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What happened

Dynavax Technologies Corp.'s (NASDAQ:DVAX) SEC filing yesterday suggests that a FDA decision on the company's hepatitis B vaccine is on track; however, worries that the FDA will reject the vaccine in December sent shares tumbling 13% today.  

So what?

Earlier this year, the FDA delayed a decision on the company's Heplisav-B vaccine to December from November, and last month, the FDA canceled a key advisory committee meeting to discuss the vaccine, saying it needed more time.

Yesterday, Dynavax said it has received "anticipated requests for information from the U.S. Food and Drug Administration's review team" and that "the review team's questions are in line with the company's expectations."

The company also indicated that it's working quickly in hopes of avoiding another delay to the FDA's decision date for Heplisav-B, which is currently December 15.

However, industry watchers, including's Adam Feuerstein, aren't convinced that a decision in December will go Dynavax's way. Feuerstein wrote today that over the past 10 years, 13 of 15 cancelled advisory committee meetings preceded an FDA rejection -- a track record that doesn't seem to bode well for Dynavax.

Now what?

Engerix-B, the leading hepatitis B vaccine today, requires three separate doses over a six-month period, and because of that schedule, many patients fail to get all of their shots and, thus, are inadequately protected against the virus.

Dynavax's Heplisav-B is dosed just twice over one month, so an approval could dramatically improve patient adherence. However, the FDA will need to determine that Heplisav-B is safe prior to approving it, and that matter may still be up for debate. Regulators rejected Heplisav-B in 2013 because of the risks of autoimmune diseases, and while Dynavax has completed studies addressing the risk of autoimmune disease, the FDA's recent behavior suggests it might not yet be convinced of Heplisav-B's safety.

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