Previous COVID infection provides an 'edge' over Omicron — especially with vaccination
CBC
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A new Canadian study found catching COVID-19 provided strong protection against future Omicron reinfection and hospitalization — especially when combined with vaccination.
The observational study of close to 700,000 people age 12 and over in Quebec, released as a preprint this week and not yet peer reviewed, suggested that having an earlier strain of the virus dramatically reduced the risk of getting the original Omicron variant in the future.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, the protection against hospitalization is much higher than your protection against being reinfected — and obviously the good news is if you add vaccine doses, then you add to your protection."
The landmark study provides the first major glimpse at how protection from vaccination, prior infection and combined hybrid immunity is holding up against Omicron in the real world in Canada and has major implications on our vaccination guidelines in the future.
"You don't want to get COVID. I mean, that's clear because it's unpredictable, you could die, you could wind up in the hospital and you could get long COVID," said Dr. Eric Topol, a professor of molecular medicine at Scripps Research in La Jolla, Calif.
"However, if you did have COVID before the Omicron wave and you survived — it did provide an edge."
The study also found vaccines were more effective against Omicron infection among the previously infected than the non-infected: increasing to 65 per cent versus 20 per cent for one dose, 68 per cent over 42 per cent for two and 83 per cent over 73 per cent for three.
But prior infection immunity alone didn't last — with the study showing the risk of an Omicron reinfection dropped from 66 per cent after three to five months to just 35 per cent between nine and 11 months.
Unvaccinated individuals who were asymptomatic after infection also had only an eight per cent reduction in future risk of infection, while symptomatic non-hospitalized patients had a 43 per cent reduction and hospitalized symptomatic patients had a 68 per cent reduction.
"The more severe the infection, the better you're protected — the more vaccine doses, the more you're protected," De Serres said. "And the order of your vaccine doses and infection did not appear to change the degree of protection you had."
Protection from previous infections against Omicron hospitalizations was also significant among the unvaccinated at 81 per cent, but increased to 86 per cent with one dose, 94 per cent with two and 97 per cent with three.
"What this study did was reinforce that if you got through COVID, you survived it, you will not only have a good protection from hospitalizations, but also you benefit from at least one if not two shots of vaccine," said Topol.
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