United States-based VBI Vaccines has revealed top-line data from CONSTANT, the second pivotal Phase three study, evaluating lot-to-lot manufacturing consistency of Sci-B-Vac, the company's trivalent hepatitis B (HBV) vaccine, and comparing safety and immunogenicity of Sci-B-Vac to United Kingdom-based GlaxoSmithKline's presently-marketed HBV vaccine, Engerix-B, it was reported on Friday.

The Phase three study enrolled 2,838 adults aged 18 to 45 years and met both the primary and secondary endpoints.

The primary endpoint of the study was lot-to-lot consistency for immune response, as measured by geometric mean concentration of antibodies across three independent, consecutively-manufactured lots of Sci-B-Vac, four weeks after the third vaccination. Along with the positive safety and immunogenicity results of the PROTECT Phase three study, these data include the basis for the regulatory submissions in the United States, Europe, and Canada, likely to start in the second half of 2020.

A secondary endpoint of the study was non-inferior immunogenicity as measured by sero protection rates at day 196, one month after completion of the complete course of vaccination with either Sci-B-Vac or Engerix-B. At day 196, the pooled sero protection rates in subjects who received Sci-B-Vac was 99.3% compared to 94.8% for those who received Engerix-B – a difference of 4.49%; 95% Confidence Interval (CI) [2.90%, 6.63%] – up from 90.4% for Sci-B-Vac and 51.6% for Engerix-B at day 168, after only two vaccinations. In addition to showcasing non-inferiority, the sero protection rates achieved with Sci-B-Vac compared with Engerix-B was higher after both two and three vaccinations.

The safety and tolerability seen in CONSTANT were consistent with the known safety profile of Sci-B-Vac. No new safety risks were identified and no safety signals were observed in either cohort. The integrated safety data analysis from both the PROTECT and CONSTANT studies is underway.