At 43 professional vaccine trial sites in the U.S., the live-attenuated chikungunya vaccine candidate VLA1553 produced a strong immune response and immunoprotective titers in most participants in a placebo-controlled trial, researchers report. Chikungunya virus infections have been reported in more than 100 countries worldwide and is considered a global health threat. These results suggest that “VLA1553 is an excellent candidate for the prevention of disease caused by chikungunya virus,” the authors conclude.
The double-blind phase 3 trial included healthy adults with no history of chikungunya virus infection or immune-mediated or chronic arthritis or arthralgia, known or suspected defect of the immune system, or any inactivated vaccine received within 2 weeks or any live vaccine within 4 weeks before vaccination with VLA1553 or placebo. The primary endpoint was the proportion of baseline negative participants with a seroprotective chikungunya virus antibody level (50% plaque reduction in a micro plaque reduction neutralization test [μPRNT] with a μPRNT50 titer of at least 150) at 28 days after vaccination. Safety was assessed in all participants. Immunogenicity analyses were conducted at 12 predetermined sites.
“Between Sept 17, 2020 and April 10, 2021, 6,100 people were screened for eligibility,” the authors write. “1,972 people were excluded and 4,128 participants were enrolled and randomised (3,093 to VLA1553 and 1,035 to placebo). 358 participants in the VLA1553 group and 133 participants in the placebo group discontinued before trial end. The per-protocol population for immunogenicity analysis comprised 362 participants (266 in the VLA1553 group and 96 in the placebo group). After a single vaccination, VLA1553 induced seroprotective chikungunya virus neutralising antibody levels in 263 (98.9%) of 266 participants in the VLA1553 group (95% CI 96.7–99.8; P <0.0001) 28 days post-vaccination, independent of age. VLA1553 was generally safe with an adverse event profile similar to other licensed vaccines and equally well tolerated in younger and older adults. Serious adverse events were reported in 46 (1.5%) of 3,082 participants exposed to VLA1553 and eight (0.8%) of 1,033 participants in the placebo arm. Only two serious adverse events were considered related to VLA1553 treatment (one mild myalgia and one syndrome of inappropriate antidiuretic hormone secretion). Both participants recovered fully.”