Emergence of Nonvaccine Serotypes following Introduction of Pneumococcal Conjugate Vaccine: Cause and Effect?

Since the 7valent pneumococcal conjugate vaccine (PCV7) was first introduced in the United States in 2000, there has been great interest in understanding its clinical and public health impact. Early reports after the introduction of PCV7 revealed striking reductions in the incidence of invasive pneumococcal disease (IPD) throughout the United States, not only among the population targeted for vaccination, but also among persons too young or too old to receive the vaccine [1-3]. These changes were so dramatic that long-standing disparities in the incidence of IPD among certain racial and ethnic groups were substantially reduced [4, 5]. The incidence of more-common manifestations of pneumococcal disease, such as otitis media [6] and hospitalizations for pneumonia [7], has also decreased, providing evidence of a much broader public health impact. Epidemiological studies have shown the vaccine to