Preliminary results from the ongoing phase III trial of the single dose live-attenuated chikungunya vaccine (VLA 1553) show robust protection against the chikungunya virus and no safety concerns, according to a study presented at the 2021 annual meeting of the American Society of Tropical Medicine & Hygiene (ASTMH), which was held virtually. The immunogenicity and safety profile were comparable across all ages studied in the trial.

The multicenter trial enrolled 4115 adults in the United States; of these, 3652 were 18-64 years old, while 463 were aged 65 years and older. 3082 participants were given one vaccine dose, while 1033 received the placebo. The percentage of participants with seropositive neutralizing antibody titers 28 days after receiving the vaccine was taken as the primary outcome measure. All participants were seronegative at baseline.

The high immunogenicity of the vaccine candidate was evident by the 64-fold rise in the level of neutralizing antibodies on the 29th day, after a single injection, in a subgroup of 264 of the 268 participants evaluated. The 98.5% seroprotection rate is much higher than the cut-off of 70% (for non-acceptance) agreed with the US FDA for licensing of the vaccine. The side effects reported included headache, fatigue, myalgia, tenderness at the site of injection. These were mild or moderate in nature suggesting that the vaccine was also well tolerated. Three study subjects reported severe fever.

VLA1553 was accorded the “Breakthrough Therapy” status from the US FDA in July this year.

Final data from the phase III trial is expected in six months.

Reference

1. Jaramillo JC, et al. Chikungunya: Phase 3 Clinical Development of a Single-shot Live-attenuated Vaccine. ASTMH 2021; Abstract 0848.