UPDATE 2-U.S. review of Pfizer vaccine not completed

* Deadline for Prevnar 13 decision had been Wednesday

* Pfizer says remains confident in data

* Pfizer shares down 2 cents in after-hours trading (Adds FDA no comment, background, shares)

NEW YORK, Dec 30 (Reuters) - U.S. health regulators have not yet completed their review of a more protective form of Pfizer Inc's (PFE.N) big-selling Prevnar vaccine that fights pneumonia and meningitis, the drugmaker said on Wednesday.

A decision by the U.S. Food and Drug Administration on Prevnar 13 had been expected by Wednesday. The review will continue, the company said. An FDA spokeswoman said the agency's policy is not to comment on ongoing reviews.

"We remain confident that the data in the (application) support the approval of Prevnar 13," Emilio Emini, Pfizer's chief scientific officer for vaccine research, said in a statement. "We will continue to work closely with the FDA to help expedite the completion of its review."

Prevnar was one of the major franchises that Pfizer obtained in its $67 billion acquisition of Wyeth, which closed in October and helps the world's largest drugmaker diversify into vaccines and biotechnology medicines.

Analysts expect Prevnar 13 sales to reach nearly $4 billion a year by 2013, according to the consensus forecast compiled by Thomson Pharma.

The new product is designed to protect against 13 serotypes, or forms, of a bacterium called streptococcus pneumoniae (pneumococcus) that can cause illnesses ranging from ear infections to pneumonia and meningitis. Pfizer is seeking approval for use in infants and toddlers.

The original Prevnar, which fights seven pneumococcal strains, was introduced in 2000.

A U.S. FDA advisory panel voted 10-1 in November that Prevnar 13 was safe and effective for infants and toddlers. The agency usually approves products backed by its advisory committees.

Prevnar 13 in May won a priority review designation, which is given to products that would be a significant improvement in addressing serious or life-threatening diseases.

In August, the FDA extended its review by 90 days from Sept. 30 to Dec. 30, based on additional manufacturing data requested by the agency.

European regulators approved the new form of Prevnar earlier this month. It has been approved in 34 countries.

GlaxoSmithKline (GSK.L) has a rival vaccine, called Synflorix, that is active against 10 strains. Synflorix is approved in Europe and some other markets, but not the United States. Glaxo has said it does not have plans at this time to seek approval in the United States for the product.

Pfizer shares fell 2 cents to $18.48 in after-hours trading. They earlier closed down 6 cents at $18.50 on the New York Stock Exchange.

(Reporting by Lewis Krauskopf; Additional reporting by Karey Wutkowski in Washington; Editing by Matthew Lewis and Richard Chang)