More than 20% of blood donations from unvaccinated people made during the first week of March had COVID-19 antibodies, according to data shared by the American Red Cross to CNN.
The American Red Cross tested more than 3.3 million donations from unvaccinated people for the presence of COVID-19 antibodies from mid-June 2020 to early March 2021, which included participants in 44 states.
The results showed about 7.5% of the donations tested during that span included COVID-19 antibodies, which means the donors were likely infected with the coronavirus prior to the donation.
The American Red Cross did, however, reiterate that "a positive antibody test result does not confirm infection or immunity," but acknowledged that it could indicate the person was exposed to COVID-19, "regardless of whether an individual developed the symptoms."
The organization reports it saw an increase in antibody prevalence among unvaccinated blood donors over time consistent with more cases being reported nationwide.
According to data shared with CNN via email, the American Red Cross reports about 1.5% of donations tested during the first week of July showed COVID-19 antibodies were present, which increased by nearly 4% during the first week of October, about 12% during the first week of January and nearly 21% during the first week of March.
"Blood donors are not a random sample of the general population, but they're interesting," said Dr. William Schaffner, an adviser to the US Centers for Disease Control and Prevention on vaccines, via CNN.
Dr. Schaffner added that two things stood out in the data.
"The first is that a substantial portion of the US population has experienced Covid, at least the blood donor population, knowingly or unknowingly. The other is that a huge proportion of the US population has not -- it's the 80%," he said. "So we can't rely just on the strategy of letting herd immunity occur naturally. We've got to vaccinate in order to get up to 80% of the population to be immune."
Throughout the pandemic, doctors and experts have strived for herd immunity, which is the point at which enough individuals are protected against the virus that it cannot spread through the population. That goal can be achieved when enough people have antibodies to the virus, so the data is reassuring.
Individuals who have recovered from the coronavirus have some protection from the virus, although scientists are still uncertain how long it lasts or whether it will protect against new variants.
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