Shares of Moderna, Inc. (MRNA) tumbled 6.44% in after-hours trading on Wednesday, following a series of concerning developments in the pharmaceutical regulatory landscape. The steep decline comes amid investor worries about potential changes in vaccine policies and regulatory scrutiny.

The primary catalyst for the sell-off appears to be the recent appointment of Dr. Vinay Prasad as the FDA's top vaccine regulator. Prasad, known for his critical stance on FDA policies and the U.S. Covid-19 response, replaces Dr. Peter Marks as director of the Center for Biologics Evaluation and Research. This change in leadership has sparked concerns about a potential shift in the FDA's approach to vaccine approvals and regulations, which could directly impact Moderna's business prospects.

Adding to the uncertainty, the FDA announced it will hold a meeting of experts on May 22 to discuss COVID-19 vaccine recommendations for the upcoming immunization campaign. This meeting, coupled with recent mass layoffs at the FDA as part of a major overhaul under Health Secretary Robert F. Kennedy Jr., has intensified worries about potential disruptions to the regulatory review of treatments and vaccines. The market reaction suggests investors are apprehensive about how these developments might affect Moderna's vaccine business and future approvals.