Convalescent Serum

Serum (Blood Draw) taken from a patient that has completely recovered from an infectious disease is called Convalescent Serum.  In which the bodies own immune system created Antibodies against the disease.

The Antibodies are detectable in a lab, even though the patient has completely recovered and shows no symptoms.  Various tests such as IgG and IgM are used.

Also see:  Acute-Phase Serum (active viral/bacterial serum)