(Reuters) - Pfizer Inc on Friday said U.S. regulators had approved wider use of its Prevnar 13 vaccine to prevent infections with pneumococcal bacteria, for children and adolescents aged 6 years to 17 years.

The product was already approved in the United States to prevent infections among children aged 6 weeks through 5 years. It is also approved for adults aged 50 and older.

The vaccine protects against infection with 13 strains of the Streptococcus pneumoniae bacterium. The bacterium can cause pneumonia, ear infections and other problems.

Prevnar 13 has annual sales of about $3.5 billion, making it Pfizer's third-biggest brand. It was approved in 2010, and has largely displaced an older vaccine called Prevnar, which protected against only 7 prevalent strains of the bacterium.

(Reporting by Ransdell Pierson; Editing by David Gregorio and Dan Grebler)