Efforts to make a hepatitis C vaccine started decades ago when the hepatitis C virus was first identified in 1989. Since then, researchers have studied several possible vaccines in animals. Some of these vaccines also have been tested in groups of people through research clinical trials.

But progress on creating a successful vaccine has been slow. In part, that's because the virus has many forms. The hepatitis C virus varies more than the hepatitis A and hepatitis B viruses. Hepatitis C has at least eight genetically distinct forms, called genotypes. Each of those genotypes also has many subtypes. To date, more than 100 subtypes of hepatitis C have been found.

The genetic diversity of hepatitis C means that different forms of the virus are found throughout the world. So to be effective everywhere, a vaccine needs to protect against all forms of the virus.

Another challenge in creating a hepatitis C vaccine involves the animals that are used for testing. In the past, chimpanzees were used in hepatitis C research because the way the virus infects them is similar to the infection in humans. But ethical concerns now significantly limit medical research involving these animals.

Effective treatment is available for hepatitis C. Medicines can get rid of the virus in most people who are diagnosed with it. But finding a vaccine still is very important. That's because hepatitis C typically doesn't cause symptoms until it's in its later stages, when it can lead to serious health concerns, such as cirrhosis and liver cancer. Researchers continue to work on developing an effective hepatitis C vaccine.