Get the measles vaccine, and you won’t get the measles—or give it to anyone else. Right? Well, not always. A person fully vaccinated against measles has contracted the disease and passed it on to others. The startling case study contradicts received wisdom about the vaccine and suggests that a recent swell of measles outbreaks in developed nations could mean more illnesses even among the vaccinated.
Yep, this is a good thing for people to know (Especially with regards to flu). Infectious disease is always an arms race and while "prepare the immune system" is a pretty good gun, there is always the counter of "look like something else".
New strains are always a possibility, but from the point of view of the herd, it's best to promote whatever guns have the best chance of wiping out the bugger before it mutates and targeting so their aim is true. This holds true for vaccines, but also antibiotics, antivirals, antifugals, etc.
(Ignoring all discussion of vaccine lifetime and the chance a vaccine goes bad before delivery)