Pfizer Inc said the U.S. Food and Drug Administration had expanded the use of its best-selling pneumonia vaccine, Prevnar, to adults aged 18 through 49.

The vaccine, which is already approved for use in adults aged 50 and above, and children aged 6 weeks to 17 years, prevents invasive diseases caused by 13 Streptococcus pneumoniae strains.

The regulator's decision is based on data from a late-stage study in adults who had not been vaccinated against the disease previously.

Prevnar has been buoying Pfizer's revenue, helping the company beat Wall Street estimates.

The Prevnar range of products grossed annual sales of $6.25 billion in 2015, up 40 percent from a year earlier.

Pneumococcal pneumonia, caused when the bacterium streptococcus pneumoniae infects the lungs, is the most common disease caused by this bacterium in adults.

When the bacterium invades parts of the body that are normally free from germs, such as the blood or spinal fluid, the disease is considered "invasive."