The trial results, expected next year, along with data on whether use of the vaccine in children is affecting rates of disease in adults, will be assessed before a recommendation is made, said CDC spokeswoman Alison Patti.

The Food and Drug Administration in December approved use of Prevnar 13 in older adults and Pfizer said it still expects to begin a marketing campaign in March.

A trial currently underway in the Netherlands is designed to prove that the vaccine prevents pneumonia in adults.

Pfizer said use of the vaccine in adults will be influenced by the advisory committee's decision, but it is not changing its 2012 financial outlook.

Wall Street analysts, on average, have forecast Prevnar 13 sales of $4.42 billion this year, rising to $6.75 billion by 2016.

"We are committed to continuing discussions with the CDC about a recommendation concerning the use of Prevnar 13 in adults 50 years of age and older," said Pfizer spokeswoman Victoria Davis.

Prevnar, currently a $3.7 billion-a-year vaccine used to prevent infections with the streptococcus bacteria, got U.S. approval in 2010 for use in infants and children under the age of 6.

(Reporting By Deena Beasley; Editing by Tim Dobbyn)

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