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More than three years into the pandemic, an overwhelming majority of Americans have some level of COVID-19 antibodies circulating in their bodies, the U.S. Centers for Disease Control and Prevention (CDC) found in a new report.
With the help of blood-donation centers, CDC scientists analyzed data from blood samples of about 143,000 Americans ages 16 and older from July through September 2022 and found that 96% of them contained antibodies to SARS-CoV-2. Previous data similarly collected between April and June 2021 showed that only 68% of blood samples contained COVID-19 antibodies.
The CDC also found that the percentage of people with hybrid immunity—meaning they’ve gained protective antibodies from both vaccination and infection—has increased over time. Of everyone included in the latest data, 48% possessed hybrid immunity. Hybrid immunity is more protective against infection and severe illness than immunity received exclusively from either infection or vaccination, in part because it generates wider-ranging defenses against the virus, and constantly changing variants have made it difficult to predict exactly how long immunity from either infection or vaccination will last.
Though hybrid immunity is stronger than immunity from vaccination alone, that’s not a reason to go looking for COVID-19, the scientists say. The risks of infection—such as Long COVID—still outweigh the immunity benefits.
Some of the study’s most encouraging immunity data about vaccination came from seniors. Across all age groups, those 65 and older were the least likely to carry any antibodies acquired from actual illness; just 37% had hybrid immunity, compared to 60% in the youngest age bracket (ages 16-29). That so many older adults had COVID-19 antibodies despite their lower infection rates “reflects the success of public-health infection prevention efforts,” the authors write. The new data on immunity also provide some evidence to assuage concerns that the vaccines may not be as effective against Omicron subvariants, since people who were vaccinated had lower rates of infection than those who weren’t vaccinated.
Although the study didn’t include data on how many vaccines and boosters participants had received—just whether or not a person was vaccinated—the data are a reminder to stay up-to-date on the CDC’s recommended vaccine and booster schedule (especially for older adults, who are at the highest risk for severe illness, hospitalization, and death from COVID-19).
The CDC recommends that adults age 65 and older who are at least four months out from their last shot—and younger people who are immunocompromised—get a second bivalent mRNA booster. An annual booster schedule for all other Americans is expected to be rolled out in the fall.