The drugmaker’s partner, Dynavax Technologies, says the agency placed a clinical hold on two Investigational New Drug applications for Heplisav, an investigational hepatitis B vaccine being jointly developed for use in adults. A clinical hold is an order issued by the FDA to a drugmaker to delay a proposed clinical trial or suspend an ongoing trial, the companies note in their statement.

The FDA placed the clinical hold on the vaccine because of a serious adverse event that occurred in one subject who received Heplisav in a Phase III trial conducted outside the US. The subject was preliminarily diagnosed with Wegener’s granulomatosis, an uncommon disease in which blood vessels are inflamed. All subjects in the have received all doses per the protocol and will continue to be monitored.

Administration of the vaccine has been suspended in the only Heplisav study in which injections were given actively, a fully enrolled Phase II study in end stage renal disease subjects in Canada. About 2,500 people have been vaccinated with more than 5,000 doses of the vaccine in 10 clinical trials spanning seven years, the companies disclosed, while maintaining there were no reports of Wegener’s granulomatosis in these trials.

No additional clinical trials with Heplisav will be initiated until the clinical hold has been resolved. The medical history of the person who experienced the serious adverse event is being scrutinized in hopes of determining whether the disease was a pre-existing condition or related to the vaccine.