Effectiveness of influenza vaccines in asthma: a systematic review and meta-analysis.

There is uncertainty about the effectiveness of influenza vaccination in people with asthma and its impact on asthma outcomes, which may contribute to the sub-optimal vaccination rates in people with asthma. This systematic review and meta-analysis involved searching 12 international databases for randomized controlled trials (RCTs) and high quality quasi-experimental and epidemiological studies (1970 to 2016). The risk of bias was low for three included RCTs. The quality of three included observational studies was moderate. The quality of evidence was very low for all study outcomes. Pooled vaccine effectiveness in 1,825 people with asthma from two test-negative design case-control studies was 45% (95% CI 31 to 56) for laboratory-confirmed influenza. Pooled efficacy of live vaccines in reducing influenza was 81% (95% CI 33 to 94). Live vaccine reduced febrile illness by 72% (95% CI 20 to 90). Influenza vaccine prevented 59-78% of asthma attacks leading to emergency visits and/or hospitalizations. For people with asthma influenza vaccination may be effective in both reducing influenza infection and asthma attacks