Do you understand that the immune system will identify anything as foreign and mount an immune response.
Do you understand that anaphlotoxins are released by pathogens which enable chemotaxis of antigen presenting cells like macrophages, dendritic cells and B cells. Which phagocytose the pathogen or part of it and then present these parts to other cells in the immune system.
For instance a macrophage will scavenge a pathogen and then present it on its MHC type 1 marker. It will then migrate to a lymph node and present it to the relevant B or T cell. The presentation process triggers the release of cytokines, a cocktail of chemicals, which causes the division of the B cell in this case, which then divides and differentiates into both memory cells and plasma cells.
If you understood more you wouldn't ask the question "why so many disease outbreaks in vaccinated populations" because you would appreciate the nonsense of that statement.
A person may have a recurrence of an infection where their immune system is compromised eg) stress, immunosuppressive drugs etc
