with the Omicron variant was less than 60% but “still considerable”, the authors said.
Another important aspect of reinfection risk is vaccine-induced immunity.
The strength of the immune response will depend in part on a person’s age and overall health. The very old, very young, and immunocompromised will have weakened responses, for example.
This is why the fourth doses are now being distributed to the most vulnerable populations across the country.
And while vaccines have repeatedly proven effective in preventing serious illness and hospitalization, Omicron is still “good enough to punch through the equivalent of two doses and in many cases two doses plus infection or three doses” , Saxinger said.
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Antibodies are known to disappear over time after a person is vaccinated or infected, said Benoit Barbeau, a professor in the department of biological sciences at the University of Quebec in Montreal who studies virology.
“So if you got infected in December or early January, you would already have less antibodies. That doesn’t mean you’ve totally lost your protection against infection, but you’ll definitely have less protection than say 10 days later. to have been infected,” he said.
The good news is that the immune response generated by the vaccination “is strong enough to keep us from getting a really bad disease and ending up in the hospital,” Gommerman said.
That’s why experts recommend people get a booster shot for that extra protection.
Regarding the BA.2 subvariant of Omicron, early research in Denmark suggests that reinfections with this strain appear to be rare.
What do we need to learn?
Barbeau said that as parts of Canada and other countries face a sixth wave, more data will emerge on who is being re-infected and why.
“There will be other variants. The risk of reinfection will always be there,” he said.
But he pointed out that population immunity, whether from vaccines or previous infection, is building up and allowing us to reduce transmission and hospitalization.
All of this is happening as research continues to improve vaccines, whether adapting to new variants or researching new methods of delivering vaccines such as through the nasal cavity, he said. declared.
“It is very important to continue to improve vaccines.”