Effects of influenza vaccination on clinical outcomes of chronic obstructive pulmonary disease: A systematic review and meta-analysis

•Evidence for that influenza vaccination improves outcomes of COPD is insufficient.•We include eligible studies regardless of design with GOLD diagnosis criteria of COPD.•Influenza vaccination reduces exacerbations and trends of hospitalizations of COPD.•COPD patients with severe airflow limitation benefit more from influenza vaccination.•Influenza vaccination is recommended for all COPD patients especially for GOLD 3–4. Influenza is a threat to patients with chronic obstructive pulmonary disease (COPD), influenza vaccination help to reduce incidence of influenza infection, however, whether it is beneficial to COPD patients in clinical outcomes lacks for evidence due to limited studies and participations. We searched PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure (CNKI) and China Science and Technology Journal Database (CSTJ) to retrieve eligible studies regardless of study design published before August 2020, and conducted meta-analysis with odds ratio (OR) and mean difference (MD). The quality of included studies and pooled evidences were assessed. Narrative summaries were provided where data were insufficient for meta-analysis. 2831 COPD patients were included, the pooled results showed that influenza vaccination reduced the exacerbations (P = 0.0001) and trends of hospitalizations (P = 0.09) in COPD patients. Further subgroup analysis showed that the reduction of exacerbations and hospitalizations were significant in patients with FEV1