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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.

Kriengkrai Prasert S. Nakphook Jiraphut Kittiwatanachod Darunee Ditsungneon K. Sornwong S. Naosri Ponthip Wirachwong I. Techatanawat P. Narakorn S. Surichan Jorge Flores L. D. Mercer Christina S. Polyak Bruce L. Innis R. Raghunandan C. Pittayawonganon S. Iamsirithaworn S. Sirilak Colleen Scott M. P. Montgomery William W. Davis P. Praphasiri

Oct 2026 · Vaccine · Vol 94, pp. 129230 · 0 citations · 23 references

Medicine

Abstract

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 (NT50) and ELISA for anti-Spike IgG. Non-inferiority was prespecified for NT50-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 NT50 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.

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