In immunocompetent elderly people, influenza vaccine might not protect against pneumonia in influenza seasons than previously expected, according to an article released on August 1, 2008 in The Lancet.
Influenza is a viral disease that usually occurs in regular seasonal epidemics. As it is an RNA-virus, mutation is frequent, so new influenza viruses, similar to one another, often challenge the immune system in each new year. As a result, the flu vaccine is administered yearly for a predicted set of strains meant to protect against that year’s mixture.
A common complication of influenza infection in the elderly is pneumonia, and previous work has shown a 20-30% decreased risk of pneumonia complications in vaccinated individuals. However, these studies were performed in different populations, so observed differences could have been caused by underlying variety between the populations. Additional studies should also incorporate inpatient and outpatient cases of pneumonia, because most of these are not treated in the hospital.
To evaluate the true impact of influenza vaccination on community-acquired pneumonia Dr Michael Jackson, Group Health Center for Health Studies, Seattle, WA, evaluated the medical records of 65-94 year olds enrolled in Group Health Cooperative during the 2000, 2001, and 2002 in the influenza seasons and preinfluenza periods. The researchers verified the diagnosis using the medical records and examination of a chest radiograph report. Age and sex matched controls were randomly selected for each case. Additionally, medical records were examined for potential confounders which might make it seem like there is a correlation when in reality there is none, such as smoking, lung disease, and various frailty indicators.
In total, 1,173 community-acquired pneumonia were examined alongside 2,346 controls. After adjusting for the identified confounding effects and severity of other diseases in the patients, influenza vaccination was not associatd with reducting the risk of pneumonia. They authors say: “These results could mean that influenza infection only causes a small proportion of the pneumonias in these people, so that reduction of the risk of influenza infection does not lead to an important reduction in all-cause pneumonia. Alternatively, these results could mean that the vaccine is not very effective in reducing the risk of influenza infection in elderly people at risk of pneumonia. These two possibilities have quite different implications for vaccine development and vaccination recommendations; differentiation between them will need studies with laboratory-confirmed endpoints, such as pneumonia or serious respiratory outcomes after a confirmed influenza infection.”
Dr Edward Belongia, Marshfield Clinic Research Foundation, Wisconsin, and Dr David Shay, Influenza Division, US Centres for Disease Control and Prevention, Atlanta, GA, USA, contributed an accompanying comment in which they state note the new nature of this study: “More studies that use laboratory-confirmed outcomes and adjust for a broad range of confounding variables will provide valuable information about the effects of antigenic match and other factors that affect vaccine effectiveness in elderly adults.”
Influenza vaccination and risk of community-acquired pneumonia in immunocompetent elderly people: a population-based, nested case-control study
Michael L Jackson, Jennifer C Nelson, Noel S Weiss, Kathleen M Neuzil, William Barlow, Lisa A Jackson
Lancet 2008; 372: 398-405
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Written by Anna Sophia McKenney