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A new Canadian study found that COVID-19 infection provides strong protection against future re-infection with Omicron and hospitalization – especially when combined with vaccination.
The observational study of nearly 700,000 people aged 12 and over in Quebec, pre-released this week and not yet tested by partners, suggests that the presence of an earlier strain of the virus drastically reduces the risk of getting the original version of Omicron in the future.
“Even people who did not receive any vaccine had protection against Omicron infection,” said lead author Dr Gaston De Serres, an epidemiologist at the National Institute of Public Health in Quebec (INSPQ).
“However, the protection against hospitalization is much higher than your protection against re-infection – and obviously the good news is that if you add doses of vaccine, then you will increase your protection.”
The landmark study provides a first big look at how protection against vaccination, previous infection and combined hybrid immunity confronts Omicron in the real world in Canada and has major implications for our future vaccination guidelines.
“You don’t want to get COVID. I mean, it’s clear because it’s unpredictable, you could die, you could end up in the hospital, and you could get a long-term COVID, “said Dr. Eric Topol, a professor of molecular medicine at Scripps Research in La Jolla, California.
“However, if you had COVID before the Omicron wave and survived – this has provided an advantage.
Health workers are walking near the hospital line, on University Boulevard in Toronto on April 7. Protection against previous hospitalizations with Omicron was significant among the unvaccinated, but increased dramatically with additional doses of vaccine. (Evan Mitsui / CBC)
Hybrid immunity provides “remarkable” protection
The study also found that vaccines were more effective against Omicron infection among those previously infected than uninfected: an increase of up to 65 percent from 20 percent for a single dose, 68 percent over 42 percent for two and 83 percent over 73 percent for one dose. three.
But immunity to previous infections did not continue on its own – the study showed that the risk of re-infection with Omicron dropped from 66% after three to five months to just 35% between nine and 11 months.
Non-vaccinated individuals who were asymptomatic after infection also had only an eight percent reduction in future risk of infection, while symptomatic non-hospitalized patients had a 43 percent reduction and hospitalized symptomatic patients had a 68 percent reduction.
“The more severe the infection, the better protected you are – the more doses of vaccine, the more protected you are,” De Serres said. “And the order of your vaccine doses and the infection don’t seem to change the level of protection you’ve had.
Protection against previous infections against Omicron hospitalizations is also significant among the unvaccinated – 81%, but increases to 86% with one dose, 94% with two and 97% with three.
“What this study did confirmed that if you went through COVID, you experienced it, you will not only have good protection against hospitalization, but you will also benefit from at least one, if not two, vaccines,” Topol said.
“In fact, if you get three vaccines, you get remarkable levels of protection against infection and hospitalization… So that encourages people who are still there who had a previous COVID to go get vaccinated.”
The study also highlighted the limited extra booster dose protection among those previously infected with severe COVID-19 – as opposed to just two vaccines. (Daryl Dyke / Canadian Press)
Acceleration priorities may shift to Canada
But the findings also underscore the limited additional booster dose protection among those previously infected with severe COVID-19 – as opposed to just two vaccines.
“Our findings show that the incremental value of the third to second dose in someone who has previously been infected is marginal,” said Dr. Danuta Skowronski, head of epidemiology at the Center for Disease Control in British Columbia, who co-authored the study. the study.
“And if there are other groups that have not yet received even their first or second dose or are more susceptible in any other way – the doses will be better prioritized that way.”
De Serres said that while the study found that the effectiveness of two doses against hospitalization among those previously infected did not decrease significantly after 11 months, it also did not differ significantly from the effectiveness of three doses.
“If someone has been infected recently, should that person run away to get the vaccine right after three months?” Well, maybe not, “he said, adding that nearly half of Canadians who became infected with Omicron there has been considerable immunity in the last few months.
“The population that was infected during the fifth and sixth waves may already be fairly well protected for next season and may be offered an extra dose – but it may not be so urgent for them.
The study looks at the original BA.1 Omicron variant between 26 December and 22 March, not the BA.2 sub-variant, which has since become the dominant strain in Canada or other sub-lines such as BA.2.12.1, BA.4 and BA .5, which circulate in other parts of the world.
Nevertheless, the findings call into question the value of the decision of the National Immunization Advisory Committee (NACI) to we recommend a booster vaccine three months after infectionwhen protection against severe disease already remains high with two injections.
“It doesn’t mean the third dose didn’t increase it, but it’s from 94 percent to 97 percent,” Skowronski said. “The question really just arises, what are we trying to achieve with this?”
WATCH The WHO estimates that nearly 15 million people have died in the COVID-19 pandemic:
Nearly 15 million people died in the pandemic of COVID-19: WHO
The World Health Organization estimates that nearly 15 million people worldwide have died as a result of COVID-19 or the severity of the pandemic on health systems in the past two years. 2:01
No plans to change booster guidelines: NACI
In a statement to CBC News, a NACI spokesman said that despite the effects of the new study, there were no immediate plans to revise Canadian guidelines recommending a booster injection three months after COVID-19 infection.
“NACI is aware of recent Canadian and international evidence to suggest that hybrid immunity after infection and vaccination may provide protection against COVID-19,” said a spokesman when asked if the study could affect the booster guidelines.
“It is important to note, however, that the persistence and duration of protection provided by a previous infection may vary depending on factors such as the severity of the infection, age, the presence of comorbidities, and the variant causing the infection.”
NACI members also considered the “uncertainty” of whether infections with new variants would have similar hybrid immunity as previous variants, the challenge of documenting infections, and took a “precautionary approach in the face of uncertainty.”
“NACI makes decisions based on a set of evidence on a topic,” the spokesman said. “Which often extends beyond individual research.”
But real-world Canadian research not only provides insight into how the population’s immunity to vaccination and previous infection in Canada is maintained, it also underscores the importance of hybrid immunity in providing the greatest protection.
People walk in downtown Vancouver, British Columbia, on March 14. Canadian real-world data provides an unprecedented picture of how Canada’s population’s immunity to vaccination and previous infection is maintained – and has major implications for our vaccination strategy going forward. (Ben Nelms / CBC)
“We know that this hybrid immunity has an advantage, and this study really helped bring it home,” Topol said.
“There’s something different about the infection – it’s just exposing someone to the whole virus, so there’s a limit that you can’t fully simulate with spike mesenger protein vaccines.”
Dr Isaac Bogoch, an infectious disease physician at Toronto General Hospital and a member of the Ontario COVID-19 Vaccine Task Force, said the findings could also affect policy over vaccine mandates in Canada.
“If someone is interested in prescribing a third dose for some reason – you have to keep in mind that two doses plus infection, based on what we know today, are comparable,” he said. “So there are scientific and political implications for this study.”
De Serres said that although the infection provides significant protection against re-infection and severe illness, it is not necessarily a substitute for a vaccine against COVID-19.
“Are they identical? Maybe not, but I think they’re pretty comparable. I think the infection, from what we can see, provides protection for at least one dose,” he said.
“So if you’ve received two doses and you’re infected, you’re well protected, like three doses … for severe results, they’re really comparable.”
Skovronski said that while the findings underscored the protection gained from a previous infection, she wanted to make sure people did not leave, thinking that deliberate infection or so-called “SARS-CoV-2 parties” were a smart decision.
“It is not the intention of people to become infected intentionally, but rather, if they have been infected with up to two doses of vaccine, they can rest assured that they have good protection against severe results,” she said.
“And that’s good news for the general population.”
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