 Methods. Population: 4400 patients with ST-elevation STEMI or non-ST elevation myocardial infarction NSTEMI are randomized 1:1 in a blinded fashion using an RRCT design and followed up via registries and two telephone calls. Intervention: Influenza vaccination. Control: Placebo saline. Outcome: The primary endpoint is a composite of death, myocardial infarction and stent thrombosis till 1 year in patients with STEMINSTEMI undergoing coronary angiographyPCI. Patients will be included in the study in all of Swedens 7 university hospitals and 2 general hospitals, 4 university hospitals and 1 general hospital in Denmark, in 1 specialized heart center in Norway, 3 university hospitals in Czech Republic, 5 hospitals in Scotland and 1 university hospital in Latvia. Secondary endpoints are time to all-cause death, time to stent thrombosis, time to revascularization, time to myocardial infarction, time to stroke or time to rehospitalization for heart failure till 1 year, 2 years, 3 years and 5 years. Furthermore, an extensive health-economic analysis will be conducted. The trial has been approved by the ethical committee system Dnr 2014264 and the Medical Products Agency EudraCTnr -2014-001354-42 in Sweden. 