Why isn't there a hepatitis C vaccine?
Efforts to develop a hepatitis C vaccine started more than 25 years ago, when the hepatitis C virus was identified. Since then, researchers have studied more than 20 potential vaccines in animals. A few of these vaccines, developed mainly in the past decade, have undergone limited testing in people.
The following two clinical trials are now underway to find out if recently developed experimental vaccines are safe and effective in people.
- Therapeutic vaccine trial. The study population in this trial consists of people who already have chronic hepatitis C. The purpose of the trial is to determine whether each vaccine is safe and successful at reducing evidence of hepatitis C in participants' blood. Completion of this trial is expected in 2020.
- Prophylactic (preventive) vaccine trial. This trial involves people at high risk of becoming infected with hepatitis C. Its purpose is to determine the safety of the two vaccines and find out whether participants receiving either vaccine are less likely to become infected with the hepatitis C virus over a six-month period than are participants receiving a placebo (inactive) vaccine. This trial has already enrolled a large sample of participants. It ends in July 2018.
If these trials have good results, larger trials will still be necessary to verify this effect and determine the best way to deploy the vaccine.
Progress has been slow for a number of reasons, including:
Unique characteristics of the virus
The hepatitis C virus is more variable than are the viruses that cause hepatitis A and hepatitis B. For starters, hepatitis C virus occurs in at least six genetically distinct forms (genotypes) with multiple subtypes. About 50 subtypes have been identified.
Different hepatitis C virus genotypes (variants) cause most infections in different parts of the world. A global vaccine would have to protect against all these variants of the virus.
Limited animal models of hepatitis C infection
Hepatitis C virus can infect chimpanzees, and the infection in chimpanzees is similar to that in human adults. Ethical and cost concerns, however, limit medical research with these animals.