Trial Evaluating Experimental Hepatitis C Vaccine Concludes

May 29, 2019

An experimental vaccine was not found to be effective at preventing chronic hepatitis C virus (HCV) infection in adults, according to results from a clinical trial sponsored by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

The trial began in March 2012 at sites in California and Maryland; a site in New Mexico was added in September 2015. The Phase 1/2 clinical trial was evaluating whether the experimental prime-boost vaccine known as AdCh3NSmut1/MVA-NSmut was safe and could prevent chronic HCV infection—defined as persistent presence of HCV in the blood for six months after initial detection of infection.

The trial enrolled 548 participants ages 18 to 45 years with a recent history of injecting drugs. The participants were randomly assigned to receive the experimental vaccine (a dose of AdCh3NSmut1 followed by a dose of MVA-NSmut 56 days later) or two placebo doses 56 days apart. Investigators report that 14 of the 275 participants in the experimental vaccine group and 14 of the 273 participants in the placebo group became chronically infected with HCV. The results indicate that the candidate vaccine failed to offer increased protection against chronic HCV infection compared to placebo. No vaccine-related serious adverse events were reported. Seven participant deaths were reported during the clinical trial that were deemed not related to the experimental vaccine. Additional analyses of the trial data are ongoing.

If untreated, HCV infection can lead to chronic liver disease. People who inject drugs are at an increased risk for HCV infection because the virus can be transmitted by sharing needles, syringes, or other equipment to prepare or inject drugs. Antiviral drugs can now cure more than 95% of all treated patients with HCV infection. However, no vaccine exists currently to prevent HCV infection. Many people are unaware that they are infected and continue to unknowingly spread the virus. People who have been cured also can be re-infected if exposed again. An HCV vaccine would be an important public health tool to interrupt and control HCV spread and to protect high-risk populations, such as people who inject drugs.

NIAID continues to support HCV research and is hosting an HCV vaccine workshop on May 29, 2019, in Rockville, Maryland. At the meeting, NIAID scientific experts and outside collaborators will discuss plans for future HCV vaccine designs.

Additional details about the trial are available on under identifier NCT01436357. The trial concluded in May 2018, and results will be published on in the coming weeks. The trial was conducted through an NIAID contract (HHSN266200400074C) to the University of California, San Francisco, part of the NIAID-funded Sexually Transmitted Infections Clinical Trials Group. The Switzerland-based company Okairos, which was acquired by GSK in May 2013, provided the prime-boost vaccine for the trial.

NIAID conducts and supports research—at NIH, throughout the United States, and worldwide—to study the causes of infectious and immune-mediated diseases, and to develop better means of preventing, diagnosing and treating these illnesses. News releases, fact sheets and other NIAID-related materials are available on the NIAID website.

About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit


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