Zika Virus Vaccine Candidate Confers Robust Immunity Among Healthy Adults

Zika virus vaccine candidate TAK-426 is safe, immunogenic, and well-tolerated among both flavivirus-naive and flavivirus-primed populations. These study results were published in The Journal of Infectious Diseases.

This randomized, observer-blinded, placebo-controlled, dose-selection phase 1 trial was conducted at 9 centers across the United States and Puerto Rico between November 2017 and November 2020. Two doses of TAK-426, a purified formalin-inactivated whole Zika virus vaccine, were administered 28 days apart to adults aged 28 to 49 years. Participants were randomly assigned in a 1:1:1:1 fashion to receive either low-, medium-, or high-dose vaccination, or placebo. Each cohort consisted of an equal number of flavivirus-naive and flavivirus-primed participants. The primary objective was to determine the safety, tolerability, and immunogenicity of TAK-426. Patients in the low- and medium-dose cohorts were observed up to 6 months, and those in the high-dose cohort were observed for 2 years.

There were 125 flavirus-naive and 146 flavivirus-primed participants among the 4 cohorts. Overall, the mean participant age was 35.5 years, 58% were women, and 72% were aged 30 to 49 years.

Two months following vaccination, seropositivity rates were robust among flavivirus-naive (100%) and flavivirus-primed (99%) participants. Seropositivity among flavivirus-naive participants in each cohort was maintained through 8 months. A seropositivity rate of 100% was observed through 14 months among flavivirus-naive participants in the high-dose cohort, followed by a decrease to 93.8% at 26 months. Of flavivirus-primed participants in the high-dose cohort, all maintained a seropositivity rate of 100% through 14 months, though 76.6% remained at this rate through 26 months.

Among flavivirus-naive participants in the placebo cohort, seronegativity was maintained through 14 months. Of 19 participants who were initially naive to flavivirus, 5 seroconverted at 26 months, suggesting natural infection or infection due to another flavivirus with stimulation of cross-reactive antibodies.

There were no deaths, hospitalizations, or vaccine-related severe adverse events reported within the 24-month follow-up period. Two pregnancies were reported, with no adverse effects noted in the newborns.

According to the researchers, “Further studies will also be needed to evaluate the safety of the vaccine in dengue-endemic areas.”

Disclosures: This research was supported by Takeda Vaccines, Inc. Some authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.