Well, since flu is caused by a virus, and a majority of pneumonias are caused by bacteria (usually Streptococcus pneumoniae species), you shouldn't expect the flu shot to have any protective effect against pneumonia. The body has a totally different subset of immune cells that combat viruses versus those that combat bacterial infections. Still, if your mother's pneumonia was caused by a virus, the flu shot wouldn't be expected to have any specific protection even against viral pneumonia. If she came down with the flu after getting the shot, there's some real cause for chagrin...Sorry to hear about you mother, did she recover well?