Well, that could have been embarrassing. Pfizer (NYSE:PFE) bought Wyeth in large part for one of its top-selling products -- pneumococcal vaccine Prevnar. Now, just a month later, the newly merged pharmaceutical giant faces a potential disappointment over the product's next generation, Prevnar 13. Fortunately, the vaccine seems to have slipped through its Food and Drug Administration advisory committee unscathed.

Prevnar 13 covers -- you guessed it -- 13 different types of pneumococcal disease, six more than the original. In order to gain approval, Wyeth tested the new vaccine against the old version, but Prevnar 13 failed to show that it was as good as the original for three of the strains in some patients.

The FDA asked a panel of experts for their opinion on how important the failure was. But they shrugged it off at a meeting yesterday, voting 10-1 that the vaccine is safe and effective.

Now the ball is back in the FDA's hands. The agency doesn't have to follow the committee's advice, but I have a hard time imagining that it won't approve the vaccine, given such resounding support. The PDUFA date for the vaccine is Dec. 30, so perhaps an early Christmas present is in order.

Pfizer is competing globally against rival Synflorix from GlaxoSmithKline (NYSE:GSK), but Prevnar currently has the U.S. market all to itself, since Synflorix isn't approved here yet. Prevnar is currently just used in children, but Prevnar 13 is being tested in adults in an effort to compete with Merck's (NYSE:MRK) Pneumovax 23, which is approved to treat adults in the U.S.

I liked Pfizer's move into immunizations with its acquisition of Wyeth. As Glaxo, Novartis (NYSE:NVS), sanofi-aventis (NYSE:SNY) and others have shown, vaccines can be lucrative. However I still didn't think Wyeth was cheap enough to justify an acquisition from Pfizer. In order to prove me wrong, Pfizer will need to continue to push drugs through the pipeline.