Allergen immunotherapy for allergic asthma: A systematic review and meta‐analysis

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>To inform the development of the European Academy of Allergy and Clinical Immunology's (<jats:styled-content style="fixed-case">EAACI</jats:styled-content>) Guidelines on Allergen Immunotherapy (<jats:styled-content style="fixed-case">AIT</jats:styled-content>) for allergic asthma, we assessed the evidence on the effectiveness, cost‐effectiveness and safety of <jats:styled-content style="fixed-case">AIT</jats:styled-content>.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We performed a systematic review, which involved searching nine databases. Studies were screened against predefined eligibility criteria and critically appraised using established instruments. Data were synthesized using random‐effects meta‐analyses.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>98 studies satisfied the inclusion criteria. Short‐term symptom scores were reduced with a standardized mean difference (<jats:styled-content style="fixed-case">SMD</jats:styled-content>) of −1.11 (95% <jats:styled-content style="fixed-case">CI</jats:styled-content> −1.66, −0.56). This was robust to a prespecified sensitivity analyses, but there was evidence suggestive of publication bias. Short‐term medication scores were reduced <jats:styled-content style="fixed-case">SMD</jats:styled-content> −1.21 (95% <jats:styled-content style="fixed-case">CI</jats:styled-content> −1.87, −0.54), again with evidence of potential publication bias. There was no reduction in short‐term combined medication and symptom scores <jats:styled-content style="fixed-case">SMD</jats:styled-content> 0.17 (95% <jats:styled-content style="fixed-case">CI</jats:styled-content> −0.23, 0.58), but one study showed a beneficial long‐term effect.</jats:p><jats:p>For secondary outcomes, subcutaneous immunotherapy (<jats:styled-content style="fixed-case">SCIT</jats:styled-content>) improved quality of life and decreased allergen‐specific airway hyperreactivity (<jats:styled-content style="fixed-case">AHR</jats:styled-content>), but this was not the case for sublingual immunotherapy (<jats:styled-content style="fixed-case">SLIT</jats:styled-content>). There were no consistent effects on asthma control, exacerbations, lung function, and nonspecific <jats:styled-content style="fixed-case">AHR</jats:styled-content>.</jats:p><jats:p><jats:styled-content style="fixed-case">AIT</jats:styled-content> resulted in a modest increased risk of adverse events (<jats:styled-content style="fixed-case">AE</jats:styled-content>s). Although relatively uncommon, systemic <jats:styled-content style="fixed-case">AE</jats:styled-content>s were more frequent with <jats:styled-content style="fixed-case">SCIT</jats:styled-content>; however no fatalities were reported.</jats:p><jats:p>The limited evidence on cost‐effectiveness was mainly available for sublingual immunotherapy (<jats:styled-content style="fixed-case">SLIT</jats:styled-content>) and this suggested that <jats:styled-content style="fixed-case">SLIT</jats:styled-content> is likely to be cost‐effective.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p><jats:styled-content style="fixed-case">AIT</jats:styled-content> can achieve substantial reductions in short‐term symptom and medication scores in allergic asthma. It was however associated with a modest increased risk of systemic and local <jats:styled-content style="fixed-case">AE</jats:styled-content>s. More data are needed in relation to secondary outcomes, longer‐term effectiveness and cost‐effectiveness.</jats:p></jats:sec>