Pre-exposure Prophylaxis of Viral Hepatitis with Immune Serum Globulin in an Endemic Area: A Trial in Field Units of the Israel Defence Forces

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Abstract
Field units in the Israel Defense Forces represent a high risk group for type A infectious hepatitis. Very large scale post-exposure prophylaxis with immune serum globulin (ISG) has been successfully employed for the past decade with a reduction in incidence and an elimination of overt epidemic cycles. The use of pre-exposure prophylaxis in an indigenous population in whom .apprx. 70% have antibody to hepatitis A virus at age 18 was compared in a field trial with the routine post-exposure method. Units were randomized into an intervention group (A) in which all subjects were to receive ISG (70% were in fact immunized), a 2nd group (B) in which 50% of subjects were to be immunized (36% were actually immunized) and a non-immunized control group (C). During the trial, incidence rates in the non-immunized study population dropped well below predicted levels. The incidence rates were zero in group A, 1.31/1000 in group B (0.61/1000 among the immunized and 1.72/1000 among the non-immunized) and 2.49/1000 on group C over the 6 mo. follow-up. Pre-exposure ISG afforded excellent protection and, even at the low rate of incidence, was cost-effective. The possibility of herd immunity is discussed.