The effect of influenza vaccination on the risk of pneumonia in immunocompetent elderly people during influenza seasons might be less than previously estimated. This is the conclusion of authors of an Article in this week's edition of The Lancet.
Pneumonia is a common complication of influenza infection in elderly individuals and could therefore potentially be prevented by influenza vaccination. Studies have shown that vaccinated elderly people had a 20-30% reduced risk of admission for pneumonia compared with elderly people who have not been vaccinated -- however, these findings could have been biased by underlying differences in health between the groups studied. Also, since most people with pneumonia are not treated in hospital, such studies should include both outpatient and inpatient cases. Dr Michael Jackson, Group Health Center for Health Studies, Seattle, WA, USA and colleagues assessed whether influenza vaccination is associated with a risk of community-acquired pneumonia in immunocompetent elderly people after controlling for health status indicators.
The study involved elderly people aged 65-94 years enrolled in Group Health Cooperative (a health maintenance organisation) during the 2000, 2001 and 2002 preinfluenza periods and influenza seasons. Cases of inpatient or outpatient pneumonia were validated by review of medical records or chest radiograph report. Two age-matched and sex-matched controls were randomly selected for each case. Medical records were also reviewed to define potential confounders, ie, factors that could have influenced the findings, including smoking history, presence and severity of lung and heart disease, and frailty indicators.
The researchers investigated 1173 cases of community-acquired pneumonia and 2346 controls. After the results were adjusted for the confounding effects of the presence and severity of other diseases in the patients, as defined by chart review, influenza vaccination was not associated with a reduced risk of community-acquired pneumonia.
The authors conclude: "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."
In an accompanying Comment, Dr Edward Belongia, Marshfield Clinic Research Foundation, Wisconsin, and Dr David Shay, Influenza Division, US Centres for Disease Control and Prevention, Atlanta, GA, USA, say: "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."
Dr Edward Belongia, Marshfield Clinic Research T) +1 715-387-9362 E) firstname.lastname@example.org