The US Food and Drug Administration (FDA) has placed a clinical hold on the two Investigational New Drug (IND) applications for Heplisav, an investigational hepatitis B vaccine for use in adults being jointly developed by Dynavax Technologies Corporation and Merck & Co., Inc. A clinical hold is an order issued by FDA to the sponsor to delay a proposed clinical trial or suspend an ongoing clinical trial.

The FDA has placed the clinical hold on the investigational vaccine because of a serious adverse event (SAE) that occurred in one subject who received Heplisav in a phase III study being conducted outside the United States. The subject was preliminarily diagnosed as having Wegener's granulomatosis, an uncommon disease in which the blood vessels are inflamed. All subjects in this phase III study have received all doses per the study protocol and all will continue to be monitored. Administration of vaccine has been suspended in the only study of Heplisav in which injections were being administered actively, a fully enrolled phase II study in End Stage Renal Disease subjects being conducted in Canada. A total of approximately 2,500 individuals have been vaccinated with more than 5,000 doses of Heplisav in 10 clinical trials spanning approximately seven years. There were no prior reports of Wegener's granulomatosis in these trials.

No additional clinical trials with Heplisav will be initiated until the clinical hold has been resolved. Dynavax and Merck, along with additional collaborators, including clinical investigators and leading experts, are evaluating the medical history of the individual who experienced the SAE to understand better the timing and onset of the disease symptoms, including whether it was a pre-existing condition or was related to vaccine administration.