Even natural immunity isn't lifelong for some people, but vaccines really only last five to ten years (cf., e.g., tetanus), and should continue being boosted into adulthood. It's just not a requirement so it doesn't tend to happen unless you work with an at-risk population.
I got a single unboosted mumps vaccine in 1985 or so and have been exposed multiple times since then and still haven't gotten mumps, whereas in the recent Midwest mumps epidemic, about 65% of those who came down with it had been vaccinated, and many had been either vaccinated or boosted within the previous six years.
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Date: 2010-11-24 08:38 pm (UTC)I got a single unboosted mumps vaccine in 1985 or so and have been exposed multiple times since then and still haven't gotten mumps, whereas in the recent Midwest mumps epidemic, about 65% of those who came down with it had been vaccinated, and many had been either vaccinated or boosted within the previous six years.