(HealthDay News) — Infection with an omicron variant of SARS-CoV-2 is associated with an increased risk of reinfection among residents of long-term care and retirement homes, according to a study published in eClinicalMedicine.

Researchers examined the incidence of infection with omicron variants in 750 residents of long-term care and retirement homes from July to September 2022. All of the residents had received 4 doses of a monovalent mRNA COVID-19 vaccine.

The researchers found that, before the observation period, 35.7% of participants had at least 1 SARS-CoV-2 infection, and 17.5% had 1 omicron infection.

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During the observation period, 17.7% of participants had an omicron infection. Among these participants, 57.1% had a prior omicron infection. Among participants without an omicron infection during observation, 71.0% had no prior SARS-CoV-2 infections.

The researchers noted that the cumulative probability of an omicron infection was highest in participants with 1 prior omicron infection and no pre-omicron SARS-CoV-2 infections before observation (P <.0001).

The researchers measured immunological parameters in a subset of 318 participants. These analyses revealed that, after their initial omicron infection, reinfected participants had lower serum neutralizing antibodies to ancestral and omicron BA.1 SARS-CoV-2 as well as lower anti-receptor binding domain immunoglobulin G and immunoglobulin A antibodies.

“Overall, our observations caution that immunological features of hybrid immunity are 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 researchers wrote.

Two researchers disclosed ties to the pharmaceutical industry.

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