The pneumonia vaccine, which is recommended for all adults over 65 years of age, does not reduce the risk of contracting the disease, researchers said.

Each year, some 350,000 to 620,000 elderly Americans are hospitalized with pneumonia and one-third to one-half have a type known as pneumococcal pneumonia.

However, since the pneumococcal pneumonia immunization targets the bacteria that cause the pneumonia and other diseases, it is only effective when the bacteria, Streptococcus pneumoniae, get into the bloodstream.

But, the bloodstream form of the disease, pneumococcal bacteremia, is relatively uncommon. Only about 60 out of 100,000 seniors contract this form of the disease. Among this small group, the vaccine reduces the risk of contracting the disease by about 50 percent.

In the largest study to date of the pneumococcal pneumonia vaccine, researchers examined medical data on 47,365 people aged 65 years and older from 1998 through 2001.

Researchers found that 1,428 people had been hospitalized with pneumonia, 3,061 had pneumonia but did not require hospitalization and 61 people had blood infections due to pneumococcal bacteria.

No association was found between pneumococcal vaccination and a reduced risk of pneumonia from any cause, researchers said.

The findings did show that the vaccination is effective in preventing disease caused by pneumococcal bacteria, so researchers say the current vaccination recommendations are accurate.

Further research is needed to identify vaccines that will be effective in preventing pneumonia overall, researchers noted.

Pneumonia affects about 1 million elderly people each year, and pneumonia and influenza combined are the fifth-leading cause of death in older adults.

The New England Journal of Medicine May 1, 2003;348:1747-1755