Pfizer, the world's biggest drugmaker, is recalling one batch of its Prevnar pneumonia vaccine because it was filled with expired material, U.S. drug regulators said.

Pfizer began the recall on February 10, the Food and Drug Administration said on its website on Tuesday. The recall affected just one wholesaler, meaning the medicine had not yet reached doctors.

Prevnar 13 fights pneumonia, meningitis and other diseases caused by pneumococcus bacteria, and was recently approved for use in adults 50 and older. It had previously been approved for children.

Pneumonia caused by the pneumococcal organism is one of the biggest causes of death in older people and its incidence begins to increase after age 50. The FDA has said about 300,000 older adults in the United States are hospitalized each year for pneumonia.

The vaccine is poised to become one of Pfizer's biggest brands. Wall Street analysts, on average, have forecast Prevnar 13 sales of $4.42 billion this year, rising to $6.75 billion by 2016.

The recalled Prevnar syringes had been labeled as expiring on September 30, 2013 and had the lot number F73652, the FDA said.

Pfizer said it continually monitors the safety of all of its medicines, and does not believe the recalled doses posed any risk to health.