Some Individuals May Be Able to Develop Immunity to Hepatitis C, Study Says
Some people infected with hepatitis C are able to clear the virus from their bodies, suggesting that it is possible to develop a "potent immunity" to the disease, according to new research published in the April 27 issue of the Lancet, Newsday reports (Ricks, Newsday, 4/26). Researchers from Johns Hopkins University in Baltimore and the New York Academy of Sciences studied 164 Baltimore-area injection drug users who had never been infected with hepatitis C and 98 area injection drug users who had been previously, but were not currently, infected with the virus. Participants were tracked over four consecutive six-month periods and were considered infected with hepatitis C if their blood contained viral RNA. If viral RNA was not present in the blood at the next consecutive follow-up visit, the participant was considered free of the virus. Twenty-one percent of the participants who had never been infected with hepatitis C became infected during the study, while only 12% of those who were previously infected with the disease became re-infected. Among HIV-negative participants, individuals previously infected with hepatitis C were 12 times less likely to develop persistent hepatitis C infection. The study findings indicate that "immunity against viral persistence can be acquired and that vaccines should be tested to reduce the burden of HCV-related liver disease," the study authors state (Mehta et al., Lancet, 4/27). Dr. Stuart Ray, a professor of medicine at Johns Hopkins and a study co-author, said that a single hepatitis C vaccine based on one strain of the virus will probably not work because the virus has several mutated strains. However, he said that a vaccine might help prevent the liver damage that the virus causes (Newsday, 4/26).
Preventing Persistent Secondary Hepatitis Infection Difficult
The study results "warrant serious consideration by the wide community interested in a protective HCV vaccine," but preventing secondary persistent hepatitis infection in previously infected individuals will be a "challenge," Michael Grant of the Memorial University of Newfoundland's immunology program writes in an accompanying Lancet commentary. Although the study found that individuals previously infected with the virus are less likely to become re-infected than those never infected, the occurrence of secondary persistent hepatitis C infections in some members of the former group is "paradoxical" and "fit[s] poorly with the protective role attributed to adaptive immunity," Grant states. One explanation for persistent secondary infection is that the hepatitis C virus contains "sophisticated mechanisms to impede or evade immune responses." In addition, individuals who were previously able to clear the virus from their systems may have developed another illness, such as HIV, that could hamper immune response. "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 hepatitis C itself," Grant concludes (Grant, Lancet, 4/27).