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A new Canadian study finds that infection with the COVID-19 virus offers powerful protection against future Omicron infection and hospitalization – especially when combined with vaccination.
Observational Study Of the nearly 700,000 people aged 12 or older in Quebec released as an initial draft this week and not yet reviewed, they suggested that having a previous strain of the virus significantly reduces the risk of acquiring the original variant of Omicron in the future.
“Even in people who did not receive any vaccine there was protection against omicron infection,” said lead author Dr. Gaston de Serres, an epidemiologist at the Quebec National Institute of Public Health (INSPQ).
“However, protection against hospitalization is much higher than protection against re-infection – and obviously the good news is that if you add doses of the vaccine, you add to your protection.”
The landmark study provides the first major glimpse into how vaccination protection, past infection, and hybrid co-immunity against Omicron is prevented in the real world in Canada and has major implications for our future vaccination guidelines.
Eric Topol, professor of molecular medicine at Scripps Research in La Jolla, California.
“However, if you had COVID before the Omicron wave and survived – it gave you an advantage.”
Hybrid immunity provides ‘remarkable’ protection
The study also found that vaccines were more effective against omicron infection among previously infected than uninfected: it increased to 65 percent versus 20 percent for a single dose, 68 percent over 42 percent for two and 83 percent over 73 percent for three cents.
But immunity to previous infections alone was not short-lived — the study showed that the risk of re-infection with omicron dropped from 66 percent after three to five months to just 35 percent between nine and 11 months.
Unvaccinated individuals who did not develop symptoms after infection also had only an 8 percent reduction in future risk, while patients who did not receive hospital treatment decreased by 43 percent, and asymptomatic patients decreased in hospital by 68 percent.
“The more severe the infection, the better your protection — the higher the doses of the vaccine, the more protected you are,” de Serres said. “The order of vaccine doses and infection do not seem to change the degree of protection they have.”
Protection from previous infections against Omicron treatment was also significant among the unvaccinated at 81 percent, but increased to 86 percent with one dose, 94 percent with two doses and 97 percent with three.
“What this study did was reinforce that if you had COVID, you survived it, you would not only have good protection from hospitalization, but also benefit from at least one injection if not two vaccines,” Topol said.
“In fact, if you get three shots, it will reach remarkable levels of protection against infection and hospitalization … so it encourages people who are still abroad who have previously had Covid to get vaccinated.”
Supporter priorities in Canada can change
But the findings also highlight the limited additional protection of a booster dose among those previously infected against severe COVID-19 — as opposed to just two injections.
“Our results suggest that the increased value of the third dose over the second in a previously infected person is marginal,” said Dr. Danuta Skoronsky, chief of epidemiology at the British Columbia Center for Disease Control who co-authored the study.
“And if there are other groups left who have not yet received their first or second dose or are at higher risk – the doses would be better arranged that way.”
De Serres said that while the study found that the effectiveness of the two doses against hospitalization among previously infected patients did not diminish significantly after 11 months, it also did not differ significantly from the effectiveness of the three doses.
“If someone has been infected recently, should that person run to get the vaccine after three months? Well, maybe not,” he said, adding that nearly half of Canadians who infected with omicron Over the past few months great immunity.
“People who have been injured during the fifth and sixth waves may already be well protected for next season and maybe they can be given an extra dose – but that probably won’t be a stress for them.”
The study looked at the original BA.1 Omicron variant between December 26 and March 22, not the BA.2 variant that has since become the dominant strain in Canada or other subspecies such as BA.2.12.1, BA.4 and BA.5 that are traded in other parts of the world.
However, the findings call into question the value of the NACI decision. I recommend a booster dose three months after the injurywhen protection against severe disease remains already high at two doses.
“It’s not that the third dose didn’t increase it, but it’s from 94 percent to 97 percent,” Skoronsky said. “It really begs the question, what are we trying to achieve with this?”
Watch | The World Health Organization estimates that nearly 15 million people have died in the COVID-19 pandemic:
No plans to change reinforcement guidelines: NACI
In a statement to CBC News, a NACI spokesperson said that despite the implications of the new study, there are no immediate plans to reconsider Canadian guidelines recommending a booster dose three months after infection with COVID-19.
Asked if the study could affect booster guidance, the spokesperson said, “NACI is aware of recent Canadian and international evidence suggesting that hybrid immunity after infection and vaccination can provide protection against COVID-19 disease.”
“However, it is important to note that the durability and duration of protection conferred by prior infection may vary due to factors such as severity of infection, age, presence of comorbidities and the infective variable.”
NACI members also considered “uncertainty” about whether infection with new variants would have similar hybrid immunity as with previous variants, the challenge of documenting infection and took a “precautionary approach in the face of uncertainty.”
“NACI makes decisions based on the body of evidence relating to a topic,” the spokesperson said. “which often bypasses individual studies.”
But Canadian research in the real world not only provides insight into how a population’s level of immunity lags behind vaccination and previous infection in Canada – it also highlights the importance of hybrid immunity for the greatest protection.
“We know this hybrid immunity has an advantage and this study really helped restore that immunity,” Topol said.
“There’s something different about infection – it exposes the entire virus to a person, so there is some advantage that you can’t fully simulate with Spike Messenger protein vaccines.”
Dr. Isaac Bogosh, an infectious disease physician at Toronto General Hospital and a member of the Ontario COVID-19 Vaccine Task Force, said the findings could also influence policies around vaccine mandates in Canada.
“If someone is interested in getting a third dose for any reason – you should consider that the two doses plus infection, based on what we know today, are comparable,” he said. “So there are scientific and policy implications for this study.”
De Serres said that while the infection offers great protection against reinfection and severe illness, it is not necessarily a substitute for the COVID-19 vaccine.
He said, “Are they identical?
“So if you take two doses and get infected, you’re well protected, similar to three doses… for serious, really comparable results.”
Skoronsky said that while the results confirm the protection obtained from a previous infection, she wants to make sure that people don’t come thinking that intentional infection or the so-called “SARS-CoV-2 limbs” are a smart decision.
“It’s not meant for people to intentionally become infected, but if they do get infected with up to two doses of the vaccine, they can be reassured that they are well protected against dangerous outcomes,” she said.
“And this is good news for the population in general.”