Flu Vaccine Didn't Cut Pneumonia Risk

Abstract

Fran Lowry is with the Orlando, Fla., bureau of Elsevier Global Medical News. Influenza vaccination was not associated with a significantly reduced risk of community-acquired pneumonia in a large population of people aged 65 and older. In the study of 1,173 cases and 2,346 controls, flu vaccine was associated with an 8% lower risk of community-acquired pneumonia among immunocompetent seniors during influenza season, investigators reported in The Lancet. The finding stands in contrast to a number of observational studies that suggest that vaccination substantially reduces the risk of hospital admission due to pneumonia in elderly adults. But these studies have not differentiated between healthy, mobile, immunocompetent seniors and frail seniors of advanced age or chronic health conditions, who are known to benefit from influenza vaccine. The investigators conducted a nested case-control study of individuals aged 65-94 years who were enrolled in Group Health, a health maintenance organization in Seattle, during 2000, 2001, and 2002. To ensure that they were removing any bias in their results, the researchers looked at both the preinfluenza and influenza periods of each year, reasoning that any benefit from the flu vaccine that was seen in the preinfluenza season could not be due to the protective effects of the vaccine. They found that in the preinfluenza season, there was an apparent strong benefit of the vaccine, with a 40% reduction in the risk of pneumonia. But after controlling for the presence of frail and sick seniors, they found essentially no effect of influenza vaccine during preinfluenza periods, reported the researchers, led by Michael L. Jackson, PhD, of the Group Health Center for Health Studies, Seattle (Lancet 2008;372:398-405). To look at the effect of the flu vaccine during influenza periods, they selected subjects who were immunocompetent and had no serious comorbidities. The age- and sex-adjusted odds ratio for the association between influenza vaccination and risk of community-acquired pneumonia was 1.04, but after adjustment for the confounding factors that were identified in the preinfluenza periods, the influenza season odds ratio was 0.92. In an interview, Dr. Jackson said that the findings are consistent with there being no link between flu vaccine and pneumonia risk in seniors. However, this does not mean that they should forego flu shots. “Randomized trials, which are the gold standard for public health-related evidence, have found that influenza vaccine reduces the risk of influenza infection in young—that is, 75 years and younger—healthy seniors. So they should still get their flu shots,” he said. He added that more work needs to be done to understand how well the vaccine prevents serious complications of the flu, such as pneumonia, in older seniors and those with chronic health problems. In an accompanying commentary, Edward A. Belongia, MD, of the Marshfield (Wis.) Clinic Research Foundation, and David K. Shay, MD, of the influenza division, Centers for Disease Control and Prevention, agreed with the need for additional studies about the causes of pneumonia in elderly adults, particularly in highly vaccinated populations (Lancet 2008;372:352-4). Calling the study by Dr. Jackson and his colleagues “well designed,” they added that standard methods of comparing the effectiveness of flu shots in different seasons and in different populations are also needed. The commentators also suggested that future studies of vaccine effectiveness should include other flu-related acute illnesses besides pneumonia and use sensitive and specific diagnostic tests, such as the polymerase chain reaction, for influenza. Dr. Belongia is director of the Epidemiology Research Center at the Marshfield Clinic Research Foundation. One of the authors of the study disclosed that she is a paid consultant to Sanofi Pasteur and to Novartis, manufacturers of the influenza vaccine. The other authors declared no conflict of interest.