Prior Omicron infection didn’t protect some seniors from reinfection, McMaster study finds


Published August 21, 2023 at 3:39 pm

A new study has found that previous infection with an Omicron variant of COVID-19 did not protect seniors in long-term care and retirement homes from getting reinfected within a few months.

Senior author and McMaster University immunologist Dawn Bowdish says the study results are surprising because they challenge the current thinking about hybrid immunity.

People are expected to gain hybrid immunity to COVID-19 when they’ve been both vaccinated against the virus and have also been infected.

But in the McMaster study, vaccinated seniors who had been infected with Omicron variants in early 2022 were about 20 times more likely to be reinfected with another Omicron variant later that year.

That’s compared to seniors who were vaccinated but had not been infected.

Bowdish says the study suggests people should stay up-to-date with their  COVID-19 vaccinations and not assume a previous infection is protecting them.

But Bowdish also says it’s not known whether or not the study results apply to the general population or if they are specific to seniors.

The study followed 750 vaccinated seniors in long-term care and retirement homes across Ontario.

It was published Monday in eClinicalMedicine, one of The Lancet’s medical journals.

The study shows that a lot is still unknown about how the virus that causes COVID-19 infects people, said Bowdish.

“(Canada’s) vaccination strategy is predicated on this assumption that having had a recent infection will protect you from an infection at least for a short period of time. And our study shows that for some variants that’s just not true in some people,” said Bowdish, who holds the Canada Research Chair in Aging and Immunity at McMaster University.

Canadian Press health coverage receives support through a partnership with the Canadian Medical Association. CP is solely responsible for this content.

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