Carriage of pneumococci after pneumococcal vaccination. 1996, Obaro, Lancet

Because the invasion requires bacterial colonization in the nasopharynx to begin with, the goal of vaccination is also to reduce the colonization of pneumococcus. For the first time, conjugated pneumococcal vaccine was tested in infants in the Gambia in 1993, where it was found that while colonization with vaccine serotypes decreased by 78% -89%, colonization by non-vaccine serotypes increased 4.5-fold.