FDA panel backs Dynavax's hep B vaccine efficacy, not safety

Fri Nov 16, 2012 2:18am IST

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(Reuters) - A U.S. Food and Drug Administration panel voted unanimously to recommend the effectiveness of Dynavax Inc's hepatitis B vaccine Heplisav, but raised concerns about its safety, asking for more data from studies on a wider population.

The views of the panel of outside experts were based on data submitted by Dynavax that compared the safety and immunogenicity, or ability to evoke an immune response, of its Heplisav with that of an older vaccine named Engerix B by GlaxoSmithKline Plc.

"The immunogenicity data that was provided by (Dynavax) was excellent, but I have concerns with the population. I think what we have here is really really good but it is not representative of the United States," a panel member said.

Dynavax conducted the studies on 5,845 patients to support Heplisav's marketing approval application. The patients, mainly from the United States, Canada and Germany, were 18 years and older.

"Prior to the vote, (the panel members) peppered (Dynavax) with questions about the adverse events and the lack of sufficient representation of cross-sections of the populations in the study pool, specifically Asian-Americans, African-Americans and Hispanics," FDA spokeswoman Rita Chappelle said in an email.

The panel members asserted that Dynavax focus on a larger database of 10,000 or more ethnically diverse patients from a higher risk population that would highlight the benefits of the vaccine more prominently.

All 13 panel members favored the efficacy profile of Heplisav. Eight panel members questioned the safety of the vaccine based on available data, while five favored it. One panel member abstained from voting on the safety profile.

"I don't think the safety database is sufficiently large to support the recommendation for use (of the vaccine) in a general adult population, given that it contains an adjuvant," another member said.

Adjuvants are added to vaccines to improve their ability to trigger an immune response, but carry the risk of causing several potentially fatal adverse reactions.

"Products need to be both safe and effective for its intended use and in this case, the committee felt that Heplisav did not meet that threshold," FDA's Chappelle said.

In briefing-documents released on Tuesday, FDA staff had noted that while the incidence of autoimmune events in Heplisav-Engerix B studies were low, all autoimmune adverse events occurred in the Heplisav arm of the study.

The committee also stressed that Dynavax follow up on the health of hepatitis B patients who were enrolled in its studies.

The life-threatening viral disease attacks the liver and an estimated 800,000 to 1.4 million people in the United States are carriers of the chronic form of the infection, according to the Centers for Disease Control and Prevention. It contributes to an estimated 620,000 deaths worldwide each year.

The FDA will take the panel's opinions into consideration when it decides on whether to grant marketing approval to the vaccine on the scheduled date of February 24.

Dynavax's shares, which were halted at 0700 ET, had not resumed trading on the Nasdaq on Thursday well after the end of the panel meet at about 1438 ET.

The company's shares had gained about 20 percent on Tuesday after the FDA staff released briefing documents that pointed to no major safety concerns with the vaccine.

(Additional reporting by Vidya P L Nathan; Editing by Sriraj Kalluvila, Maju Samuel)

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