THURSDAY, July 31, 2008 (HealthDay News) -- Flu vaccine may not protect older people from pneumonia once they get the disease, researchers report.
Older, frail adults are more susceptible to getting the flu, even if they have been vaccinated, and once getting the flu, they are more susceptible to such complications as pneumonia. It had been thought that flu vaccine would prevent flu -- and pneumonia -- across all groups of seniors, but this benefit appears to be largely confined to younger, healthier seniors.
"In seniors, flu vaccine was not linked to a reduced risk of pneumonia," said lead researcher Michael L. Jackson, a postdoctoral fellow at the Group Health Center for Health Studies in Seattle.
Jackson still recommends that seniors get flu vaccine, however. "There have been good randomized trials that show, at least in healthy seniors, that the vaccine reduces the risk of influenza," he said. "However, earlier studies have overestimated how well the vaccine works in reducing complications of influenza. So, the vaccine may not reduce the risk of complications as much as previously thought," he said.
Among young healthy seniors, the vaccine reduces the risk of flu, Jackson said. "When you look at the total population of seniors, which includes people over 75 and people that have chronic health diseases -- lung disease, heart disease, diabetes, and things like that -- we don't know if the vaccine is effective in the seniors," he said. "People with these chronic diseases are more susceptible to getting the flu, and they are more likely to develop pneumonia if they do get influenza."
The report is published in the Aug. 2 issue of The Lancet.
For the study, Jackson's team collected data on 1,173 people between the ages of 65 and 94 who developed pneumonia They compared these individuals with 2,346 people who did not get pneumonia. Both groups had similar rates of flu vaccination over the three seasons of studies, the researchers say.
The researchers found that vaccinated seniors who got the flu were as likely to develop pneumonia as unvaccinated seniors who got the flu.
Dr. Pascal James Imperato, dean of the master of public health program at the State University of New York Downstate Medical Center in New York City, was not surprised by these results.
"We know that elderly people do not form sufficient antibodies to certain vaccines, the flu vaccine included," Imperato said. "In addition, people in their 70s and 80s and 90s are more prone to pneumonia with or without influenza. A number of these pneumonias may be secondary to other causes aside from influenza."
Even though many of the elderly will not develop sufficient antibodies to the flu vaccine, getting the shot is still worthwhile, Imperato said. "Having many people vaccinated builds up a herd immunity to disease, and you create barriers to transmission," he added.
Dr. Marc Siegel, a clinical associate professor of medicine at New York University School of Medicine in New York City, said the results of this study fly in the face of prevailing wisdom.
Siegel noted that 36,000 people in the United States die each year from the flu. "Over 90 percent of them are elderly," he said. "We give the flu shot primarily to prevent elderly deaths.
The effectiveness of the flu vaccine varies year to year, however, depending on how good a match it is for the circulating strains of influence. "In the best years, the flu vaccine is really only 40 to 60 percent effective," Siegel added.
In addition, Siegel thinks that the flu vaccine protects against other complication including respiratory diseases, which can also be fatal. "There are plenty of flu-related complications that are life-threatening besides pneumonia," he said.
"This study is a reminder that flu vaccines are not a panacea, but they are valuable, because they cut down on the incidence of influenza," Siegel said. "Flu shots definitely cut down on the number of flu-related deaths."
For more about seasonal flu vaccine, visit the U.S. Centers for Disease Control and Prevention.