I don't have any empirical evidence about this. However, I do know that activation of the immune system is costly to an individual organism. It uses energy, a

I don't have any empirical evidence about this. However, I do know that activation of the immune system is costly to an individual organism. It uses energy, and this can lead to sub-optimal functioning of other systems. I do not know if giving multiple vaccines at once means that activation of the immune system is greater, but it would seem logical that a larger number of foreign particles in the bloodstream would do that.