Effectiveness of influenza vaccination in reducing influenza-like illness and related antibiotic prescriptions in adults from a primary care-based case-control study

•Influenza vaccination reduced primary care presentations for ILI.•The pooled estimated reduction over 4 years was 24% (95%CI 11-34%).•Influenza vaccination also reduced antibiotic prescribing for ILI.•However, this was only observed in patients without comorbidities and aged 40-65yrs. Evidence on the effectiveness of influenza vaccine in preventing antibiotic prescriptions for influenza-like illness (ILI) in adults is limited. A primary care-based case-control study was conducted to estimate influenza vaccine effectiveness (VE) against influenza-like illness (ILI) and antibiotic prescribing for ILI in adults aged ≥40 years. Cases were patients diagnosed with ILI from 1st June to 30th September in each year, 2015-2018; a subset of those with ILI prescribed antibiotics was also defined. Controls were patients attending a practice who did not receive an ILI diagnosis. Generalised estimating equations were used to calculate adjusted VE overall, by age (