Abstract Aims To evaluate whether a strategy of double-dose influenza vaccination during hospitalization for an acute coronary syndrome (ACS) compared with standard-dose outpatient vaccination (as recommended by current guidelines) would further reduce the risk of major cardiopulmonary events. Methods and results Vaccination against Influenza to Prevent cardiovascular events after Acute Coronary Syndromes (VIP-ACS) was a pragmatic, randomized, multicentre, active-comparator, open-label trial with blinded outcome adjudication comparing two strategies of influenza vaccination following an ACS: double-dose quadrivalent inactivated vaccine before hospital discharge vs. standard-dose quadrivalent inactivated vaccine administered in the outpatient setting 30 days after randomization. The primary outcome was a hierarchical composite of all-cause death, myocardial infarction, stroke, unstable angina, hospitalization for heart failure, urgent coronary revascularization, and hospitalization for respiratory causes, analysed by the win ratio method. Patients were followed for 12 months. During two influenza seasons, 1801 participants were included at 25 centres in Brazil. The primary outcome was not different between groups, with 12.7% wins in-hospital double-dose vaccine group and 12.3% wins in the standard-dose vaccine group {win ratio: 1.02 [95% confidence interval (CI): 0.79–1.32], P = 0.84}. Results were consistent for the key secondary outcome, a hierarchical composite of cardiovascular death, myocardial infarction and stroke [win ratio: 0.94 (95% CI: 0.66–1.33), P = 0.72]. Time-to-first event analysis for the primary outcome showed results similar to those of the main analysis [hazard ratio 0.97 (95% CI: 0.75–1.24), P = 0.79]. Adverse events were infrequent and did not differ between groups. Conclusion Among patients hospitalized with an ACS, double-dose influenza vaccination before discharge did not reduce cardiopulmonary outcomes compared with standard-dose vaccination in the outpatient setting. Clinical Trial Registration ClinicalTrials.gov number: NCT04001504