Polio, diphtheria and measles – what do these diseases have in common? They are all caused by viruses that were virtually eradicated by vaccines. One University of New Mexico researcher is hoping to add another virus to that list: hepatitis C.
In a recently published study in the journal Science Translational Medicine, epidemiologist Kimberly Page, PhD, MPH, along with FDA scientist Marian Major and a team of researchers, showed that the development of a hepatitis C vaccine could significantly ease viral transmission among drug users.
When someone becomes infected with hepatitis C, the amount of virus circulating in the person’s bloodstream – referred to as viremia – explodes. “It is a slow, smoldering virus that causes liver inflammation," Page said. Over time, it can lead to high risk of liver damage and cancer.
It takes almost two months for the body to make antibodies against the virus. Even then, only some people’s immune systems can suppress the virus – and those who do often become re-infected.
The question is how – and why?
According to this study, needle sharing is a common reason, because residual blood that is left over in the needle from one drug user is often injected into the next user.
"There is some controversy,” Page said. “Are people getting infected from the residual blood? And, of course, the answer is yes, but not everyone. So, is it associated with having a lot of virus or a little bit of virus?"
That’s what the team wanted to find out. Using data on hepatitis C viral load in patients and viral retention in syringes from the lab, as well as global data on the natural history of the virus, the team created a mathematical model to simulate what viremia level would lead to diminished transmission risk from one drug user to the next during reinfection – and how vaccines would effect this risk.
"Usually, models look like kind of a steampunk picture,” Page said. “You've got one thing feeding into one part, and one thing feeding into another, and the assumption of death, and the assumption of new people coming into the population."
Feeding what they knew about hepatitis C transmission into this complex system, the researchers found that if there is only a small amount of blood in the syringe being shared with another user, the risk of reinfection drops substantially.
If drug users would simply rinse their syringes after use, Page explained, “We could reduce transmission simply because of there being less virus in the syringes that are the vector for transmission."
And this leads to one of Page’s goals – a hepatitis C vaccine that could be used in conjunction with existing therapies. A clinical trial for one version of a vaccine just wrapped up in New Mexico, and she’s hopeful.
"The vaccine is a T cell vaccine – it's meant to help people clear virus,” Page said. “It's meant to induce the immune response that we know is associated with spontaneous clearance."
Due to the high cost of current therapies to cure hepatitis C, a vaccine would aid in treatment, as well as preventing the virus from spreading to uninfected drug users, Page said.
"Our big take-home is if a vaccine induces low viremia – that mimics what we see with reinfection – we can reduce transmission,” she explained.
Page recognizes that the simulations data need to be confirmed in the field, but it doesn’t take away from the breadth and impact of this publication.
"I think that one of the strengths of this study is that the model used real data from the lab, from people, from so many sources,” she said. “It was brilliant. It's really cool, and I'm really pleased.”