A vaccine typically used to fight childhood infections could prevent pneumonia in over 65s.

The researchers looked at 85,000 patients in a study called CAPiTA and found the drug Prevnar 13 prevented infections from the Streptococcus pneumoniae bacteria, Reuters reported.

"We expect the U.S. and other developed markets to broadly recommend adult use of the product," J.P. Morgan analyst Chris Schott said in a research note, Reuters reported.

About 300,000 adults over the age of 50 are hospitalized for pneumococcal pneumonia every year; many cases prove to be fatal. The drug which was shown to fight these infections is one of Pfizer's biggest products and earns the company about $4.4 billion.

Prevnar 13 was first approved to prevent Streptococcus pneumoniae bacteria-related infections such as ear infections, pneumonia, and meningitis in children. The vaccine was approved for adult aged 50 and older in 2011; the approval would only be held if the CAPiTA results proved favorable.

"Favorable data from the study are expected to be added to the package insert label of Prevnar 13, greatly boosting the attractiveness of the vaccine to doctors with elderly patients," Reuters.

Tim Anderson, an analyst with Sanford Bernstein & Co told Reuters he expected Prevnar 13 sales to raise to $1.3 billion by 2020 total sales of the Prevnar franchise to be at $6 billion by that time. The vaccine has only been given to a limited number of adult patients.

The standard pneumonia vaccine called Pneumovax from Merck & Co is approved for both children and  adults 50 years and older.

"Pneumococcal pneumonia is a significant cause of illness and death in adults around the world, and the potential to reduce the burden of this disease through direct vaccination of adults represents a meaningful public health benefit," Emilio A. Emini, Pfizer's senior vice president of vaccine research and development, told the Wall Street Journal.