A new study has found that previous infection with one type of Omicron variant of the coronavirus did not protect elderly individuals in long-term care facilities and retirement homes from reinfection within a few months.

The lead author and immunologist at McMaster University, Dawn Bowdish, says the study's results are surprising as they challenge current thinking about hybrid immunity.

It is expected that people will gain hybrid immunity against the coronavirus when they are vaccinated against the virus and also infected, but in the McMaster study, vaccinated elderly individuals who contracted Omicron variants in early 2022 were about 20 times more likely to get reinfected with another Omicron variant later that year, compared to vaccinated elderly individuals who did not experience infection.

Bowdish explained that the study suggests people should stay updated on their COVID vaccines and not assume that previous infection protects them, but she also says it's unknown whether the study's findings apply to the general population or are specific to the elderly.

The study tracked 750 vaccinated elderly individuals in long-term care facilities and retirement homes across Ontario, and it was published today (Monday) in eClinicalMedicine, one of The Lancet's medical journals.

Bowdish, who is a researcher with Canada's Research in Aging and Immunity at McMaster University, noted that the study shows there is still much unknown about how people contract the coronavirus, emphasizing that the Canadian vaccination strategy is based on the assumption that recent infection will protect you from reinfection for at least a short period of time, but the study shows that for some variants, this is not true for some individuals.