WHO/BS/2017.2308 Collaborative Study to Evaluate the Proposed 3rd WHO IS for Hepatitis A Virus (HAV) for Nucleic Acid Amplification Technology (NAT)-Based Assays

Overview

This report describes the preparation and collaborative study evaluation of the replacement 3rd WHO International Standard for Hepatitis A virus (HAV) for use in the standardisation of nucleic amplification techniques (NAT). Two freeze dried candidates were evaluated alongside the current 2nd WHO International Standard for HAV (NIBSC code 00/562). Both candidates are lyophilised preparations comprising HAV RNA positive plasma diluted in pooled human plasma with one batch also containing stabilizing excipients, hepes buffer and trehalose. In this collaborative study eleven laboratories from ten countries participated to evaluate suitability and potency of both candidates using their routine HAV NAT assays. Replacement candidates were evaluated alongside two HAV RNA positive plasma samples. Participating laboratories used a range of real-time PCR technology based NAT assays, the majority being commercial qualitative assays. Variability in reported laboratory mean estimates for samples 1-3 was higher for qualitative assays (SD of 0.38 to 0.51 Log10 NAT-detectable units) compared to quantitative assays (SD of 0.18 to 0.31 Log10 IU/mL). Agreement between laboratories improved when potencies were expressed relative to the 2nd WHO International Standard for HAV (sample 1). Replacement candidate samples 2 and 3 overall mean potency estimates from qualitative and quantitative assays, relative to 2nd WHO International Standard for HAV were 4.42 and 4.53 Log10 IU/mL respectively. For samples 1-3 a discrepancy (of ~ 0.4 Log10) in reported laboratory mean estimates between qualitative and quantitative assays was observed, as with similar observations in previous replacement studies reasons for this remain unclear.