97% of the 316 healthy adults still enrolled in the trial retained neutralizing antibody titers above the seroresponse threshold[2] twenty-four months after the single-dose vaccination. The persistence of antibodies in older adults aged 65 and above was as robust as in younger adults and even slightly higher in terms of geometric mean titers and seroconversion rates.

This outcome underscores the vaccine’s potential to offer strong and lasting protection against chikungunya across different age groups.

Study VLA1553-303 collected long-term safety by following any Adverse Event of Special Interest (AESI) from the preceding study and collecting new-onset SAEs.

No safety concerns were identified for the 24-month follow-up, and, as reported in the 12-month data analysis, no AESI was ongoing when participants were enrolled in the trial.