Valneva’s next-gen Zika vaccine shows strong safety and immune response in phase I trial

VLA1601 is a purified and inactivated vaccine specifically designed to protect against the Zika virus

Valneva announced positive topline results from a Phase I clinical trial evaluating its second-generation Zika vaccine candidate, VLA1601. The trial demonstrated that the vaccine was generally well tolerated and safe, while also showing strong immunogenicity across all tested groups.

VLA1601 is a purified and inactivated vaccine specifically designed to protect against the Zika virus (ZIKV). The controlled, randomized Phase I study enrolled approximately 150 healthy adults aged 18 to 49 years in the United States.

Participants received two doses of the vaccine, administered four weeks apart, in varying dose levels—low, medium, and high—with aluminium as an adjuvant. The study also evaluated two additional adjuvants—3M-052-AF (Access to Advanced Health Institute) and CpG1018 (Dynavax Technologies)—combined with the low-dose formulation.

Data collected up to day 57 after the second dose confirmed that VLA1601 was well tolerated, with no safety concerns identified across any of the five treatment groups. An independent Data Safety Monitoring Board further validated the vaccine’s favourable safety profile.

Immunogenicity results revealed that all vaccine formulations elicited strong neutralising antibody responses, with the double-adjuvant combinations (low dose with alum and either CpG1018 or 3M-052-AF) achieving statistically higher neutralising antibody titres on days 43 and 57 compared to the single-adjuvant arm. The vaccine achieved a peak geometric mean fold increase in antibody titres of over 56-fold and a seroconversion rate above 93 per cent, demonstrating improved immune responses compared to Valneva’s first-generation candidate, whose Phase I results were reported in 2018.

VLA1601 leverages Valneva’s established manufacturing platform used for its licensed Japanese encephalitis vaccine, IXIARO.

Juan Carlos Jaramillo, M.D., Chief Medical Officer of Valneva, commented: “We are pleased by the notable safety and immunogenicity results demonstrated for our Zika vaccine candidate, particularly the promising data from our double-adjuvanted formulations. As global temperatures rise and rainfall patterns shift, the expanding habitats of disease-carrying mosquitoes continue to heighten public health risks for infections such as Zika.”

Valneva continues to advance its portfolio of vaccines against mosquito-borne diseases. In June 2025, the company also reported encouraging six-month safety and antibody persistence data from the Phase II trial of its chikungunya vaccine, IXCHIQ, in 304 healthy paediatric participants aged one to eleven years.