Suspected and unexpected clinical features of pathogens might only become apparent during clinical trials to test vaccines or after implementation of vaccination programmes. For example, the role of Haemophilus influenzae type b (Hib) in early childhood pneumonia was not evident until findings of a clinical vaccine trial in The Gambia showed that—after 3 years of follow-up—Hib caused more than 20% of radiologically defined pneumonia in infants. Moreover, the ability of different pneumococcal serotypes, but not meningococcal serogroups, to replace competing strains in nasopharyngeal carriage and invasive disease was only noted after implementation of pneumococcal and group C meningococcal glycoconjugate vaccines.

Introduction of oral, live-attenuated rotavirus vaccines—namely, the pentavalent vaccine RotaTeq (RV5; Merck, Whitehouse Station, NJ, USA) and the monovalent vaccine Rotarix (RV1; GlaxoSmithKline Biologicals, Rixensart, Belgium)—to many developed and developing settings offers the potentia