With nearly 60% of the eligible U.S. population fully vaccinated, most of the nation's blood supply is now coming from donors who have been inoculated, experts said. That's led some patients who are skeptical of the shots to demand transfusions only from the unvaccinated, an option blood centers insist is neither medically sound nor operationally feasible.

Emily Osment, an American Red Cross spokesperson, said her organization has fielded questions from clients worried that vaccinated blood would be "tainted," capable of transmitting components from the COVID-19 vaccines. Red Cross officials said they've had to reassure clients that a COVID-19 vaccine, which is injected into muscle or the layer of skin below, doesn't circulate in the blood.

"While the antibodies that are produced by the stimulated immune system in response to vaccination are found throughout the bloodstream, the actual vaccine components are not," Jessa Merrill, the Red Cross director of biomedical communications, said in an email.