Merck's vaccine chief is stepping down, spurring widespread speculation that the departure could signal the start of a major management shake-up ahead of its merger with Schering-Plough.

Margaret McGlynn (photo [1]), once viewed as a CEO candidate, says she thought that this was a good time to pursue other "personal and professional aspirations." McGlynn, 49, has worked at Merck for 26 years and spent the last four years running the pharma giant's vaccine arm [2]. During that time Merck launched Gardasil, which has provided a major boost to the company's bottom line.

Analyst Tim Anderson wrote that the departure signals a looming upheaval in the ranks of Merck executives. "Our understanding is that over the coming weeks there could be a significant shake-up in the most senior ranks of the company, some of which could come as a surprise to investors."

- read the report [3] from the Wall Street Journal

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