Persistence of Immunogenicity of a Purified Inactivated Zika Virus Vaccine Candidate in Healthy Adults: 2 Years of Follow-up Compared With Natural Infection.

Background: We report 2-year persistence of immune response to Takeda's prophylactic purified formalin-inactivated whole Zika virus vaccine candidate (TAK-426) compared with that observed after natural infection.

Methods: A randomized, observer-blind, placebo-controlled, dose-selection, phase 1 trial was conducted in 18-49-year-old adults at 9 centers (7 in the United States, 2 in Puerto Rico) from 13 November 2017 to 24 November 2020. Primary objectives were safety, tolerability, and immunogenicity of 3 increasing doses of TAK-426 administered as 2 doses 28 days apart to flavivirus (FV)-naive and FV-primed adults. Here, we report on safety and persistence of immunity up to 2 years after primary vaccination with 10-μg TAK-426, the highest dose, and compare neutralizing antibody responses with those observed after natural infection.

Results: TAK-426 at 10-μg had an acceptable safety profile in FV-naive and FV-primed adults up to 24 months after dose 2. Seropositivity for neutralizing antibodies was 100% at 1 year, and 93.8% and 76.2% at 2 years in FV-naive and FV-primed groups, respectively. TAK-426 responses were comparable in magnitude and kinetics with those elicited by natural Zika virus infection.

Conclusions: These results support the further clinical development of TAK-426 for both FV-naive and FV-primed populations.

Clinical Trials Registration: NCT03343626.