Definition

A vaccine composed of the bacteriophage phi X 174, a virus that infects the bacterium Escherichia coli (E. coli), that can be used as a diagnostic agent to measure immune function of immunocompromised patients. Upon administration of the bacteriophage phi X 174 vaccine, the bacteriophage may activate the immune system to induce bacteriophage phi X174 specific antibody responses. The clearance of phage from the blood and the measurement of phage neutralization by antibodies can be used to assess the immune status of patients with suspected antibody-mediated immunodeficiency and to measure the response to certain therapies.