That is an excellent question, I hope someone studies this in the future. The best I can offer is this study on flu vaccines that seem to show that annual repeated uptake undermine CD4 cell response;"We find a striking disparity in their responses, with previously vaccinated subjects exhibiting significantly blunted CD4 T-cell responses and diminished antibody responses." (1) I know they are different viruses etc, but it is something to consider in light of the previous mentioned study and also all what seems to be going on with CDC.