Conclusions. The majority of deaths in the 1918–1919 influenza pandemic likely resulted directly from secondary bacterial pneumonia caused by common upper respiratory–tract bacteria. Less substantial data from the subsequent 1957 and 1968 pandemics are consistent with these findings...
This is the conclusion from a 2008 study by no less an interested party than Fauci. You can find the full study embedded below and/or it can be downloaded from here or read in the google PDF reader here.
Such an indication might be a reminder for those absolutely needing/required to wear (non-disposable) face masks/face coverings, as to how vital it is for them to be kept scrupulously clean at all times, in addition to them not being worn at all while suffering/recuperating from influenza. Naturally, it has always been standard practice that those suffering influenza keep themselves to themselves as much as possible. Infact the bottom row of table 3 in the study reads:
The near universal observation that strict bed rest early in the course of uncomplicated influenza prevented pneumonia and death is consistent with an effect of isolation from carriers of bacterial pathogens
Further, the conclusion goes on to stress the importance of the availability of antibiotics for the treatment of bacterial pneumonia:
If severe pandemic influenza is largely a problem of viral-bacterial copathogenesis, pandemic planning needs to go beyond addressing the viral cause alone (e.g., influenza vaccines and antiviral drugs). Prevention, diagnosis, prophylaxis, and treatment of secondary bacterial pneumonia, as well as stockpiling of antibiotics and bacterial vaccines, should also be high priorities for pandemic planning.
and:
suggests that early and aggressive treatment, including antibiotics and intensive care, could save most patients [84, 85] and also underscores the importance of prevention and prophylaxis.
and:
The present work leads us to conclude that in addition to these critical efforts, prevention, diagnosis, prophylaxis, and treatment of bacterial pneumonia, as well as the stockpiling of antibiotics and bacterial vaccines [84, 85, 93], should be among the highest priorities in pandemic planning. We are encouraged that such considerations are already being discussed and implemented by the agencies and individuals responsible for such plans [94, 95].