HCV vaccine could reduce transmission in people who inject drugs
A vaccine that would provide incomplete immunity against hepatitis C virus could still reduce the spread of the virus among drug users sharing syringes, according to study results published in Science Translational Medicine.
“Our data-driven mathematical modeling approach demonstrates that even with transient viral replication following exposure during injection drug use, if an effective vaccine were available, its use in drug user populations has the potential to reduce virus transmission and reduce new HCV infections in this population,” Marian Major, PhD, chief of the Laboratory of Hepatitis Viruses in the FDA’s Center for Biologics Evaluation and Research, told Infectious Disease News. “However, harm reduction programs should be maintained during implementation of any HCV vaccine in order to fully eliminate new infections among this population.”
According to Major and colleagues, factors that could affect HCV transmission through sharing syringes include the proportion of blood transmitted from used syringe based on syringe type, syringe rinsing, blood donors’ HCV RNA amount, the amount of drug and blood in the needle and syringe and infectious HCV RNA in blood.
Major and colleagues developed a mathematical model to calculate HCV transmission probabilities in injecting drug users as relative to HCV RNA titers. They used HCV cell culture virus to calculate for two types of syringes that would be fitted with two different types of needles that would hold a large or small amount of fluid after being injected.
They accounted for syringe type, rinsing and sharing frequency when estimating transmission risk between serodiscordant injecting drug users. Viral kinetics data of naive patients infected with HCV and reinfected patients who were cleared of an HCV infection were used.
Syringe sharing increased risk for HCV transmission by up to 10 times, with viral titers (log10 IU/mL) experiencing an approximately 25-fold increase, according to the researchers’ calculations.
“Cumulative analyses showed that, assuming sharing episodes every 7 days, the mean transmission risk over the first 6 months was greater than 90% between two people sharing syringes when one had HCV RNA titer greater than 5 log10 IU/mL,” the researchers wrote.
There was a decrease in cumulative risk between 1% and 25% for drug users with pre-existing immunity that rapidly controlled HCV. The risk decrease was dependent on HCV titer and syringe type.
“Science will dictate the timing of the availability of a safe and effective HCV vaccine,” Major said. “Development of effective vaccines for hepatitis C has been difficult for a variety of reasons, including challenges with developing a relevant animal model, viral diversity and determining the immune responses that correlate with immunity and protection. Because of these challenges, it will be some time before a safe and effective licensed vaccine will be available.” – by Bruce Thiel
Disclosures: The authors report no relevant financial disclosures.