The world may be focused on the most current variant of the SARS-CoV-2 virus, but a new study in eClinicalMedicine gives valuable insights into how older adults dealt with a previous variant, omicron. The upshot? People who had early versions of omicron were actually more at risk of contracting it again. 

Older adults — especially people in long-term care facilities — are most vulnerable to SARS-CoV-2 infections that can cause severe COVID-19. Previous research has found that infection risk with omicron (BA.1 and BA.2) was lower in this population. Other evidence has found that having the omicron variant gave people protective effects against reinfection. The new study looked at immunity and reinfection in those who contracted the omicron variant.

From July to September 2022, researchers studied omicron infection in 750 residents in long-term care communities in Canada. The people were all vaccinated four times with monovalent mRNA vaccines. During the study period, 133 of the 750 participants had a confirmed omicron infection. 

Having an early omicron infection (BA.1/BA.2) was linked to having a higher risk for subsequent omicron infection (BA.5) compared to those who never had an omicron infection, according to the study. But age, sex, frailty, time since vaccination and number of prior residence outbreaks didn’t significantly affect the risk. Researchers suspected that immunity could be a factor. 

“Our further exploration of humoral and T cell immunity after initial omicron infection suggested that while many older adults did experience an increase in antibody levels and neutralizing antibodies after one omicron infection, individuals with reinfections had weak humoral hybrid immune responses,” the researchers said.

“We found that some individuals had normal immune responses after the first infection, while others had very low levels of protective antibodies, which we believe was one contributing factor to why they got reinfected,” said Dawn Bowdish, PhD, a professor at McMaster University and the Canada Research Chair in Aging & Immunity.

Many residents of long-term care communities don’t have a period of enhanced post-infection protection. That means it’s important to protect them from subsequent infections, the authors said.