The hepatitis E virus (HEV) is among the leading global causes of acute viral hepatitis. Molecular studies of HEV strains have identified four main genotypes. Genotypes 1 and 2 are limited to humans and are transmitted through contaminated water in resource-limited countries, mainly in Asia. Genotypes 3 and 4 are zoonotic, causing sporadic indigenous hepatitis E in nearly all countries.
Each year, approximately 20 million HEV infections occur worldwide, resulting in around 3.3 million symptomatic infections and 70,000 deaths. Despite this toll, HEV infection remains underestimated, and Western countries are likely not immune to the virus. To date, two recombinant vaccines against hepatitis E, based on genotype 1, have been developed and approved in China, but further studies are needed to determine the duration of vaccination protection.
Ten-Year Results
This study is an extension of a randomized, double-blind, placebo-controlled phase 3 clinical trial of the Hecolin hepatitis E vaccine that was conducted in Dongtai County, Jiangsu, China. In the initial trial, healthy adults aged 16-65 years were recruited, stratified by age and sex, and randomly assigned in a 1:1 ratio to receive three doses of intramuscular hepatitis E vaccine or placebo at months 0, 1, and 6.
A hepatitis E surveillance system, including 205 clinical sentinels covering the entire study region, was established before the study began and maintained for 10 years after vaccination to identify individuals with suspected hepatitis. In addition, an external control cohort was formed to assess vaccine efficacy. The primary endpoint was the vaccine’s efficacy in preventing confirmed hepatitis E occurring at least 30 days after the administration of the third vaccine dose.
Follow-up occurred every 3 months. Participants with hepatitis symptoms for 3 days or more underwent alanine aminotransferase (ALT) concentration measurement. Patients with ALT concentrations ≥ 2.5 times the upper limit of normal were considered to have acute hepatitis. A diagnosis of HEV-confirmed infection was made for patients with acute hepatitis presenting with at least two of the following markers: Presence of HEV RNA, presence of positive anti-HEV immunoglobulin (Ig) M antibodies, and at least fourfold increase in anti-HEV IgG concentrations.
For the efficacy analysis, a Poisson regression model was used to estimate the relative risk and its 95% CI of incidence between groups. Incidence was reported as the number of patients with hepatitis E per 10,000 person-years.
Immunogenicity persistence was assessed by measuring anti-HEV IgG in participants. Serum samples were collected at months 0, 7, 13, 19, 31, 43, 55, 79, and 103 for Qingdao district participants and at months 0, 7, 19, 31, 43, 67, and 91 for Anfeng district participants.
Efficacy and Duration
The follow-up period extended from 2007 to 2017. In total, 97,356 participants completed the three-dose regimen and were included in the per-protocol population (48,693 in the vaccine group and 48,663 in the placebo group), and 178,236 residents from the study region participated in the external control cohort. During the study period, 90 cases of hepatitis E were identified, with 13 in the vaccine group (0.2 per 10,000 person-years) and 77 in the placebo group (1.4 per 10,000 person-years). This indicated a vaccine efficacy of 86.6% in the per-protocol analysis.
In the subgroups evaluated for immunogenicity persistence, among those who were initially seronegative and received three doses of hepatitis E vaccine, 254 out of 291 vaccinated participants (87.3%) in Qingdao after 8.5 years and 1270 (73.0%) out of 1740 vaccinated participants in Anfeng after 7.5 years maintained detectable antibody concentrations.
The identification of infections despite vaccination is notable, especially with eight cases occurring beyond the fourth year following the last dose. This information is crucial for understanding potential immunity decline over time and highlights the importance of exploring various vaccination strategies to optimize protection.
An ongoing phase 4 clinical trial in Bangladesh, exploring different administration schedules and target populations, could help optimize vaccination strategies. The remarkable efficacy (100%) observed over a 30-month period for the two-dose schedule (doses are administered 1 month apart) is promising.
The observation of higher IgG antibody avidity in participants with infections despite vaccination underscores the importance of robust antibody responses to mitigate disease severity and duration. Several study limitations, such as lack of data on deaths and emigrations, a single-center study design, predominance of genotype 4 infections, and the risk for bias in the external control cohort, should be acknowledged.
In conclusion, this study provides compelling evidence of sustained protection of the hepatitis E vaccine over a decade. The observed persistence of induced antibodies for at least 8.5 years supports the long-term efficacy of the vaccine. Diverse global trials, further investigation into the impact of natural infections on vaccine-induced antibodies, and confirmation of inter-genotypic protection are needed.
This story was translated from JIM, which is part of the Medscape professional network, using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication. A version of this article appeared on Medscape.com.