Safety and immunogenicity of Thailand Government Pharmaceutical Organization (GPO) produced, COVID-19 vaccine, 10 μg HXP-GPOVac: A Phase III, double-blind, randomized trial in comparison with VAXZEVRIA

Background HXP-GPOVac is a Thailand-produced, egg-based, inactivated recombinant Newcastle disease virus (NDV)-chimera vaccine expressing a membrane-anchored, prefusion-stabilized SARS-CoV-2 spike (NDV-HXP-S), developed to expand vaccine access. This phase III trial evaluated the safety and immunogenicity of a single HXP-GPOVac dose in healthy or clinically stable Thai adults who had completed a two-dose primary series of an authorized COVID-19 vaccine. Methods In this double-blind, randomized, active-controlled trial in Nakhon Phanom, Thailand, 4000 participants were randomized 3:1 to receive HXP-GPOVac or VAXZEVRIA (AstraZeneca, ChAdOx1 nCoV-19). Safety outcomes included incidence, severity, and vaccine-relatedness of adverse events (AEs). AE incidence was compared between vaccine groups using Chi-square or Fisher's exact test. Immunogenicity was assessed by pseudovirus neutralization assay for 50% neutralizing antibody titers (NT 50 ) and ELISA for anti-Spike IgG. Non-inferiority was prespecified for NT 50 -based endpoints at day 14, defined by (i) a geometric mean concentration (GMC) ratio (HXP-GPOVac/VAXZEVRIA) with 95% CI lower bound >0.67 and (ii) a seroconversion rate (SCR) difference with 95% CI lower bound > −10%. Results Solicited AEs occurred in 43.7% of HXP-GPOVac recipients versus 53.5% of VAXZEVRIA recipients ( p = 0.01). Most solicited AEs were mild. No vaccine-related serious AEs were reported. At day 14, the NT 50 GMC ratio (HXP-GPOVac/VAXZEVRIA) was 0.83 (95% CI lower bound: 0.74), and the SCR difference was −2.35% (95% CI lower bound: −8.72%), both meeting non-inferiority criteria. Conclusion HXP-GPOVac was well-tolerated and demonstrated non-inferior immunogenicity compared with VAXZEVRIA at 14 days after vaccination. These findings provide rationale for larger studies to assess HXP-GPOVac clinical efficacy.