No doubt secondary infections were part of Swine flu mortality in 1918-1919 flu epidemic.
What I’m trying to explain is that it was a stronger strain than the current one, and that it killed a number of people outright before they could have developed secondary infections.
Not only secondary infections but it is now being researched that administering Aspirin may have contributed as well by way of pulmonary edema, an abnormal build up of fluid in your lungs that can be caused by taking too much aspirin.
There wasn’t a whole lot to offer back then by way of treatment.