A long-term study of a hepatitis E virus (HEV) vaccine showed that it is 86.8% effective and that immunity can last for up to 4.5 years.
In a blinded, placebo-controlled, phase 3 trial, Jun Zhang et al randomly assigned 112,604 healthy adults in Dongtai (in the Jiangsu province of China) to receive either 3 doses of a hepatitis E vaccine (Hecolin Xiamen Innovax Biotech, n=56,302) or hepatitis B vaccine (controls, n=56,302).
In the March 5 issue of the New England Journal of Medicine, they report that during the 54 month follow-up period, they identified 7 cases of hepatitis E in the vaccine group (0.3 cases per 10,000 person-years) and 53 cases in the control group (2.1 cases per 10,000 person-years). The vaccine efficacy was 86.8% (95% confidence interval, 71 to 94) in the modified intention-to-treat analysis.
Of the participants who were assessed for immunogenicity and were seronegative at baseline, 87% of those who received 3 doses of the hepatitis E vaccine maintained antibodies against HEV for at least 4.5 years; HEV antibody titers developed in 9% in the control group. The rate of adverse events was similar between groups.
Medscape Medical News explained that patients were followed through a hepatitis surveillance program covering 205 village and private clinics, as well as township and city hospitals throughout Dongtai. Hepatitis was confirmed before unblinding based on detection of immunoglobulin (Ig)M against HEV, HEV RNA, and/or a level of IgG against HEV that was at least 4-fold as high as a level measured previously at any time during the same illness.
In addition to efficacy, the study authors evaluated immunogenicity of the vaccine and found that 52% of the 5567 participants tested were seronegative at baseline; of these, 99.9% seroconverted after receiving the HEV vaccine. Rates of seroconversion were similar among participants who received 1, 2, or 3 doses of the HEV vaccine and who were seronegative at baseline.
The New England Journal of Medicine article explains that HEV infection, a common worldwide cause of hepatitis, can either be spread by waterborne infection (HEV genotypes 1 or 2, mainly in resource-limited countries) or between animals and humans (HEV genotypes 3 or 4, in resource-limited and developed countries).
Zhang et al. acknowledge limitations to the study, such as fluctuations in the sensitivity for disease surveillance and the fact that most cases of hepatitis were caused by HEV genotype 4.
Kenneth E. Sherman (director of the Division of Digestive Diseases at the University of Cincinnati College of Medicine) told Medscape Medical News that the genotype of HEV present in China, where the study was performed, is not the dominant type present in Europe and the US (genotype 3). Further studies are therefore needed to determine whether this vaccine will be effective against other genotypes.
However, Sherman added that “an efficacious and durable vaccine for HEV is an important step in preventing HEV disease in endemic areas of the world and perhaps to travelers to those areas”.
The vaccine has not yet been approved by the US Food and Drug Administration.