Harmonization of Zika neutralization assays by using the WHO International Standard for anti-Zika virus antibody

Abstract

During outbreaks of emerging viruses, such as the Zika outbreak in 2015-2016, speed and accuracy in detection of infection are critical factors to control the spread of the disease; often serological and diagnostic methods for emerging viruses are not well developed and validated. Thus, vaccines and treatments are difficult to evaluate due to the lack of comparable methods. In this study, we show how the 1st WHO International Standard for anti-Zika antibody was able to harmonize the neutralization titres of a panel of serological Zika-positive samples from laboratories worldwide. Expression of the titres in International Unit per millilitre reduced the inter-laboratory variance, allowing for greater comparability between laboratories. We advocate the use of the International Standard for anti-Zika virus antibodies for the calibration of neutralization assays to create a common language, which will permit a clear evaluation of the results of different clinical trials and expedite the vaccine/treatment development.

Keywords: Policy and public health in microbiology; Viral infection.

Fig. 1

Harmonization of the samples’ potency when reported as relative to the candidate International Standard. a The geometric mean of neutralization titres for each sample as reported by the participants following three independent experiments (Table 3) are plotted; b neutralization titres were calculated relative to the candidate International Standard (sample S80), assuming an arbitrary value of 1000 IU/mL (Table 4). Samples S2, S6, and S38 are the negative controls; samples S53, S79, and S93 are the anti-dengue serum samples

Fig. 2

ELISA potencies calculated relative to the candidate International Standard. The samples were analysed using commercial and in-house quantitative assays as described in Table 6. The potencies in IU/mL were calculated from the geometric mean of three independent assays of the data expressed relative to the value of sample S80, which was assigned an arbitrary value of 1000 IU/mL Only the estimates calculated for labs 2c and 4 were valid by parallel line analysis

Fig. 3

Thermal degradation assessment of the candidate International Standard for ZIKV antibody. Freeze-dried ampoules of sample S80 (NIBSC code 16/352) were stored at five different temperatures (45, 37, 20, 4, and −20 °C). At each time point, three vials were retrieved and reconstituted with 0.25 mL of molecular grade water. Each vial was assessed in triplicate in the in-house ELISA. Data are reported relative to the storage temperature −20 °C; a the graph shows the variation in potency against time; b the bottom table contains the mean value of three independent experiments of the relative potency with the 95% confidence limit within parentheses