[sabat]

It's not limitless, but scientific testing has shown it can handle much more than you are imagining.

I'm not sure how the immunity conferred by the vaccine differs from that conferred by the live virus. It is probably just as good, but what if it isn't?

It doesn't differ at all. All vaccines are made of live-but-weakened or dead versions of viruses. Your immune system doesn't realize that, and reacts as though it's being attacked. The "hard" part for it is concocting antibodies for the virus it's discovered. And that, naturally, is the beneficial effect of the vaccine, because the immune system doesn't easily forget how to make that kind of antibody. Vaccines work because the immune system reacts the same way to a weak or dead virus that it does to a live, strong one.

[mbreese]

You don't know what I'm imagining. I think that a load of approx. 3 different antigens per inoculation with a buffer of at least 6-12 weeks in between them is adequate for coverage of most vaccines. All I was saying is that the current regiment of spread out vaccines is done for a reason. The original (parent/parent/...) poster said that it was done "to be safe". My point is that it is done that way for more than one reason... chief among them efficacy. You want the antibodies that you create to last.

I know the way vaccines work.

The part that you don't get with a stock vaccine is immunity when dealing with new strains or mutations that aren't accounted for by the stock vaccine. The antigenic make up of the new strain may be different. This is why we get different flu shots every year. With something as simple as chicken pox, I don't think that there are many strains (I could only find 2 while quickly Googling), so one shot and you're covered.

But in the case of something like H1N1, someone may get the vaccine and assume they are covered. They then may get lax about standard precautions, thinking that they are covered. And then when a new strain rolls around, you're susceptible.