Along with the circumstances of WWI and lack of hygene, that flu pandemic will not be repeated in 2009.
If you read even a simple Wikipedia or a much deeper medical explanation on that pandemic, yes, secondary infections did cause deaths. Not all for sure but many.
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.