It is paradoxical that zinc-precipitated gamma globulin administered in small doses apparently could protect the recipient against epidemic hepatitis while the same material may produce serum hepatitis. Cold-ethanolfractionated gamma globulin does not produce serum hepatitis but protects almost all exposed susceptible persons against the more severe symptoms of epidemic hepatitis. The most likely explanation is that in the carrier state hepatitis viruses of more than one antigenic strain are present in the blood stream and that the recipient of the carrier's blood can be protected by gamma globulin in accordance with how closely the transfused virus strain is antigenically related to the strain or strains responsible for epidemic hepatitis. The so-called passive-active immunization afforded by gamma globulin in epidemic hepatitis seems promising, and a method of testing it in closed institutions is proposed.
Stokes J. IMMUNIZATION IN VIRAL HEPATITIS. JAMA. 1960;172(7):652-655. doi:10.1001/jama.1960.03020070010003