An elderly woman wearing a medical mask looks into the camera. Two other elderly people in medical masks stand behind her.

Hybrid Immunity’s Not a ‘Panacea’ in the Age of Omicron

The story goes that once you've been infected with Omicron, you've got natural immunity to COVID-19. But that's not the story for everyone.


It’s widely believed that developing a natural immunity to COVID-19 through infection can lessen your chances of reinfection, but it turns out that this may not be the whole story for older adults.

Focusing on residents of long-term care homes in particular, a new study has found that early infections of the SARS-CoV-2 Omicron variant amongst older adults were actually associated with higher chances of becoming reinfected in the future. The study was led by researchers at McMaster University and published in The Lancet.

Older adults face increased risks of contracting COVID-19, and tend to deal with more severe physical and mental health outcomes from the disease. What’s more, older adults living in congregate settings such as long-term care facilities or retirement homes often have to content with frequent outbreaks of the disease.

While vaccination against COVID-19 is now widespread throughout Canada, the team behind the study was interested in learning how hybrid immunity — that is, both vaccination and a previous infection — can affect older adults’ chances of becoming reinfected with the Omicron variant. To do this, they tracked 750 vaccinated residents of long-term care and retirement homes in Ontario over a 75-day period. The data came from the COVID in Long-Term Care Study.

The median age of the residents included in the study was 87 years, and all had received four COVID-19 vaccinations. A total of 36% had had at least one prior COVID-19 infection, while 17% had at least one Omicron infection specifically.

Of the 750 residents observed in the study, 133 were infected with the Omicron variant during the 75-day study period. Surprisingly, the majority of these were actually patients who had already been infected with the Omicron variant prior to the study.

Upon looking at these residents more closely, the team found that they tended to have lower levels of certain antibodies that can help fight off COVID-19 infections. These results demonstrate that we can’t necessarily assume natural immunity against COVID-19 is effective amongst all populations, especially as new variants continue to emerge.

“Overall, our observations caution that […] hybrid immunity [is] not the same in all older adults, and hybrid immunity should not be considered a panacea against future SARS-CoV-2 infection, whether from cross-subvariant Omicron infections, or future variants of concern,” the authors conclude.

To help keep everyone safe, we should continue to follow public health guidelines and get vaccinated as recommended by public health experts.

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Emily Deibert is a PhD student in the Department of Astronomy & Astrophysics at the University of Toronto with a passion for science outreach and communication. She earned her HBSc (Astronomy, English, and Mathematics) at the University of Toronto. She is excited about turning scientific research into stories and sharing these stories with the public.