Serological hepatitis A virus infections and ratio of clinical to serological infections in a controlled trial of pre-exposure prophylaxis with immune serum globulin.

Seroconversion to hepatitis A virus was studied in a sub sample of 802 Israeli military recruits (611 men and 191 women) who were taking part in a randomised controlled trial of pre-exposure immune serum globulin (ISG) for the prevention of viral hepatitis. On intake into the service 35% of the men and 47% of the women were negative to hepatitis. A virus antibody (anti-HAV). After three years 7 of 71 men (9.9%) who had not received pre-exposure ISG had become positive to anti-HAV compared to 2 of 83 (2.4%) who had received it; the statistical significance of this difference was p = 0.052. At two years 2 of 30 women (6.7%) who had not received ISG had converted compared to 1 of 43 (2.3%) who had received ISG (p = 0.37). Pooling the sexes gave conversion rates of 8.9% in those not immunised and 2.4% in those immunised (p = 0.029). The sex adjusted odds ratio was 4.0 (95% confidence limits 1.3-19.0). The morbidity rates for clinical non B hepatitis over the three year period among 12 835 men were 7.2 per 1000 in those not immunised and 3.6 per 1000 in those immunised (p = 0.004). Point estimates of the ratio of clinical hepatitis to seroconversion in men ranged from 0.25 to 0.30. It is concluded that pre-exposure administration of ISG effectively prevented clinical expression of viral hepatitis, apparently reduced seroconversion, and did not induce passive-active immunisation.