By the fall of 2022, most people (96%) in the United States had COVID-19 antibodies from a previous infection or vaccination, a federal study of blood donor data has found. But for older adults, measures of protective immunity were lower, underscoring this age group’s continued vulnerability to infection, researchers say.
Investigators used data from a nationwide cohort of blood donors aged 16 years and older. The overall prevalence of antibodies in this group rose from 68% in the second quarter of 2021 to 96% in the third quarter of 2022, they found. This increase likely contributed to the reduced rates of severe disease and death from COVID-19 in 2022 and 2023 compared with early pandemic outcomes, investigators said.
Hybrid immunity, from a combination of vaccination and prior infection, has been found to provide better protection than from infection or vaccination alone. Overall, 48% of blood donors had hybrid immunity during the third quarter 2022, the data showed. But signs of hybrid immunity were 37%, among adults aged 65 years and older.
Three factors may have contributed to the latter finding, including higher vaccination coverage and the earlier availability of COVID-19 vaccines for this age group, as well as seniors’ overall greater use of behavioral measures to avoid infection, the researchers theorized.
Lower levels of infection-induced and hybrid immunity could further increase the risk for severe disease in this group, wrote Jefferson M. Jones, MD, of the National Center for Immunization and Respiratory Diseases, at the Centers for Disease Control and Prevention. Older adults are already at the highest risk for severe COVID-19 outcomes, he and his colleagues noted.
The findings highlight “the importance for adults aged 65 years and older to stay up to date with COVID-19 vaccination and have easy access to antiviral medications,” the authors concluded.
The study was published in the CDC’s Morbidity and Mortality Weekly Report (MMWR).
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