Twenty two trials met the inclusion criteria (n=112,485; range 60 to 39,876): six primary prevention trials (n=95,456) and 16 secondary prevention trials (n=17,029).
In the six primary prevention trials, the rate of serious vascular events was 0.51 per cent per year with aspirin and 0.57 per cent per year without aspirin, representing a statistically significant 12 per cent proportional reduction in occurrence with aspirin (rate ratio 0.88, 95% CI 0.82, 0.94). There was an 18 per cent proportional decrease in the incidence of major coronary events (rate ratio 0.82, 95% CI 0.75, 0.90), but no significant difference in the overall incidence of stroke (rate ratio 0.95, 95% CI 0.85, 1.06). There was no significant effect of aspirin on mortality.
Extracranial bleeding was significantly increased with aspirin (rate ratio 1.54, 95% CI 1.30, 1.82). No statistically significant heterogeneity was observed. The secondary prevention trials showed very similar rate ratios for patients with a history of vascular disease to those found in the primary prevention trials.
Results for a large number of subgroup analyses, including separate analyses for different types of coronary events and stroke, and differences in baseline characteristics, were presented. Hypothetical calculations for five-year predictive effects of aspirin were also presented.