Establishing China's National Standard for the Recombinant Adenovirus Type 5 Vector-Based Ebola Vaccine (Ad5-EBOV) Virus Titer

The 2014 Ebola outbreak in West Africa brought great threat to public health worldwide. There was no approved antiviral therapy or vaccine available to control the disease at that time. Several kinds of Ebola vaccines were urgently under development across the world. Among these, the novel recombinant adenovirus type 5 vector-based Ebola vaccine (Ad5-EBOV)-the first Ebola vaccine based on the 2014 Zaire Guinea epidemic strain-was developed in China, and its safety and immunogenicity were demonstrated in China and Sierra Leone. The license to market the drug was approved on October 19, 2017, by the Chinese Food and Drug Administration. In order to standardize the test on the Ad5-EBOV virus titer, China's national standard substance for the virus titer of Ad5-EBOV was established according to the recommendations for the preparation, characterization, and establishment of international and other biological reference standards from the World Health Organization and Chinese Pharmacopoeia (third edition). The standard for the Ad5-EBOV virus titer was prepared with a volume of 0.5 mL per ampoule in lyophilized form. The samples of the standard, designated as A, B, C, D with different aims, were blinded and distributed to five laboratories to be collaboratively calibrated. The virus titer for this standard was determined with the antibody staining method according to the instructions in the Adeno-X (TM) Rapid Titer Kit. The homogeneity and stability of the standard substance were also satisfied. The virus titer standard value was 8.54 lg infectious units (IFU)/mL, and the 95% confidence interval was between 7.94 lg IFU/mL and 9.14 lg IFU/mL. This standard was approved by the Chinese national committee and is available on the National Institutes for Food and Drug Control Web site (www.nifdc.org.cn; lot no. 250019-201501).