Doing the maths to cut Hepatitis C in injecting drug users

The sharp end of the needle. Hitthatswitch

Hepatitis C is a blood borne virus and a major cause of liver disease and liver cancer. Around 150m people globally are estimated to suffer from the virus and in the UK, and many developed countries, people who inject drugs are at the biggest risk.

Of the 150,000 people with chronic hepatitis C in the UK, over 85% are current or former intravenous drug users. And about 40% of people who inject drugs are chronically infected with Hep C, compared to only 1% infected with HIV.

To prevent Hep C and its related liver disease, it’s clear we need to manage and prevent the disease among people who inject drugs.

Traditional harm reduction interventions

Currently, programmes to prevent Hep C transmission among people who inject drugs generally centre on needle and syringe schemes, which increases use of sterile equipment and lowers the risk of needle sharing, and opiate substitution treatment, which can reduce how often someone injects.

In the UK there has been considerable investment in both harm reduction measures – and it’s estimated that about half of injecting drug users may be on one intervention or the other. And evidence on the effectiveness of these strategies suggest that either can reduce Hep C transmission by about 50%, but combining them could reduce Hep C risk by 80%.

Our previous modelling work suggests that scaling up traditional harm reduction interventions can reduce the Hep C burden among people who inject drugs. For example, if current harm reduction measures] were removed, then over 80% of these drug users could have been chronically infected with Hep C, instead of the 40% seen today.

However, chronic Hep C in the UK remains high – and recent trends have not fallen - so it’s clear that we need to urgently find a new way of tackling the problem.

Hep C treatment as prevention

Effective treatments to cure Hep C do exist and are effective in about 60% of cases. These could also be used for prevention. Our model projections show that scaling up antiviral treatment for Hep C could reduce transmission. In some circumstances treating people who inject drugs would be more cost-effective than treating non or ex-drug users.

Making a maximum impact

In a recent study published in Clinical Infectious Diseases, we also assessed the potential impact of combining Hep C interventions - traditional harm reduction programmes (opiate substitution therapy, needle and syringe programmes) and antiviral treatment. Our projections suggest that rapid and substantial reduction in Hep C prevalence among people who inject drugs isn’t possible using traditional harm reduction measures alone, but is feasible when combined with antiviral treatment.

In general, we found that increasing coverage of traditional harm reduction programmes by 20% reduces the number of antiviral treatments required to achieve a given aim by about 30%. To halve the prevalence of chronic Hep C within ten years in a population where it is currently 40%, for example, would require treating 38 injecting drug users per 1000 each year. But if coverage of preventative measures were increased by 40%, to achieve the same reduction would require 23 users to be treated per 1000.

It’s expensive to cure Hep C

Current Hep C drugs cost about US$15,000 (£9,700) per treatment course. Newer Hep C drugs could increase cure rates over 90% but will be incredibly expensive - likely to be more than US$50,000 (£32,000) per treatment course. Few intravenous drug users are treated with antivirals. Some doctors are reluctant because they’re concerned that the drug users they treat won’t stick to antivirals, or because of the possibility of reinfection through further intravenous drug use.

In contrast the cost of delivering opiate substitution treatment has been estimated at about $10–$15 per day (£7-£10) and high-coverage needle and syringe programmes can cost $500 (£325) per year.

Strategies that increase prevention to minimise the number of antiviral Hep C treatments is likely to be seen as a more efficient use of resources. And especially as they bring other benefits including reducing the risk of HIV and bacterial infections. Opiate substitution treatment in particular reduces drug-related deaths and crime and promotes a better quality of life.

Limiting factors

Our work supports current European recommendations on Hep C prevention and a combined approach for maximum impact.

But there is a limit to the math. Our model projections explain the why but not the how: empirical evidence on how best to scale-up antiviral treatment, target injecting drug users who are future Hep C transmitters, and combine Hep C treatment with other interventions. Or indeed, how best to manage the cost of expensive antivirals and how they could best be used.

It might be that affordability prevents more use of antivirals. But we’re some way further to understanding why combining interventions might prove more effective in tackling the Hep C epidemic in the long run.