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A three-dose vaccine regimen prevented hepatitis E virus (HEV) infections with high efficacy in adults over the course of 10 years, a phase III trial from China found.

The HEV239 vaccine, sold under the name Hecolin outside the U.S., had an efficacy rate of 83.1% (95% CI 69.4-91.4) in the study's modified intention-to-treat analysis and 86.6% (95% CI 73.0-94.1) in a per protocol analysis over that period, reported researchers led by Shoujie Huang, MSc, of Jiangsu Provincial Centre for Disease Control and Prevention in Nanjing, China, in .

Among the 112,604 participants ages 16 to 65 years randomized to receive three intramuscular doses of the vaccine or placebo, just 13 cases of HEV infection were diagnosed among vaccinated individuals compared with 77 in the placebo group (0.2 vs 1.4 cases per 10,000 person-years).

Cases that did occur were less severe in the vaccinated group by alanine aminotransferase elevation measures and duration of symptoms.

"This study is the first to unveil the remarkable efficacy of the hepatitis E vaccine over a decade-long span, offering substantial evidence of its protective efficacies," the authors wrote.

HEV is a leading cause of acute viral hepatitis worldwide, resulting in an . HEV primarily occurs in Africa, Central America, and Asia. Transfusion-related HEV is increasingly reported in Europe, and many large outbreaks occur in refugee camps.

, in part because of a lack of surveillance or an FDA-approved, commercially available HEV assay. However, an analysis of showed approximately 10% seropositivity for HEV immunoglobulin G (IgG), reflecting past infection, and 0.58% for HEV IgM, indicating recent infection. Active HEV viral RNA was detected in one of 9,500 donors.

In an , Florence Abravanel, PhD, of Universite Toulouse in France, and Sebastien Lhomme, PharmD, PhD, of the National Reference Centre for Hepatitis E in Toulouse, pointed out that among new wildlife-origin viruses for risk of animal-to-human spillover.

Genotypes HEV-1 and HEV-2 are transmitted via contaminated water and are specific to humans. However, HEV-3 and HEV-4 are zoonotically transmitted, often by eating uncooked or undercooked meat and offal of boar, deer, and pig. Most of the people in the study had HEV-4, the study authors noted.

Huang and colleagues also looked at the persistence of HEV IgG and IgM antibodies over time in the vaccine recipients. Of 291 vaccine recipients in the Chinese township of Qindong, 87.3% maintained detectable antibody concentrations at 8.5 years. Among 1,740 vaccinated in the Anfeng township, 73% had detectable antibodies after 7.5 years.

While Abravanel and Lhomme also called the long-term efficacy "remarkable," they noted that the number of symptomatic HEV cases was relatively small in the study cohorts for such a long period of time, suggesting low levels of HEV exposure in the geographic areas studied. "In the case of large outbreaks, would this efficacy be so impressive?" they questioned. The World Health Organization has the HEV239 vaccine for outbreak response since 2015, and the first such use occurred in South Sudan in 2022.

Moreover, despite the study authors reporting the persistence of HEV antibodies over time, the level of HEV IgG that is protective against HEV infection remains unknown, Abravanel and Lhomme pointed out.

Safety data of the vaccine were reported , showing no serious adverse effects attributed to the vaccine. "The evidence of safety and effectiveness in vulnerable populations, such as pregnant women and patients who are immunosuppressed, is still scarce," Abravanel and Lhomme pointed out.

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