**Yike Li 1, Xiaofen Huang 1, Zhigang Zhang 1, Shaowei Li 1,2, Jun Zhang 1, Ningshao Xia 1,2 and Qinjian Zhao 1,\***


Received: 10 December 2019; Accepted: 13 January 2020; Published: 16 January 2020

**Abstract:** Hepatitis E virus (HEV) infection causes sporadic outbreaks of acute hepatitis worldwide. HEV was previously considered to be restricted to resource-limited countries with poor sanitary conditions, but increasing evidence implies that HEV is also a public health problem in developed countries and regions. Fortunately, several vaccine candidates based on virus-like particles (VLPs) have progressed into the clinical development stage, and one of them has been approved in China. This review provides an overview of the current HEV vaccine pipeline and future development with the emphasis on defining the critical quality attributes for the well-characterized vaccines. The presence of clinically relevant epitopes on the VLP surface is critical for eliciting functional antibodies against HEV infection, which is the key to the mechanism of action of the prophylactic vaccines against viral infections. Therefore, the epitope-specific immunochemical assays based on monoclonal antibodies (mAbs) for HEV vaccine antigen are critical methods in the toolbox for epitope characterization and for in vitro potency assessment. Moreover, serological evaluation methods after immunization are also discussed as biomarkers for clinical performance. The vaccine efficacy surrogate assays are critical in the preclinical and clinical stages of VLP-based vaccine development.

**Keywords:** antigenic analysis; epitope characterization; hepatitis E vaccine; serological evaluation; virion-like epitopes; well-characterized vaccines
