There seems to be some misinformation being spread about this. Please read the advice from Beverley Hunt, professor of thrombosis and haemostasis at King’s College London and a representative of Thrombosis UK.
"There has been no advice that anyone should take medication to prevent rare clotting events. Hunt cautioned against taking aspirin, stressing it is thought the clotting problems are down to an immune response.
“So taking aspirin is not going to be helpful. Taking an anticoagulant probably isn’t going to be helpful, especially if you are going to get a low platelet count, it will increase your risk of bleeding,” she said. “And we know if you take aspirin and you don’t need to take aspirin the benefits aren’t very good and there is a risk that you can bleed spontaneously.”"
www.theguardian.com/world/2021/apr/07/what-do-i-need-to-know-about-the-oxfordastrazeneca-vaccine
Also bear in mind that in the UK aspirin is thought to contribute to around 3000 deaths per year and 20,000 bleeds.
www.theguardian.com/science/2017/jun/14/risk-of-bleeds-and-death-with-daily-aspirin-use-higher-than-thought