CDC: Most Americans Have COVID-19 Antibodies

Carolyn Crist

March 30, 2022

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

About 95% of Americans ages 16 and older have coronavirus antibodies, according to CDC data from testing blood donor samples.

The percentage includes antibodies formed from both vaccinations and COVID-19 infections, with nearly 70% of people ages 16 and up having received at least one vaccine dose, the data shows.

The seroprevalence — or evidence of antibodies in the blood — differs slightly by age, at about 94% in ages 16-29, increasing to 96% in ages 65 and older.

That may be one reason why public health officials have said BA.2, the contagious Omicron subvariant, could lead to an uptick in cases in the U.S. but not a significant surge, according to CNBC.

At the same time, antibodies don't always indicate whether a surge will happen, the news outlet reported. In June 2021, before the Delta variant became dominant in the U.S., about 87% of Americans had antibodies, the CDC data shows.

The BA.2 variant has also led to surges in countries across Europe, which tend to have higher vaccination rates than the U.S. The Omicron subvariant is now the dominant COVID-19 strain in the U.S., according to new CDC data, accounting for nearly 55% of new coronavirus infections that have been sequenced.

As public health experts have tracked the effects of antibodies on coronavirus reinfection, they've noted a difference between people who have antibodies from vaccines and those who have them from being infected before. Antibodies from vaccination tend to decline about 4 to 6 months after a shot, CNBC reported.

The data about antibodies from an earlier infection is uncertain, with protection lasting from a few months to more than a year after infection. Even then, about one-third of people who contract COVID-19 may not develop antibodies at all, according to a CDC study published in September 2021.

So far, unvaccinated people appear to be more than twice as likely to have a reinfection, as compared with those who were vaccinated after having COVID-19, CNBC reported. Antibody protection likely also differs by variant, with those who recovered from an Omicron infection having better protection against the BA.2 subvariant.

In addition, scientists have noted the differences among various types of antibodies. Neutralizing antibodies bind to the virus and stop infection, but non-neutralizing antibodies function more "like a GPS," Hannah Newman, the director of infection prevention at Lenox Hill Hospital in New York City, told CNBC.

These antibodies "serve as a locator, indicating to other parts of the immune system that there is a problem," she said.

The current 7-day average of new COVID-19 cases is hovering around 30,000, according to the latest data from Johns Hopkins University. The rapid decline in COVID-19 cases from the Omicron variant surge has slowed, but numbers haven't begun to rise again. For now, public health officials are suggesting caution as they watch the data.

"Because people want to believe the pandemic is over, they let down their guard and behave less carefully," John Moore, PhD, a professor of microbiology and immunology at Cornell University, told CNBC.

Americans should work to be aware of their risk and make decisions based on their circumstances, he noted. In reality, no one can say for sure what will happen in coming weeks.

Sources

CDC: "Nationwide COVID-19 Infection- and Vaccination-Induced Antibody Seroprevalence (Blood donations)," "COVID Data Tracker: Variant Proportions," "Predictors of Nonseroconversion after SARS-CoV-2 Infection."

CNBC: "Majority of U.S. population has Covid antibodies, CDC says — here's what that means for you."

Johns Hopkins University: "COVID-19 Data in Motion: Tuesday, March 29, 2022."

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