This review presents the available documentation of the health effects of influenza vaccination to the elderly and people suffering from chronic illness.

We searched for systematic reviews of the effects of influenza vaccine to the elderly and chronic ill. We updated the systematic reviews that we included, and we searched for randomized controlled trials (RCTs) of the effect of influenza vaccine to people with chronic illness. We included the following outcomes; all cause mortality, complications due to influenza (pneumonia), hospital admissions, influenza (laboratory confirmed), influenza like illness and adverse events.

We included five systematic reviews that assessed the effect of influenza vaccination to the elderly, to people with chronic obstructive lung disease, asthma, bronchiectasis, and cystic fibrosis. We included one RCT and 12 observational studies for update of the effect of influenza vaccination on elderly. We additionally included four RCTs where the effect had been measured in people with cirrhosis of the liver, multiple sclerosis, HIV-infection, and cardio vascular disease.

The evidence for influenza vaccine to elderly included more than 2.5 million people who had been included in six RCTs and 60 observational studies. Results indicate that influenza vaccine possibly reduce the risk of influenza and influenza like illness for community dwelling elderly. Influenza vaccine does possibly not influence the risk of all cause mortality or pneumonia for community dwelling elderly. Influenza vaccine possibly reduce the risk of influenza like illness for elderly living in institution, people with chronic hearth disease and people with HIV-infection. The quality of the evidence is low and very low, and results are uncertain. For the other outcomes and the other chronic diseases, evidence were either lacking or of very low quality.

The evidence regarding effect of influenza vaccine to elderly and people with chronic illness is sparse.