Data indicate 96% of people in US have SARS-CoV-2 antibodies
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Key takeaways:
- Nearly all blood donors in a new analysis had antibodies against SARS-CoV-2.
- Almost half had hybrid immunity from vaccination and infection.
Among more than 72,000 blood donors in the United States aged 16 years or older, 96% had antibodies against the virus that causes COVID-19 by late last year, according to a new analysis.
Jefferson M. Jones, MD, MPH, a medical officer in the CDC’s National Center for Immunization and Respiratory Diseases, and colleagues found that infection-induced and hybrid immunity increased over the study period, from mid-2021 to the third quarter of 2022, which they said may be contributing to lower rates of severe disease and death compared with earlier phases of the COVID-19 pandemic.
Among those carrying antibodies against SARS-CoV-2, nearly half gained the antibodies through hybrid immunity, a mix of protection from vaccination and infection.
“Changes in testing behaviors and reporting requirements have hampered the ability to estimate the United States’ SARS-CoV-2 incidence,” Jones and colleagues wrote.
“Hybrid immunity ... has been reported to provide better protection than that from infection or vaccination alone,” they wrote, adding that the goal of the new analysis was to “estimate the incidence of infection and the prevalence of infection- or vaccination-induced antibodies (or both).”
In July 2020, the CDC, Vitalant, the American Red Cross, Creative Testing Solutions and Westat established a nationwide cohort of 142,758 people who had donated blood at least two times in the previous year, according to Jones and colleagues.
Donations collected between April 2021 and June 2021 were tested for SARS-CoV-2 antibodies, and up to one donation per donor was randomly tested each quarter starting in 2022. At each donation, donors were asked if they had been vaccinated against COVID-19.
The new analysis estimated vaccine-induced, infection-induced and hybrid immunity for four 3-month periods — April 2021 through June 2021, January 2022 through March 2022, April 2022 through June 2022 and July 2022 through September 2022.
Jones and colleagues analyzed data on 72,748 participants with available immune and vaccination status at time of donation.
During the second quarter of 2021, 68.4% of participants had SARS-CoV-2 antibodies resulting from vaccination, infection or both. From January 2022 through March 2022, the rate of donors with antibodies increased to 93.5%, and it rose further to 96.4% in the third quarter that year.
Among the 96.4% of donors who had SARS-CoV-2 antibodies, 22.6% had antibodies through infection alone, 26.1% had antibodies through vaccination alone and 47.7% had antibodies through hybrid immunity. Hybrid immunity was found to be lowest among donors aged 65 years or older.
“Both infection-induced and hybrid immunity increased during the study period,” Jones and colleagues concluded. “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,” they wrote.
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