Research ArticleHepatitis C Virus

Modeling of patient virus titers suggests that availability of a vaccine could reduce hepatitis C virus transmission among injecting drug users

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Science Translational Medicine  11 Jul 2018:
Vol. 10, Issue 449, eaao4496
DOI: 10.1126/scitranslmed.aao4496

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Hampering hepatitis C virus transmission

No hepatitis C virus (HCV) vaccine is currently available, and evidence from studies in nonhuman primates suggests that any future human HCV vaccine would be unlikely to induce complete immunity against the virus. Major et al. examined whether lowered HCV titers potentially resulting from an imperfect vaccine might still stem HCV transmission in people who inject drugs. The authors measured the HCV RNA from infected human plasma retained in contaminated needles and syringes. Their mathematical model combining these measurements with published HCV viral kinetics data suggested that a partially effective vaccine could reduce the HCV transmission risk among individuals who share contaminated needles and syringes.

Abstract

The major route of hepatitis C virus (HCV) transmission in the United States is injection drug use. We hypothesized that if an HCV vaccine were available, vaccination could affect HCV transmission among people who inject drugs by reducing HCV titers after viral exposure without necessarily achieving sterilizing immunity. To investigate this possibility, we developed a mathematical model to determine transmission probabilities relative to the HCV RNA titers of needle/syringe-sharing donors. We simulated sharing of two types of syringes fitted with needles that retain either large or small amounts of fluid after expulsion. Using previously published viral kinetics data from both naïve subjects infected with HCV and reinfected individuals who had previously cleared an HCV infection, we estimated transmission risk between pairs of serodiscordant injecting drug users, accounting for syringe type, rinsing, and sharing frequency. We calculated that the risk of HCV transmission through syringe sharing increased ~10-fold as viral titers (log10 IU/ml) increased ~25-fold. Cumulative analyses showed that, assuming sharing episodes every 7 days, the mean transmission risk over the first 6 months was >90% between two people sharing syringes when one had an HCV RNA titer >5 log10 IU/ml. For those with preexisting immunity that rapidly controlled HCV, the cumulative risk decreased to 1 to 25% depending on HCV titer and syringe type. Our modeling approach demonstrates that, even with transient viral replication after exposure during injection drug use, HCV transmission among people sharing syringes could be reduced through vaccination if an HCV vaccine were available.

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