Merck & Co's vaccines chief, Margie McGlynn, who oversaw the launch of its Gardasil cervical cancer vaccine among other products, will step down on November 1, a company spokeswoman said on Monday.

Merck announced the resignation of McGlynn, 49, internally on Friday, spokeswoman Amy Rose said. No replacement has yet been named.

Vaccines have become an increasingly important part of the drugmaker's business. Aside from Gardasil, McGlynn oversaw the launch of the Rotateq rotavirus vaccine and Zostavax shingles vaccine.

McGlynn, who has worked at Merck for 26 years, previously helped run U.S. commercial operations and had been thought of by Merck watchers as a possible CEO candidate.

She has professional and personal aspirations she'd like to pursue, Rose said, when asked about the reasons for McGlynn's departure.

Although Gardasil has become a blockbuster product, its sales have been more sluggish in the face of competition from a rival vaccine made by GlaxoSmithKline.

Tim Anderson, an analyst at Sanford Bernstein, said McGlynn's departure was likely just the beginning of changes at Merck, which is expected to complete its $41 billion acquisition of Schering-Plough by the end of the year.

Our understanding is that over the next coming weeks there could be a significant shake-up in the most senior ranks of the company, Anderson said in a research note.

Rose said the company will announce the members of the executive committee of the combined Merck/Schering-Plough, and senior management, as the close of the merger nears.

(Reporting by Lewis Krauskopf; editing by John Wallace)