WHO/BS/2014.2241 Collaborative Study to Evaluate the Candidate 3rd WHO IS for Hepatitis B Surface Antigen

Overview

A WHO international collaborative study was undertaken to characterize and assess the suitability of a candidate replacement WHO International Standard (IS) for HBsAg for use in the standardization of HBsAg assays. The candidate is a non-adjuvanted, plasma-derived HBsAg vaccine bulk formulated to give ~ 50 International Units (IU)/mL in thrombinized and declotted plasma, dispensed into ampoules in 1.0 mL aliquots and freeze-dried for long-term stability. The candidate antigen is hepatitis B virus (HBV) genotype B4 with a heterogeneous HBsAg subtype population of ayw1 and adw2.

Twelve laboratories from 9 countries participated in the collaborative study to evaluate the fitness for purpose and potency of the candidate using their routine assays for HBsAg. The freeze-dried candidate 3rd WHO IS (NIBSC code 12/226) was evaluated alongside the 2nd WHO IS for HBsAg (NIBSC code 00/588) and the 1st WHO IS for HBsAg (NIBSC code 80/549). Blinded study samples were also provided for testing in the collaborative study. These included a duplicate of the candidate 3rd IS, a negative control and samples representing different HBV genotypes.

In this collaborative study, a range of commercial qualitative and quantitative HBsAg tests were used to evaluate the candidate IS. The overall geometric mean potency of the candidate, plus its coded duplicate, relative to the concurrently tested 2nd IS for HBsAg was 47.3 IU/mL, a value that is very close the target 50 IU/mL Laboratories showed a generally good level of reproducibility for each kit. Intra-laboratory agreement generally was better than the interlaboratory agreement. Some HBV genotype-dependent effects on the inter-laboratory variability were observed with variability between laboratories being greatest for samples more distantly related to the reference standard. The results obtained from accelerated thermal degradation studies at ~1 year indicate that the candidate is stable and suitable for long-term use.

The results of the collaborative study indicate the suitability of the candidate to serve as an IS and it is proposed that 12/226 is established as the 3rd WHO IS for HBsAg with an assigned potency of 50 IU when reconstituted in 1 mL water