You may not always be infected with a resistant strain.
Someone else will be.
How do you think we got MRSA?
The current pertussis vaccine escape mutant has a mortality/morbity about 10X greater than the original strain. And the vaccine has zero effectiveness against it.
Try for a 100X strain?
But wait!, there’s more!
http://www.scientificamerican.com/article/baboon-study-reveals-new-shortcoming-of-pertussis-vaccine/
Thanks for your question.
MRSA and many other type of antibiotic restistance are plasmid mediated, the genes encoding these enzymes are easily transferable among different bacteria from different species of bacteria.
You may read this http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4216585/