UPDATE 2-US FDA wants panel to probe Pfizer vaccine efficacy

* Prevnar 13 study misses on three strains

* FDA to ask advisory panel about efficacy results

* Pfizer says overall data show vaccine effective

(Recasts; Adds company, analyst comment)

By Lisa Richwine

WASHINGTON, Nov 16 (Reuters) - Pfizer Inc's (PFE.N: 行情) next- generation Prevnar vaccine missed some of the main goals in a study testing its ability to protect against bacteria that cause ear infections, pneumonia and other diseases, U.S. reviewers said in documents released on Monday.

Pfizer said the overall data showed the experimental Prevnar 13 shot was effective against a wider range of illness than the original vaccine and the company would make that case to an advisory panel that meets on Wednesday.

The new version is designed for immunizing infants and toddlers against 13 forms of a bacterium called streptococcus pneumoniae, or pneumococcus, that cause an array of illnesses.

The vaccine was the most important product in the pipeline of Wyeth, which Pfizer recently acquired. The Food and Drug Administration is weighing whether to approve Prevnar 13 for sale.

The original Prevnar was introduced in 2000 and has annual sales around $3 billion. It fights seven pneumococcal types.

Wyeth studied whether levels of antibodies that fight infection were equivalent, or "non-inferior," between Prevnar and Prevnar 13.

For three of the types, "the non-inferiority criterion was not met" for some people in the study, FDA reviewers said in an analysis prepared for an outside advisory committee.

The reviewers said they would ask the advisory panel about the clinical trial findings.

Pfizer, in a separate summary also released by the FDA, said overall results showed Prevnar 13 provided "a real and substantial benefit given its demonstrated ability to elicit immune responses" to each of the 13 types.

The company also said the vaccine was "well tolerated and as safe as Prevnar."

Dr. Emilio Emini, Pfizer's chief scientific officer for vaccine research, said World Health Organization guidelines for testing pneumococcal vaccines state that reaching all of the non-inferiority goals is not a requirement if other measures are achieved.

Morgan Stanley analyst David Risinger expected the advisory panel to recommend approval for Prevnar 13.

Risinger said in a research note he thought the panel would be swayed in part by data showing the newer vaccine protected against a strain known as 19A, currently the most common cause of pneumococcal infections in the United States.

Emini said the data under FDA review was the same that was scrutinized by the European Medicines Agency, which recommended approval of the vaccine in Europe. A final decision from the European Commission is still pending.

Wyeth had been due to receive a decision in the United States in September, but the company announced in August the review was extended by three months to Dec. 30.