Direct-acting antivirals can now cure every kind of hep C, quickly. The debilitating ordeal associated with the former treatment, interferon, is long gone. But for some patients, DAA treatment has a big-with a capital B—drawback.

The Federal Drug Administration has just ruled that a warning for people with hepatitis B must be included in packages of many direct-acting antivirals. The ruling came after the agency found 24 inactive cases of hepatitis B had become virulent among patients being treated for the C disease.

Unlike hep C, no cure exists for chronic hepatitis B. However, a vaccine can protect against it, and treatment can suppress replication of the virus.  But uncontrolled hepatitis B can cause liver failure.

The FDA warning on the hep C antivirals states that people infected with HBV risk reactivation of hepatitis B.