These data demonstrate the efficacy of vapor heating in inactivating high-titer HAV after the spiking of plasma products with virus. This study confirms and explains the results of controlled clinical trials and long-term clinical usage with respect to the lack of HAV transmission by such vapor-heated products.

The transmission of hepatitis A virus (HAV) associated with use of FVIII concentrates has been reported in a number of European countries. All of these cases were associated with products inactivated by use of solvent detergent treatment. These reports have emphasized the necessity of evaluating virus inactivation methodologies for their ability to inactivate HAV. Such studies had previously been hampered by the difficulties associated with titration of HAV, because of the minimal cytopathic effect of most strains of virus on tissue culture cells. We have developed a simple, rapid, TCID50 virus titration system using a cytopathic strain of HAV which allows extensive kinetic studies of HAV inactivation. This has been compared with the standard radioimmunofocus forming (RFF) assay which is presently used for HAV titration. The reproducibility of the TCID50 assay was demonstrated to be equal to that of the RFF assay and the 95% confidence intervals for titres determined by both assays were also equal. The thermal stability of the cytopathic strain was studied and shown to be equivalent to that of a noncytopathic strain. The kinetics of HAV inactivation by heating in aqueous solution were compared to those of HIV-1 and a number of model viruses. It was demonstrated that HAV was highly stable, with 5 hours heat treatment at 60 degrees C in aqueous solution being required to inactivate 5.8 log10 virus. In contrast to heating in aqueous solution, lyophilization followed by 1 hour vapor heating at 60 degrees C was sufficient to inactivate 5.9 log10 HAV.