Three escapes, one idea: a capsule hides you from phagocytes, antigenic variation hides you from antibodies, and going intracellular hides you inside the very cell antibodies can't follow you into.
Watch for overwhelming or reactivated infection. Encapsulated microbes (pneumococcus, meningococcus, Hib) can overwhelm asplenic and sickle-cell patients — vaccinate them. Intracellular hiders like M. tuberculosis stay latent for years and reactivate under steroids, TNF-inhibitors, or HIV.