A bout of COVID-19 infection may not be sufficient for lasting immunity as the virus continues to mutate and new variants emerge.
Immunity acquired through infection by catching COVID-19 may act as a protective layer for a time, but that protection wanes as does vaccine-induced immunity, experts say, noting that infection of one variant may provide no protection against another.
Omicron’s BQ.1.1 COVID-19 subvariant. Why Experts Watch It
Omicron’s BQ.1.1 COVID-19 subvariant. Why Experts Watch It
In Canada and around the world, the BA.5 subvariant of Omicron is dominant, but the World Health Organization (WHO) tracks hundreds of others.
Since its emergence in late 2019, COVID-19 has produced multiple mutations with Alpha, Beta, Gamma, Delta and Omicron so far characterized as variants of concern.
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COVID-19 infection doesn’t always lead to a good immune response, experts say – and reinfections can occur.
So how long are you immune to COVID-19 after infection?
“In general, a period of about six months [after getting COVID-19] probably leaves you pretty much invulnerable to infection, as long as the virus doesn’t change between the two, or you don’t get infected with a different variant,” said Johns Hopkins Center principal investigator Dr. Amesh Adalja. for Health Security. at the Bloomberg School of Public Health.
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Just as with vaccine-induced immunity, by month six there is “literally no protection” against the immunity acquired through infection, said Dr. Catherine Hankins, a professor at the School of Health. Population and Global Health from McGill University, and co-chair of the Canadian COVID-19 Immunity Task Force.
The type of variant with which one is infected also plays a role in so-called natural immunity.
For example, if you were infected with the Delta variant and then exposed to Omicron, you wouldn’t be protected against Omicron, although protection against severe disease is likely still intact, Adalja said.
That said, there will be a certain level of protection, lasting two months, where you are not at risk of being infected with another sub-variant of Omicron if you were initially infected with another sub-line. of Omicron, Adalja said.
“It all depends on how far this variant is from the version of the virus you were infected with.”
What does science show?
There is no guarantee that infection will induce immunity, according to a review by the COVID-19 Immunity Task Force.
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A Canadian study published in the Pediatric Infectious Disease Journal in May found that one in eight people who contract COVID-19 do not develop antibodies in their blood due to the disease. And children are half as likely to develop immunity to infection, according to CITF-funded research.
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Meanwhile, more and more data suggests that being infected with Omicron does not prevent you from catching the virus again.
A pre-printed US study – which has not been peer reviewed – published in January 2022 suggested that mild Omicron infection does not confer sufficient immunity to prevent future infections, while Delta variant infections, which tended to be more severe, produced higher protection.
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According to the US Centers for Disease Prevention and Control (CDC), COVID-19 antibodies peak within the first few weeks after symptoms appear, then fall below detectable limits two to three months after infection.
Another US study published in the New England Journal of Medicine in July showed that the BA.4 and BA.5 subvariants of Omicron substantially evade neutralizing antibodies induced by both vaccination and infection.
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A paper from Qatar, the results of which were posted online last week in a pre-peer review letter, found that protection against prior infection against BA.4 or BA.5 reinfection was modest when the The previous infection was caused by a pre-Omicron variant but strong when caused by a post-Omicron sub-variant (including BA.1 or BA.2).
More research is needed, Adalja said.
“It’s not one size fits all. It’s hard to predict because we don’t have a lot of data on these variants and who is infected with it versus who has been infected in the past.
Despite the antibodies one can develop from COVID-19 infection, vaccination remains an important tool at our disposal – whether you are infected or not, experts say.
“The best form of protection, actually, is to get all your vaccine doses,” Hankins said, adding that infection comes with the risk of long COVID and other complications.
“It’s just too much of a risk to take for something that’s vaccine preventable,” she added.
Compared to natural immunity from an episode of COVID-19, vaccine-induced immunity might be more protective with respect to certain variants, Adalja said.
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This is where hybrid immunity comes in. According to the WHO definition, this is immune protection in people who have had COVID-19 at least once and who have received one or more doses of the vaccine.
The Qatari study showed that hybrid immunity with two or three doses of an mRNA vaccine and prior infection was associated with the highest degree of protection against symptomatic infection.
“Hybrid immunity appears to be most potent in protecting against severe disease, hospitalization, and death,” Adalja said.
“It adds and increases the natural immunity you get from infection.”
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