Finally, the development of conjugated vaccines, such as those based
on encapsulated H. influenzae type b and pneumococcus, can diminish
bacterial disease and the consequent need for antibiotics. But vaccine
development and delivery are problematic. In addition, with the transformation
of commensal strains into pathogens in immunocompromised
individuals, the activity of vaccines against these organisms could
paradoxically destroy a natural defense against recognized pathogens.