Emerging evidence is that excessive aspirin at the time of the Spanish Flu (and over dosing) may have killed many. Not just the bacterial pneumonia and no antibiotics then, but the misuse of aspirin.

Start here:

‘Antiplatelet/anticoagulant effects of NK Low-dose aspirin (85-100mg daily), as a potent anticoagulant agent, is widely used for the prevention of heart attacks, stroke, and atherothrombotic diseases.

Aspirin exerts its antiplatelet action by inhibiting cyclooxygenase (COX) and subsequently reducing the synthesis of thrombogenic thromboxane A2 (TXA2) in platelets. However, the long-term use of aspirin comes with serious gastrointestinal (GI) side effects and bleeding.49