Merck, Dynavax announce positive Heplisav results

After 48 weeks of therapy, three out of every four patients receiving boceprevir in combination with standard therapy had undetectable levels of the virus. That compares to 38 percent with undetectable viral levels in the standard therapy arm.

Schering-Plough data pushed down the share value of rival Vertex Pharmaceuticals.

In the study, 95.1 percent of subjects who received Heplisav developed protective antibodies to hepatitis B versus 81.1 percent of subjects who received Engerix-B, a marketed drug.

Back in April the FDA put a clinical hold on the drug's development because one subject was suspected to have Wegener's granulomatosis, an rare inflammation of blood vessels. The hold is still in effect.