An Extension Study of EV-BR1701 Part A1

Long-Term Immunogenicity Study of an Adjuvanted Inactivated Enterovirus 71 (EV71) Vaccine in Healthy Infants and Children: An Extension Study of EV-BR1701 Part A1

To determine the long-term immunogenicity more than 5 years after EnVAX-A71 vaccination in the pediatric population aged 2 months to <6 years when first vaccinated.

Study Overview

• Status: Completed
• Conditions: Enterovirus Infections

Detailed Description

I. Study Design:

EV-BR1701 was a randomized, multi-nation, multi-centered, double-blinded, phase III study to evaluate the efficacy and safety of an EV71 vaccine, EnVAX-A71, in healthy infants and children in Taiwan (Part A) and Vietnam (Part B). In both Parts, a sub-study for immunogenicity assessment for up to one year was performed. This extension study of EV-BR1701 aims to evaluate the long-term immunogenicity persistence more than 5 years after EnVAX-A71 vaccination in subjects originally participating in the immunogenicity sub-study in Taiwan.

The evaluable subjects of EV-BR1701 Part A1(immunogenicity sub-study), who were aged 2 months to < 6 years when entering the main study and completed two injections of either EnVAX-A71 or placebo with evaluable data for the primary immunogenicity endpoint, will be recalled to enter this extension study for phlebotomy and immunogenicity analysis. These subjects will not receive further vaccination according to this extension study protocol.

The principal investigators (PIs) and study coordinators (SCs) of the original medical center will contact the subject's guardians/legal representative by phone to return to the medical center for phlebotomy. Informed consent will be provided to the guardian/legal representative of the subjects, and the eligibility of subjects will be verified on the day of the recall visit.

After the subject is evaluated by the PI and meets the phlebotomy requirements, the subject's guardian/legal representative will be asked to sign the informed consent form, and the subject will be given the same identifier as what he/she was originally assigned in the main study for continuity of his/her immunogenicity data.

About 3-4 mL of blood will be collected from each subject, and the serum will be collected and sent to the designated central laboratory for testing. The validated neutralizing antibody (NTAb) analysis method will be used to determine the EV71-specific neutralizing antibody titer. The NTAb titer results will be directly sent to the CRO Data Management Team, and statistical analysis for immunogenicity will be performed and reported.

• Study Type: Observational
• Enrollment (Actual): 180

Contacts and Locations

Study Locations

• Taiwan
  • Hsinchu, Taiwan
    • National Taiwan University Hospital HsinChu Branch
  • Taichung, Taiwan
    • China Medical University Hospital
  • Taipei, Taiwan
    • National Taiwan University Hospital
  • Taoyuan, Taiwan
    • Linkou Chang Gung Memorial Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child
• Accepts Healthy Volunteers: N/A

• Sampling Method: Non-Probability Sample

Study Population

EV-BR1701 was a randomized, multi-nation, multi-centered, double-blinded, phase III study to evaluate the efficacy and safety of an EV71 vaccine, EnVAX-A71, in healthy infants and children in Taiwan (Part A) and Vietnam (Part B). In both Parts, a sub-study for immunogenicity assessment for up to one year was performed. This extension study of EV-BR1701 aims to evaluate the long-term immunogenicity persistence more than 5 years after EnVAX-A71 vaccination in subjects originally participating in the immunogenicity sub-study in Taiwan.

Description

Inclusion Criteria:

1. Healthy children who were enrolled in Part A1 (immunogenicity sub-study) of EV-BR1701, received two injections of either EnVAX-A71 or placebo, and had blood sample collected on Day 56 for primary immunogenicity endpoint analysis (the "evaluable" subjects).
2. The subject's guardian/legal representative is able and willing to comply with study procedures and provide signed informed consent.

Exclusion Criteria:

1. History of bleeding disorder, hemostatic difficulties or significant bruising caused by phlebotomy since the last visit in EV-BR1701 main study.
2. Having been vaccinated with any EV71 vaccine products.

Study Plan

How is the study designed?

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
The long-term immunogenicity of EnVAX-A71 on the seroconversion rate (SCR)	SCR (seroconversion rate) is defined as the percentage of subjects achieving either a pre-vaccination neutralizing antibody titer <1:8 and a post-vaccination neutralizing antibody titer ≥1:32, OR a pre-vaccination neutralizing antibody titer ≥1:8 and a minimum 4-fold increase in post-vaccination neutralizing antibody titer.	From Sep-2025 to Dec-2025
The long-term immunogenicity of EnVAX-A71 on SPR	SPR (seroprotection rate, the proportion of the subjects with NTAb against EV71 titer ≥1:32)	From Sep-2025 to Dec-2025
The long-term immunogenicity of EnVAX-A71 on the geometric mean titer (GMT) and geometric mean titer ratio (GMTR) of EV71 neutralizing antibody (NTAb)	GMTR (geometric mean titer ratio) is defined as the GMT at the recall visit divided by the GMT at pre-vaccination (Day 0 of main study).	From Sep-2025 to Dec-2025

Collaborators and Investigators

• Sponsor: Enimmune Corporation
• Investigators: Study Director: Wendy Wu, Enimmune Corporation

Study record dates

Study Major Dates

• Study Start (Actual): September 20, 2025
• Primary Completion (Actual): December 27, 2025
• Study Completion (Actual): April 22, 2026

Study Registration Dates

• First Submitted: May 28, 2026
• First Submitted That Met QC Criteria: June 3, 2026
• First Posted (Actual): June 9, 2026

Study Record Updates

• Last Update Posted (Actual): June 9, 2026
• Last Update Submitted That Met QC Criteria: June 3, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Infections; RNA Virus Infections; Virus Diseases; Picornaviridae Infections; Enterovirus Infections
• Other Study ID Numbers: EV-BR1701 Part A1 Extension

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No