Around 4 million people in the USA (and 170 million people worldwide) have been infected with hepatitis C virus (HCV). About 85% of people infected with HCV develop persistent infection and are at risk of long-term complications, including liver cirrhosis and liver cancer. Neither previous HCV infection nor vaccination protects against reinfection. However, HCV infection and vaccination in chimpanzees has been shown to reduce the magnitude and duration of symptoms after reinfection. David Thomas and colleagues from Johns Hopkins School of Medicine, Baltimore, USA, aimed to establish whether similar immunity could be achieved in man.
From a study of injecting-drug users, the investigators identified 164 people who had no evidence of previous HCV infection and 98 individuals who had been previously (but were not currently) infected with HCV. The incidence and persistence of HCV infection in these two groups was compared over four consecutive 6-month periods.
The incidence of HCV infection was halved for people who had been previously infected, compared with those who had not been previously infected (12% compared with 21%, respectively). Among HIV-1-negative people, those previously infected were 12 times less likely than people infected for the first time to develop persistent infection.
David Thomas comments: “The high rate of HCV infection in injecting-drug users underscores the importance of preventing HCV infection. Since it appears that immunity can be acquired to protect against viral persistence, vaccines should be tested to reduce the medical consequences of HCV infection among people at highest risk.”
In an accompanying Commentary (p 1452), David Grant from Memorial University of Newfoundland, Canada, concludes: “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.”
Contact: Dr David L Thomas, 424 North Bond Street, Johns Hopkins School of Medicine, Baltimore, Maryland 21231, USA; T) +1 410 955 0349; F) +1 410 614 7564; E) dthomas@jhmi.edu
Dr Michael Grant, Immunology Program, Division of Basic Medical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St John’s, NF A1B 3V6, Canada; E) mgrant@mun.ca
Journal
The Lancet