TIME-COURSE OF HEPATITIS-A ANTIBODY-PRODUCTION AFTER ACTIVE, PASSIVE AND ACTIVE-PASSIVE IMMUNIZATION - THE RESULTS ARE HIGHLY DEPENDENT ON THE ANTIBODY-TEST SYSTEM USED

Two commercially available automated test systems for hepatitis A antibody, HAVAB IMX (Abbott) and ENZYMUN Anti-HAV (Boehringer) were evaluated in a study of active, passive and active/passive immunisation against hepatitis A. The inactivated hepatitis A vaccine Epaxal Berna and the hepatitis A immunoglobulin preparation Globuman were products of the Swiss Serum and Vaccine Institute. Although both hepatitis A antibody test kits were standardised with the same international WHO standard hepatitis A immunoglobulin preparation, divergent results were obtained for the level of circulating hepatitis A antibody after vaccination. One month after the vaccination the mean geometric antibody titres were 315 mIU/ml after active, 253 mIU after active/passive and 22 mIU after passive immunisation when measured with the Enzymun assay. In the same sera 70 mIU/ml after active, 60 mIU after active/passive and 18 mIU after passive immunisation could be detected with the IMX test. Antibody avidity studies could not explain the differences obtained by the two test methods. The neutralization test is the standard method for the estimation of protection against hepatitis A. This test is not suitable for large series of serum samples, and enzyme immunoassays are indispensable for vaccination studies. To be suitable for monitoring antibody development in phase I and II clinical trials as well as in postmarketing studies, EIA tests for hepatitis A antibodies must be commercially available and of known sensitivity. The Enzymun anti-HAV test developed by Boehringer Mannheim (Germany) offers the possibility to measure antibody titres around the protective level of 20 mIU/ml which is reached by the passive immunisation with immuoglobulin preparations or within two weeks after active vaccination with an inactivated hepatitis A vaccine. The Abbott IMX test system is more useful for the detection of natural infections by the hepatitis A virus.