This weekend, a hospital in Houston became the first in the United States to treat a seriously ill Covid-19 patient with blood plasma collected from a recovered patient. Plasma therapy, which delivers antibody-packed plasma from recovered patients to those still fighting off infection (or preemptively to those at high risk of infection), is not a new or particularly complex procedure. But it could be a critical weapon in the fight against SARS-CoV-2—and it’s already coming online.