Almost all blood donors had severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies from previous infection or vaccination by the third quarter of 2022, with the prevalence of hybrid immunity lowest for adults aged ≥65 years, according to research published in the June 2 issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.

Jefferson M. Jones, M.D., from the CDC in Atlanta, and colleagues estimated the incidence of infection and prevalence of infection- or vaccination-induced SARS-CoV-2 antibodies using data from a nationwide, longitudinal cohort of blood donors.

The researchers found that an estimated 68.4 percent of persons aged ≥16 years had infection- or vaccination-induced SARS-CoV-2 antibodies during the second quarter of 2021, including 47.5, 12.0, and 8.9 percent from vaccination alone, infection alone, and both, respectively. Overall, 96.4 percent had SARS-CoV-2 antibodies by the third quarter of 2022, including 22.6, 26.1, and 47.7 percent from infection alone, vaccination alone, and hybrid immunity, respectively.

Adults aged ≥65 years had the lowest prevalence of hybrid immunity (36.9 percent), and they had the highest risk for severe disease if infected; the prevalence of hybrid immunity was highest among those aged 16 to 29 years (59.6 percent).

“Compared with vaccine effectiveness against any infection and against severe disease or hospitalization, the effectiveness of hybrid immunity against these outcomes has been shown to be higher and wane more slowly,” the authors write.

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