Efforts to develop a hepatitis C vaccine started more than 30 years ago, when the hepatitis C virus was identified. Since then, researchers have studied several potential vaccines in animals. Some of these vaccines, developed mainly in the past decade, have undergone limited testing in people.

One ongoing clinical trial includes:

• A therapeutic vaccine trial. Researchers are testing a vaccine therapy on people who already have chronic hepatitis C. The purpose is to determine if the vaccine can help the body build an immune response and thereby treat the hepatitis C infection. It will also determine if the vaccine is safe and able to protect against future infection.

  If this trial has good results, larger trials will be necessary to verify this effect and determine the best way to deploy the vaccine.

Progress on developing a successful vaccine has been slow for a number of reasons, including:

The unique characteristics of the virus

The hepatitis C virus is more variable than hepatitis A and hepatitis B viruses. Hepatitis C occurs in at least seven genetically distinct forms (genotypes) with multiple subtypes. About 60 subtypes have been identified.

Different genotypes cause infections in different parts of the world. A global vaccine would have to protect against all variants of the virus.

Limited animal models of hepatitis C infection

A hepatitis C infection in chimpanzees is similar to an infection in humans. However, ethical and cost concerns limit medical research with these animals.

Although researchers are still working to develop an effective vaccine, new medications can cure nearly everyone who is infected with hepatitis C.