NEW YORK (Reuters Health) - Currently U.S. adults over the age 65 are advised to get a pneumococcal vaccine to protect against serious infections, but a large new study suggests the vaccine does not cut the risk of pneumonia.

However, the vaccine does reduce an older adult's risk for potentially life-threatening blood infection with pneumococcal bacteria, scientists reported Wednesday in The New England Journal of Medicine.

The vaccine protects against 23 strains of pneumococcus, a type of bacteria that sickens 60,000 people a year with severe infections -- 20,000 over age 65. Another 175,000 contract pneumonia and are hospitalized, and 3,000 to 6,000 get meningitis from the bacteria.

Until now, it wasn't clear whether the vaccine reduced the risk of pneumonia overall, explained the study's lead author Dr. Lisa A. Jackson of Group Health Cooperative in Seattle, Washington.

"One previous retrospective study indicated that the vaccine did prevent pneumonia. However, several clinical trials have not shown that the vaccine reduced the risk of pneumonia," Jackson said.

"Those trials were in general too small, though, to have a very good ability to show a protective effect of vaccination," she added.

To investigate further, Jackson's team assessed three years of medical records from a group of 47,365 men and women ages 65 years and older. The records also contained information about whether or not they had received the pneumococcal vaccine.

The authors identified 1,428 people who had been hospitalized with pneumonia, 3,061 who had pneumonia that did not require hospitalization and 61 people who had blood infections due to pneumococcal bacteria.

While the risk of pneumococcal blood infections was 44 percent lower in people who had been vaccinated, people who got the vaccine had a slightly higher chance of being hospitalized for pneumonia. Vaccination did not seem to have any effect on the overall odds of developing pneumonia.

"We found that the vaccine reduces the risk of bloodstream infection (bacteremia) with the pneumococcal bacteria," said Jackson.

"Bloodstream infection is the most serious type of pneumococcal infection but accounts for only a very small percentage of all (pneumococcal infections). We did not find that the vaccine reduces the risk of pneumonia overall," said Jackson.

Jackson noted that the new findings are consistent with previous studies indicating that the vaccine prevents bloodstream infections, so the new results support the current vaccination recommendations.

"The vaccine doesn't reduce the overall risk of pneumonia, which tells us that further research is needed to identify different vaccines that may reduce the risk of pneumonia, which is a very common health problem in seniors," Jackson added.

On the bright side, Jackson told Reuters Health that there is another way seniors can reduce their risk of pneumonia.

"Getting the flu shot every year will reduce the risk of pneumonia that is a consequence of influenza infection," said Jackson.

"Seniors should get the pneumococcal vaccine because it prevents bloodstream infection and should also get their annual flu shot," she said.

"Researchers," Jackson continued, "should increase their efforts to identify vaccines that will be effective in preventing pneumonia overall."

Commenting on the study, Dr. Cynthia Whitney, a medical epidemiologist for the Centers for Disease Control and Prevention's respiratory diseases branch, told Reuters Health that there were always questions about pneumonia prevention.

"I think the study provides more evidence (that the pneumococcal vaccine is) not working against pneumonia," said Whitney.

Nonetheless, Whitney believes that the findings do support current vaccination recommendations. The vaccine is recommended for all adults over age 65 and people under 65 with chronic illnesses.

"The results show it prevents severe disease -- pneumococcal bacteremia -- but it also suggests it didn't prevent pneumonia, a common cause of death in older people," said Whitney.

"It means we're going to need other tools. We should go on and develop better vaccines if we're going to prevent pneumonia," she added.

Whitney noted that research on vaccinations that prevent pneumonia should be a top priority.

SOURCE: The New England Journal of Medicine 2003;348:1747-1755.