Collaborative study to evaluate a candidate World Health Organization International Standard for Zika virus for Nucleic Acid Amplification Technique (‎NAT)‎-Based assays

Overview

The aim of the collaborative study was to assess the suitability of a candidate International Standard (IS) for Zika virus (ZIKV) for nucleic acid amplification technique (NAT)-based assays. Potency of the candidate IS and related reference preparations was evaluated using a range of NAT-based assays for ZIKV RNA with the aim of assigning an internationally agreed unitage to the candidate WHO IS.

The candidate IS consisted of an inactivated, lyophilized ZIKV preparation formulated in a stabilizing, neutral solution and intended for dilution using a range of different types of sample matrix. The virus strain used for the preparation of the candidate IS originated from a ZIKVinfected patient from French Polynesia, closely related to ZIKV strains currently circulating in the Asia-Pacific region and central and South America. Further strains from the Asian ZIKV lineage were included in the study as well as two preparations derived from African ZIKV isolates.

The samples consisted of a mixture of inactivated ZIKV reference materials as well as clinical materials (urine or plasma) from ZIKV-infected patients. In addition, a panel of in vitro transcribed RNAs covering partial ZIKV genome sequences were included in the study. The samples for evaluation were distributed to 24 laboratories from 11 different countries. The samples were assayed on three separate days and the data were collated and analysed at the PaulEhrlich-Institut (PEI). Data were returned by 21 of the participating laboratories, in total 37 sets of data were analysed; 19 from quantitative assays and 18 from qualitative assays. The assays used consisted of a mixture of in-house developed and commercial assays (currently available or in development). The results showed that all samples were detected consistently by the majority of participants. The candidate standard is very stable under recommended storage conditions, i.e. at or below -20ºC, and is therefore suitable for long term use. On-going real-time and accelerated stability studies of the candidate IS are in progress.

It is proposed that the heat-inactivated and lyophilized preparation with cell culture-derived French Polynesian ZIKV strain be established as the 1st IS for ZIKV RNA with an assigned unitage of 50,000,000 International Units per ml.