Up until about ten years ago an effective vaccine for hepatitis C was seen as a distant prospect. However, advances in the understanding of the disease and in vaccine development have made the chances of a workable vaccine more feasible, if still some way off.
Two features of HCV infections have encouraged researchers into thinking that a vaccine might be possible. A significant number of people infected with HCV do not develop chronic hepatitis which means the immune system is capable of clearing the virus and there is also now evidence that some people have a natural immunity to HCV. If these methods of viral clearance and natural protection against HCV can be properly understood and harnessed then there is the chance of developing an effective vaccine.
Over recent years there have been significant developments in ways of making and delivering vaccinations. This has led to the possibility of designing vaccines to treat people who already have hepatitis C (therapeutic vaccines) as well as protecting uninfected people (prophylactic vaccines).
a. Therapeutic Vaccines
In theory vaccines could be targeted at different stages of the diseases. One vaccine could prevent people who had recently been infected from developing a chronic infection; another vaccine could be targeted to limiting scarring and inflammation of the liver in people with chronic hepatitis C. However, this is a new and evolving area of research and to date only one viral infection (a type of herpes) has been successfully treated in this way. In one trial a therapeutic vaccine appeared to prevent scarring and inflammation of the liver from progressing in most patients.
b. Preventative (prophylactic) Vaccines
Developing a traditional preventive vaccine based on an antibody response (which prevents viruses from reaching their targeted cells) has been extremely difficult because of HCVs tendency to mutate frequently.
An effective vaccine would have to stimulate T cells (vital HCV killing immune cells), as well as antibody producing B cells. In a recent vaccine trial on chimpanzees there was the first evidence that a vaccine against all strains of the virus might be possible. The chimpanzees that had cleared an infection with one genotype show protective immunity to multiple genotypes.
