Breakthrough in Chikungunya Prevention: VLA1553 Vaccine Induces Robust Immune Response

Chikungunya virus is a vector-borne disease transmitted by the bite of an infected mosquito. With sporadic, unpredictable outbreaks, chikungunya virus is a threat to global health.

The US Centers for Disease Control and Prevention (CDC) reports the most common symptoms of chikungunya are fever and joint pain, but other common symptoms may include headache, rash, joint swelling, or muscle pain. Chikungunya outbreaks have occurred around the world, though infections are most common in Africa, Asia, and the Indian subcontinent.

At least 5 million chikungunya virus infections were reported over the last 15 years, and increasing international travel means cases will likely increase. The virus can be spread by infected travelers, and there is currently no vaccine to prevent or treat infection with the chikungunya virus.

However, there is a new vaccine candidate on the rise. A recent phase 3 trial assessed the safety and immunogenicity of VLA1553, a live-attenuated vaccine designed to combat chikungunya virus disease. The results, published in The Lancet, reveal VLA1553 induced a robust immune response and seroprotective titers in almost all vaccinated participants.

The double-blind, multicenter, randomized study was conducted in 43 vaccine trial sites across the United States. A total of 6100 potential adult participants were screened between September 17, 2020 and April 10, 2021, with 4128 meeting eligibility criteria.

Participants were randomized into 2 groups, with 3093 receiving VLA1553 and 1035 receiving placebo. Before the trial ended, 358 participants in the VLA1553 group and 133 in the placebo group discontinued treatment.

After a single vaccination, VLA1553 demonstrated remarkable efficacy, inducing seroprotective chikungunya virus neutralizing antibody levels in 98.9% of participants within 28 days, irrespective of age.

The vaccine's safety profile was comparable to approved vaccines, and younger and older adults tolerated it equally well. Out of the total participants, 362 individuals were included in the per-protocol population for immunogenicity analysis. Only 1.5% of the cohort experienced serious adverse events, with the majority having no relation to the vaccine. In the placebo group, 0.8% reported serious adverse events.

Two cases—a mild myalgia and a syndrome of inappropriate antidiuretic hormone secretion—were considered potentially associated with VLA1553, but both individuals made a full recovery.

This study is limited in that it did not take place in a region where chikungunya virus is endemic. Additionally, the VLA1553 is based on a live, attenuated virus platform, likely rendering it unusable in severely immunocompromised individuals.

However, by inducing sustained seroprotective levels of antibodies in 98.9% of participants up to 180 days after vaccination, VLA1553 met its primary endpoint. These findings suggest that VLA1553 holds immense promise, concluded the study authors, writing, “The generation of protective titers in virtually all vaccinated participants independent of age positions VLA1553 as an excellent candidate for the prevention of chikungunya.”