Study on the Persistence of Immunity Following EV71 Vaccination

The initial study was a randomized, double-blind, placebo-controlled phase III clinical trial conducted in children aged 6-71 months from Guilin region of Guangxi Province in 2012. A total of 12000 participants (with 1100 in the immunogenicity group) were randomized in a 1:1 ratio to receive two doses EV71 vaccine or placebo on a 0-, 28-day schedule. Besides, an extended one-year and two year follow-up of this study was completed in 2013.

In this study, immunogenicity group participants from the phase III clinical trial was chosen as the studied subjects. A retrospective survey for the enrolled subjects involved with the history of HFMD and the extra vaccination of EV71 vaccine was conducted before blood collection. 3 ml venous blood were collected from each available subject for EV71 neutralizing antibody (NAb) testing. Since the unblinding was performed after the initial study completed, this study was an open-labelled detection for the persistence of the vaccine-induced EV71 NAb.

Inclusion criteria

• Included in the immunogenicity group of initial studyand randomly into either vaccine (fulfilled the two doses vaccination following the protocol) or placebo group.
• Volunteers and their legal guardians or appointed representatives must provide valid legal identification documents.
• Legal guardians or appointed representatives of volunteers must have the capacity to understand the informed consent document and the research process, voluntarily participate, sign the informed consent form, and be able to comply with the study's requirements.

Exclusion criteria

• Had history of extra EV71 vaccination.
• Previous history of hand-foot-mouth disease.
• Participating in other research.
• Subjects with a hereditary bleeding tendency or coagulopathy, or a history of bleeding disorders.
• Investigators' Discretion: The final exclusion criterion is the discretion of investigators to determine whether a subject is suitable for participation in the study.