> what is different between the vaccines?
The shingles vaccine is a larger/more aggressive dose than the chickenpox vaccine.
And nowadays chickenpox vaccine uses live attenuated viruses (i.e. modified to be non-infectious but still look the same) whereas the shingles vaccine uses recombinant proteins. This allows the shingles vaccine to deliver the higher viral load that they want for inoculating against shingles without putting a bunch of live viruses into the body.
It's also worth noting that the recombinant vaccine is more effective for shingles compared to the equivalent viral load live vaccine by a significant margin. It's something like 90% reduction in incidence vs 50%.
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> How it presents shouldn't matter as much?
It's not an all or nothing thing but it's a matter of percentages.
And the big reason why they present differently is that chickenpox kind of attacks every part of the body since it's new. It of course does best at infecting the skin and nerves but it mildly affects every part of the body. But then it goes dormant in the nerves because that's where it's most "compatible" and the body is the worst at fighting it.
So then with shingles your body still has the immunity but the reactivated virus is able to out-compete your immunity in the nerves and it wakes up in whatever specific nerve and spreads along that nerve. This is why shingles generally presents in a band on the body. It's spreading along a specific nerve "line" rather than spreading throughout the whole body, blood, and all.
And so the because the infection can't spread broadly throughout your body it ends up concentrated in that location and presumably the higher viral load combined with focusing on the specific proteins rather than the whole virus increases the body's sensitivity to these flair ups, catching them before they can reach momentum. And then that focused immune training sits on top of the body's existing immunity for the initial "whole body" presentation of the virus.