In 1991, the Food and Drug Administration approved the first-ever treatment for the hepatitis C virus, or HCV. The results were dismal; very few people cleared the virus. Since then, researchers have developed increasingly more effective drugs with fewer side effects to treat hep C. Today, the latest treatment meds aren’t injected, they’re swallowed, and they can clear HCV from the blood within four to 12 weeks.

Once people suffering from hep C undergo these oral drug treatments and the virus is undetectable in their blood for six months after they’ve completed therapy, doctors say they’ve achieved a sustained virologic response (SVR) and they’re considered cured.

But some doctors warn that re-infection can occur after a patient achieves SVR if the person engages in high-risk activities, such as injecting drugs or getting a tattoo with a dirty needle. Also, recent study findings show that in some people, HCV can remain dormant in the body for a long time before waking up and causing a patient to relapse.

Says Theo Heller, MD, a researcher at the National Institutes of Health and one of the study’s authors, “We already know it can and does occur.”