Their bodies produce antibodies in response to these vaccines, and the hope is these antibodies can be used to treat people with the diseases.

The approach is similar to the idea behind transfusing plasma from Ebola survivors into patients. No one knows if it is actually helping, but experiments are under way in Liberia and at Emory University Hospital in Atlanta to see if the blood of survivors might kick-start the immune response in a patient.

When a person or animal is infected, the body produces antibodies and immune cells to fight the invading germs. The human immune system is especially advanced and can produce both antibodies and immune cells called T-cells that “remember” a previous infection and can often prevent a second infection by the same germ.