Vaccines for preventing influenza in people with asthma.
BACKGROUND: Influenza vaccination is recommended for asthmatic patients in many countries as observational studies have shown that influenza infection can be associated with asthma exacerbations, but influenza vaccination itself has the potential to adversely affect pulmonary function. A recent overview concluded that there was no clear benefit of influenza vaccination in patients with asthma but this conclusions was not based on a systematic search of the literature. OBJECTIVES: Whilst influenza may cause asthma exacerbations, there is controversy about the use of influenza vaccinations, since they may precipitate an asthma attack in some people. The objective of this review was to assess the effects of influenza vaccination in children and adults with asthma. SEARCH STRATEGY: We searched the Cochrane Airways Group trials register and checked reference lists of articles. SELECTION CRITERIA: Randomised trials of influenza vaccination in children (over two years of age) and adults with asthma. Studies involving people with chronic obstructive pulmonary disease were excluded. DATA COLLECTION AND ANALYSIS: Inclusion criteria and assessment of trial quality were applied by two reviewers independently. Data extraction was done by two reviewers independently. Study authors were contacted for missing information. MAIN RESULTS: Nine trials were included. Four of these trials were of high quality. One further article has been included since the previous version of this review. Inclusion of the new trial has not altered the conclusions of this review. The included studies covered a wide diversity of people, settings and types of influenza vaccination, so data from the different trials were not pooled. In one trial, no protective effect of influenza vaccination against asthma exacerbation was demonstrated, but the incidence of influenza was low during the study period. A higher number of asthma exacerbations following killed influenza vaccination was found in one trial (risk difference 3 1%, 95% confidence interval 0.3% to 5.8%). When people with upper respiratory tract infections were excluded, this difference was no longer significant. A small trial using recombinant vaccine found no significant difference in asthma exacerbations between the vaccinated and placebo groups. REVIEWER'S CONCLUSIONS: There is not enough evidence to assess the benefits and risks of influenza vaccination for people with asthma.