If this fibrosis progresses far enough, it results in complete blockage, cirrhosis, a serious condition which may induce fatal liver failure, and which often induces primary liver cancer. About 20% of patients develop cirrhosis within 20 years of infection. Until then, few experience any symptoms at all. In all this time, individuals are fully infectious.
Luckily, hepatitis C is a very difficult virus to transmit. Direct blood contact is the only known path of direct transmission. Sexual transmission does not seem likely, although the possibility is still being investigated. Married partners of infected individuals rarely get the virus, and its incidence among promiscuous gay men is no higher than among the population at large.
Why not move vigorously to produce a vaccine directed against hepatitis C? This turns out to be particularly difficult for this virus. Infected individuals produce antibodies directed against the virus, but the antibodies don't protect them. Hepatitis C virus evades our antibody defenses by high mutation rates, just as the AIDS virus does. By the time antibodies are being produced against one version of the virus, some of the viruses have already mutated to a different form that the antibody does not recognize. Like chasing a burglar who is constantly changing his disguise, the antibodies never learn to recognize the newest version of the virus.
Attempts to find a hepatitis C vaccine are instead focused on the part of our immune system that attacks infected liver cells. Unlike the ineffective antibody defense, our bodies' cytotoxic T cells clearly are able to detect and attack cells carrying hepatitis C proteins. A vaccine that stimulates these cytotoxic T cells might enable them to eliminate all infected cells at the start of an infection, stopping the disease in its tracks before it got started. A serious effort is being made to develop such a vaccine.
It doesn't look like an effective vaccine is going to be available anytime soon. In the meantime, public concern is beginning to be felt in Washington. The NIH has increased funding for hepatitis C research to $33.6 million for next year. However, this is a paltry amount compared to the $1.8 billion to be spent on AIDS virus research. As the death rates from hepatitis C exceed those for AIDS in the next few years, we can hope NIH will further intensify its efforts.