Valneva Reports Positive Phase 1 Results for Second-Generation Zika Vaccine Candidate VLA1601

October 2025 – Saint-Herblain, France: Valneva SE, a specialty vaccine company, has reported positive results from its Phase 1 clinical trial evaluating VLA1601, its second-generation inactivated, adjuvanted vaccine candidate targeting the Zika virus (ZIKV). The trial demonstrated a favorable safety profile and strong immunogenicity, particularly in formulations incorporating a double-adjuvant system.

Study Design and Safety Results

The randomized, controlled Phase 1 trial (VLA1601-102) enrolled around 150 healthy adults aged 18 to 49 in the United States. Participants received two doses, administered four weeks apart, of either a low, medium, or high antigen dose of the aluminum-adjuvanted vaccine. The low-dose formulation was also tested with additional adjuvants — CpG 1018 (Dynavax Technologies Corporation) and 3M-052-AF (Access to Advanced Health Institute).

Results through Day 57 (four weeks post-second dose) showed that VLA1601 was safe and well tolerated across all five treatment arms. No serious adverse events or safety concerns were identified, and an independent Data Safety Monitoring Board confirmed the absence of safety issues.

Enhanced Immune Response

All treatment arms generated detectable immune responses, with the strongest responses observed in the double-adjuvanted formulations (Low + Alum + 3M-052-AF and Low + Alum + CpG1018). These groups demonstrated significantly higher neutralizing antibody titers compared with the alum-only group.

Immunogenicity also improved compared with Valneva’s first-generation Zika vaccine tested in 2018, with:

• Seroconversion rates exceeding 93% (vs. 86% previously)
• Geometric Mean Fold Increase >56 (vs. >7 previously)

The data indicate that combining aluminum with an additional adjuvant enhances both antibody magnitude and durability.

Platform and Broader Implications

VLA1601 was developed using Valneva’s inactivated vaccine platform, originally employed for its licensed Japanese encephalitis vaccine (Ixiaro) and later optimized for its COVID-19 vaccine (VLA2001).

“We are pleased by the notable safety and immunogenicity results demonstrated for our Zika vaccine candidate and especially our double-adjuvantation results,” said Dr. Juan Carlos Jaramillo, Chief Medical Officer of Valneva. “As global temperatures rise and mosquito habitats expand, the risk of infections such as Zika continues to grow.”

Despite these promising results, Valneva noted that further development will depend on external funding, given uncertainties surrounding regulatory pathways and market demand for Zika vaccines.

Zika Virus Background

The Zika virus, a mosquito-borne flavivirus discovered in 1947, has caused multiple outbreaks across Africa, Asia, the Pacific, and the Americas. It remains endemic in 89 countries and territories, primarily in tropical and subtropical regions.

According to the World Health Organization (WHO), Zika infection is linked to congenital microcephaly and Guillain-Barré syndrome (GBS). Since 2013, 31 countries have reported congenital cases associated with the virus.

About Valneva

Valneva SE is a specialty vaccine company focused on the development, manufacturing, and commercialization of prophylactic vaccines targeting infectious diseases with unmet medical needs. The company leverages its expertise across multiple vaccine platforms to deliver first-, best-, or only-in-class preventive solutions.

Optimize Your trial insights with Clival Database.

Are you exhausted from the uncertainty of trial insights pricing? Clival Database ensures the clarity in the midst of the global scenario for clinical trials to you.

Clival Database is one of the best databases that offers an outstanding number of clinical trial data in terms of 50,000+ molecules and from primary regulatory markets as well as new entrants like Indian and Chinese markets.

With Clival, you get accurate positioning of historical sales data, patent database, company profiling, safety & efficacy, and prediction of launch of new innovative molecules helping you to align your research and driving down the cost.

To add value, we further break down our analytics for you so that improving your operational effectiveness; optimizing your clinical trials; and offering you accurate and high-quality data at lowest possible prices becomes possible.

Elevate your trial success rate with the cutting-edge insights from Clival database.

Check it out today and make more informed sourcing decisions! Learn More!