Vaccines Always Work. True or False

Vaccines always work. True or false?

A) False. Sometimes memory cells are not produced.
B) True. They always work to some degree.
C) False. Some pathogens change so fast that memory cells for an earlier infection won't recognize the same pathogen in a subsequent infection.
D) True. We've eliminated many diseases using them.
E) False. Sometimes scientists don't make them correctly.