Shares of gene therapy developers fall in premarket trading, after Vinay Prasad returns as top vaccine official at U.S. FDA a little more than a week after he left the agency

Capricor Therapeutics down 9.2% at $8.2; Shares of Sarepta Therapeutics SRPT.O down 7.3% at $16.9; Replimune Group Inc. down 5.7% at $5.

Prasad returns as the director Center for Biologics Evaluation and Research, which oversees costly and complicated biologic drugs, including vaccines and gene therapies at FDA

The news could be taken with "caution on how long, if at all, Prasad will actually be staying", Jefferies analysts say, adding that his reinstatement could impact vaccine makers and gene therapy developers "towards more evidence-based approach, which could be a double-edge sword in the near term"

A number of controversial decisions by the FDA regarding Sarepta's muscular disorder gene therapy, Elevidys, contributed to Prasad's departure late last month after a few months into the role