** Shares in Sanofi SASY.PA drop around 3% as U.S. FDA appointed on Tuesday the agency critic Vinay Prasad as top vaccine official

** Prasad was appointed the director of the Center for Biologics Evaluation and Research (CBER), overseeing regulation of drugs, including vaccines

** Bernstein's analyst Florent Cespedes says Prasad's appointment put pharmaceutical stocks under pressure with vaccine companies being more impacted

** Shares in Sanofi, which is one of the world's largest vaccine makers by sales, trade at the bottom of France's blue-chip CAC 40 Index .FCHI

** They will see their worst day in almost a month, if losses hold

(Reporting by Michal Aleksandrowicz)

((michal.aleksandrowicz@tr.com))