A new study has found that previous infection with an Omicron variant of COVID-19 does not protect seniors in long-term care and retirement homes from being infected again within a few months.
McMaster University senior author and immunologist Dawn Bowdish says the study results are surprising because they challenge current thinking about hybrid immunity.
People are expected to gain hybrid immunity to COVID-19 when they are both vaccinated against the virus and infected.
But in the McMaster study, vaccinated seniors who became infected with Omicron variants in early 2022 were about 20 times more likely to become infected again later that year with a different Omicron variant.
That compares to seniors who were vaccinated but not infected.
Risk of contracting COVID-19 again even if you are fully vaccinated
According to Bowdish, the study suggests that people should stay up to date with their COVID-19 vaccinations and not assume that a previous infection will protect them.
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But Bowdish also says it's not known if the study results apply to the general population or if they apply specifically to seniors.
The study followed 750 vaccinated seniors in long-term care and retirement homes across Ontario.
It was published in eClinicalMedicine, one of The Lancet's medical journals, on Monday.
The study shows there's still a lot of unknowns about how the virus that causes COVID-19 infects people, Bowdish said.
“(Canada's) vaccination strategy is based on the assumption that a recent infection will protect you from infection, at least for a short period of time.” And our study shows that with some variants in some people, that just isn't the case,” said Bowdish, owner the Canada Research Chair in Aging and Immunity at McMaster University.
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