First report of acquired HCV immunity lifts vaccine hopes

A report in the Lancet suggests that some people can acquire immunity against chronic hepatitis C virus (HCV) infection, echoing earlier findings in chimpanzees. Despite the ‘alarming’ rate of infection within the study cohort, the authors say their discovery could help in the search for an effective HCV vaccine.

HCV is a major cause of acute hepatitis and chronic liver disease, including cirrhosis and liver cancer. Globally, an estimated 170 million people are chronically infected with HCV, and 3–4 million people are newly infected each year. HCV is spread primarily by direct contact with human blood, and is therefore common among those who share needles without adequate sterilisation.

From a local community of intravenous drug users, Shruti Mehta and fellow epidemiologists at Johns Hopkins School of Public Health used blood tests to identify 164 people who had never been infected with HCV and 98 who had been infected but had cleared the infection.

Of participants who had not been infected previously, 21% became infected with HCV during the two-year study period. In contrast, 12% of participants who had already cleared an HCV infection in the past became infected again.

“Those who previously recovered from infection and were then infected again often resolved the new infection, suggesting that immunity could be developed that promotes recovery,” said David Thomas, co-author. “This is important because prior studies that showed that you could be reinfected cast doubt on the prospects of developing an effective vaccine.”

Although re-infection did occur in the study, these infections usually cleared and would not be expected to cause disease, claim the researchers.

Furthermore, co-infection with HIV had a significant impact on the likelihood of becoming infected with HCV, the report indicates. People who were not infected with HIV were 12 times less likely to develop chronic HCV infection than those who were HIV positive.

In a related editorial, David Grant (Memorial University, Canada) comments: ‘While the most positive interpretation of this unique study offers hope that protection against HCV can be acquired, the immunogenicity of human vaccines still pales compared with that of genuine infections. The need for continued creative research in vaccine design is emphatically underlined by the, at best, part protection against persistent secondary infection conferred by clearance of primary infection with HCV itself.’