Why Is There No Vaccine For Hepatitis C?

3 Barriers to Creating an Effective Preventive Vaccine

doctor prepping a vaccine
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Vaccines have long seen as the key to ending epidemics that have threatened the public's health, including polio, measles, rubella, and diphtheria.

A similar effect has been seen with the hepatitis A vaccine, introduced in 1995, and the hepatitis B vaccine, first introduced in 1981. With the implementation of a national vaccination strategy, the number of hepatitis A and B infections in the United States has declined by more than 95 percent and 90 percent, respectively.

This, naturally, places the spotlight on hepatitis C and questions why we have yet to develop a vaccine able to prevent what is arguably the most serious of the three major hepatitis types?

The Scale of a Hepatitis C Epidemic

The scale of the problem is astonishing. According to a review from the World Health Organization, over 70 million people are chronically infected with the hepatitis C virus (HCV), including over three million Americans. Of these, nearly 400,000 die of the disease each year, mainly as a result of cirrhosis and liver cancer.

Moreover, of the more than 1.5 million new infections that occur annually, anywhere from 70 percent to 85 percent will go on to develop a chronic infection of which 70 percent will eventually develop a liver disease.

To put these numbers into perspective, the rate of new HCV infections outpaces that of HIV, while the number of people chronically infected with hepatitis C is more than double that of HIV (33 million).

Challenges in Developing a Vaccine

While there are today treatments able to cure many people living with HCV, the only obvious way to end the epidemic is with an affordable and safe preventative vaccine. To date, scientists have been stymied in their efforts to find one.

While many believe that a hepatitis C vaccine is attainable (even more so, perhaps, than an HIV vaccine), there are a number of key barriers to overcome.

Among them:

  1. HCV has multiple strains against which a single vaccine may not work. All told, there are seven major HCV genotypes, each of which have different conformations and characteristics. Vaccine design is dependent on these characteristics to establish, among other things, where a vaccine molecule is meant to attach to a virus in order to neutralize it. Think of it as key. With each conformation, the location of the key—and the way in which the key works—varies enormously. As such, while stopping one viral strain is possible, it may only enable another to take its place.
  2. HCV mutates constantly and erratically. As a virus, HCV is prone to genetic coding mistakes as it rapidly makes copies of itself. What this means is that, even among a single genotype, there are innumerable subtypes and an enormous diversity in the viral population. Because of this, even if a vaccine were able to prevent a single HCV genotype, there would likely be subtypes resistant to the vaccine. If so, the minor subtype would be able to replicate unchecked and, as such, evade the effects of the vaccine.
  3. There is a lack of animal models in which to perform research. With HIV, for example, scientists are able to perform animal studies because there is a similar virus called the simian immunodeficiency virus (SIV) found in primates. There is no such non-human HCV equivalent in nature. To date, scientists have only found HCV-like viruses in horses, rodents, and bats, which are, at best, distant relatives. With that being said, some research teams have developed systems by which to culture the virus and gain greater, real-time insight into how the virus infects host cells and how to prevent that from happening.

    Frontiers in Research

    Despite these considerable barriers, scientists are moving ever closer to identifying a vaccine model able to prevent HCV infection. While many believe that a single vaccine is unlikely to treat all major genotypes, most seem confident that the same principles governing one vaccine should be able to be "tweaked" to create others

    There are a number promising candidates under investigation. Among them, researchers in Australia are investigating a vaccine that was initially designed to treat rather than prevent HCV infection. The vaccine, which has already been shown to be safe in humans, is undergoing a large-scale trial among prison populations in New South Wales, a community in which HCV rates are inherently high.

    Meanwhile, other scientists are striving to map the genetic sequence of the HCV-like virus in horses, which is the closest cousin to the type seen in humans. Many believe that if scientists are able to deactivate or neutralize that virus, the same principles can be applied to the human type, opening the door to an effective vaccine in anywhere from five to ten years.

    Sources:

    Abdelwahab, K., and Said, A. "Status of Hepatitis C Virus Vaccination: Recent Update." World J Gastroenterol. 2016. 22(2):862-73. DOI: 10.3748/wjg.v22.i2.862.

    Centers for Disease Control and Prevention. "Viral Hepatitis: Hepatitis C Information." Atlanta, Georgia; updated October 17, 2016.

    World Health Organization. "Hepatitis C: Fact Sheet." Geneva, Switzerland; updated October 17.