A recent phase III trial conducted in China revealed that a three-dose vaccine regimen known as HEV239 has shown high efficacy in preventing hepatitis E virus (HEV) infections over a 10-year period. The study, led by Shoujie Huang, MSc, from Jiangsu Provincial Centre for Disease Control and Prevention, reported an efficacy rate of 83.1% in the modified intention-to-treat analysis and 86.6% in the per protocol analysis among adults aged 16 to 65 years. The results showed that vaccinated individuals had significantly fewer cases of HEV infection compared to those who received a placebo, with milder symptoms and reduced alanine aminotransferase elevation.
HEV is a major cause of acute viral hepatitis worldwide, leading to approximately 20 million infections and 70,000 deaths annually. The virus is predominantly found in regions such as Africa, Central America, and Asia, with increasing reports of transfusion-related cases in Europe. In the United States, the prevalence of HEV infection remains unclear due to limited surveillance and commercially available testing options. However, studies have indicated a seroprevalence of HEV antibodies among blood donors, suggesting past and recent infections.
HEV is categorized into different genotypes, with HEV-1 and HEV-2 transmitted through contaminated water and specific to humans. On the other hand, HEV-3 and HEV-4 are zoonotically transmitted and often linked to the consumption of undercooked meat from animals like boar, deer, and pig. The majority of individuals in the study were found to have HEV-4, highlighting the zoonotic nature of the infection and the potential for cross-species transmission.
The study also examined the persistence of HEV antibodies in vaccinated individuals, showing high levels of detectable antibodies over several years. In one Chinese township, 87.3% of vaccine recipients maintained antibodies at 8.5 years, while 73% in another township still had detectable antibodies at 7.5 years. This long-term immunity has been crucial in providing protection against HEV infections, raising questions about the efficacy during large outbreaks with higher exposure rates.
While the World Health Organization has endorsed the HEV239 vaccine for outbreak response since 2015, the level of protective antibodies required for immunity against HEV remains uncertain. Safety data from previous studies indicated no serious adverse effects related to the vaccine, but concerns remain regarding its effectiveness in vulnerable populations such as pregnant women and immunocompromised patients. Continuous monitoring and research are essential to evaluate the long-term benefits and potential risks associated with the hepatitis E vaccine.