Following on from another thread, I am wondering if any vaccines provide life long immunity. I had assumed most did until the recent whooping cough epidemic. I understand influenza does not, for example, as it mutates every year.
Immunity -whether natural or vaccine acquired - depends on a) the pathogen staying the same (as you have mentioned above this is why people catch flu more than once) and b) 'boosters'. In - for example - the 60's/70's you would have had - for example - measles (or a measles vaccine I guess) developing immunity. Then a few years later you would come into contact with measles again and this would have boosted your measles immunity and so on and so forth. Now measles has been pretty much removed from circulation no-one with measles immunity (whether vaccine or naturally acquired) will be getting boosters so we might expect to see both types of immunity to decrease over the years. Naturally acquired immunity tends to last longer than vaccine acquired but will still fade without boosters from exposure. Of course at some stage this could lead to a significant outbreak which presumably will result in a later vaccine booster being added to the schedule. Measles immunity does seem to last pretty well, so you might see this sort of thing happening with some of the other vaccine preventable diseases first. Hib maybe as it used to be common for most to be immune by age 5 so there was obviously quite a lot that used to circulate (and it's already had to be changed once as immunity didn't last as long as expected).
So slightly unnervingly for many, if you have a vaccinated child, and the vaccine has worked, then the very best thing for your child is to actually be exposed to the diseases they have been vaccinated against as this will give their immunity a natural boost. Please note I am NOT suggesting you expose your child on purpose, because of course you have no way of knowing whether the vaccination has worked or not in your child.
Sorry that's a bot confusing as I'm using 'booster' to mean naturally acquired boosters from disease, and vaccine boosters.
The key concept is if you remove a disease from circulation then you stop repeated exposures. In the past those repeated exposures would have topped up the immunity and so immunity tended to be lifelong. Now without repeated exposures to circulating disease immunity is more likely to wane. Vaccine immunity is expected to wane faster than naturally acquired, but naturally acquired will still wane without further exposure to circulating disease (or a vaccine booster obviously).
Here's a list of how long immunity lasts. As you can see, most are pretty good.
Waning immunity is an important consideration in deciding the timing of vaccinations. The schedules are set so as immunity is at it's highest when vulnerability is highest. As such, people who delay vaccinations get less benefit from them.