French vaccine company Valneva SE (Nasdaq:VALN) (Euronext Paris:VLA) on Tuesday reported sustained antibody responses five years after a single dose of its chikungunya vaccine, IXCHIQ, with 94% of 221 evaluable participants maintaining neutralising antibody levels above the seroresponse threshold.

The five-year results demonstrated comparable antibody persistence among adults aged 65 and older and those aged 18 to 64, further supporting the vaccine's potential to provide long-term protection following a single vaccination.

The VLA1553-303 trial, supported by the Coalition for Epidemic Preparedness Innovations (CEPI) and the European Union's Horizon Europe programme, will continue monitoring participants for up to ten years to assess long-term immune response durability.

Valneva is also generating real-world evidence through post-marketing initiatives, including Brazil's first large-scale public vaccination campaign using IXCHIQ. Conducted between February and October 2026 by Brazil's Ministry of Health and Instituto Butantan, with Valneva's support, the campaign vaccinated nearly 80,000 adults aged 18 to 59.

The ongoing post-marketing studies are expected to provide further effectiveness and safety data, supporting the assessment of IXCHIQ's public health value.