More than 20% of blood donations to the American Red Cross from unvaccinated people in the first week of March had COVID-19 antibodies, according to data obtained by CNN.
Meaning, about one-in-five donors could have been exposed to the coronavirus or had it recently, whether or not they had symptoms. A positive antibody test does not necessarily confirm infection or immunity, the Red Cross notes.
The data from the Red Cross mirrors findings from a Pew Research Center survey last month. They found 25% of Americans said they have had COVID-19, or about one-in-four people. In a survey in September, that number was closer to one-in-seven Americans who said they had contracted COVID-19.
The prevalence of COVID-19 antibodies in blood donations has been increasing, according to the data. Only about 1.5% of blood donations in July had antibodies, which increased to 4% in October and 12% in January. In the first week of March, it was 21%.
Between July and March so far, the Red Cross has tested more than 3.3 million blood donations from unvaccinated people in 44 states for COVID-19 antibodies.
A vaccine expert told CNN while the 21% seems high, he was impressed by the roughly 80% of donations without antibodies, people who had not been exposed to COVID-19.
"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,” Dr. William Schaffner, a longtime adviser to the US Centers for Disease Control and Prevention on vaccines told CNN.
Herd immunity is achieved when enough people in a population are protected from a disease by antibodies to the virus. Health experts have not agreed on a percentage of the population needed to reach herd immunity against COVID-19, but some estimate it to be around 80%.