Abstract: We identified 14 studies that met our inclusion criteria, with a total of 6641 randomised participants, of whom 5638 completed the study. All studies lasted between two and 78 weeks and showed good methodological quality overall. We included 10 comparisons in this review, seven for which the dose of VI and FF was 100/25 mcg (VI/FF 100/25 mcg vs placebo; VI/FF 100/25 mcg vs same dose of FF; VI/FF 100/25 mcg vs same dose of VI; VI/FF 100/25 mcg vs fluticasone propionate (FP) 500 mcg twice-daily; VI/FF 100/25 mcg vs fluticasone propionate/salmeterol (FP/SAL) 250/50 mcg twice-daily; VI/FF 100/25 mcg vs FP/SAL 250/25 mcg twice-daily; FF/VI 100/25 vs FP/SAL500/50) and three for which the dose of VI and FF was 200/25 mcg (VI/FF 200/25 mcg vs placebo; VI/FF 200/25 mcg vs FP 500 mcg; VI/FF 200/25 mcg vs same dose of FF). We found very few opportunities to combine results from the 14 included studies in meta-analyses. We tabulated the data for our pre-specified primary outcomes. In particular, we found insufficient information to assess whether once-daily VI/FF was better or worse than twice-daily FP/SAL in terms of efficacy or safety. Only one of the 14 studies looked at health-related quality of life when comparing VI and FF 100/25 mcg versus placebo and identified a significant advantage of VI/FF 100/25 mcg (mean difference (MD) 0.30, 95% confidence interval (CI) 0.14 to 0.46; 329 participants); we recognised this as moderate-quality evidence. Only two studies compared VI/FF 100/25 mcg versus placebo with respect to exacerbations; both studies reported no exacerbations in either treatment arm. Five studies (VI/FF 100/25 mcg vs placebo) sought information on serious adverse events; all five studies reported no serious adverse events in the VI/FF 100/25 mcg or placebo arms. We found no comparison relevant to our primary outcomes for VI/FF at a higher dose (200/25 mcg) versus placebo. The small number of studies contributing to each comparison precludes the opportunity to draw robust conclusions for clinical practice. These studies were not of sufficient duration to allow conclusions about long-term side effects. Some evidence suggests clear advantages for VI/FF, in combination, compared with placebo, particularly for forced expiratory volume in one second (FEV1) and peak expiratory flow; however, the variety of questions addressed in the included studies did not allow review authors to draw firm conclusions. Information was insufficient for assessment of whether once-daily VI/FF was better or worse than twice-daily FP/SAL in terms of efficacy or safety. It is clear that more research is required to reduce the uncertainties that surround interpretation of these studies. It will be necessary for these findings to be replicated in other work before more robust conclusions are revealed. Only five of the 13 included studies provided data on health-related quality of life, and only six recorded asthma exacerbations. Only one study focused on paediatric patients, so no conclusions can be drawn for the paediatric population. More research is needed, particularly in the primary outcome areas selected for this review, so that we can draw firmer conclusions in the next update of this review.

Plain-language summary: We included 14 studies in this review, involving a total of 6641 participants. All studies lasted between two and 78 weeks. All people included in these studies had received a diagnosis of asthma. Trials included both men and women, and one study included children and young people. All studies looked at VI and FF versus another medication or placebo. In all studies, the VI/FF combination was taken through a dry powder inhaler. We found that participants who received a combination of FF and VI therapy had improved lung function compared with those given placebo, but evidence was insufficient to permit any other conclusions because researchers attempted to answer too many different questions. Evidence was lacking on whether the combination of VI and FF therapy once-daily is better or worse than a twice-daily alternative. More studies are needed, so that we can gain a better understanding of the evidence overall. Overall, the evidence presented in this review is taken from well-designed studies at low risk of bias in terms of decisions on who received which treatment, blinding and how to report outcomes for participants who did not finish the study. However, because we were not able to combine results for many of our outcomes of interest, or because the outcome was rare, we judged the quality of the evidence overall to be low to moderate.