A Pain in the Ear: What Has the 7-Valent Conjugated Pneumococcal Vaccine Done to Reduce the Incidence of Acute Otitis Media?

would not be large; only 20%–30% of cases of AOM in the United States are associated with middle ear specimens that grow S. pneumoniae on culture [2]. Approximately 70% of children with S. pneumoniae–related AOM had S. pneumoniae serotypes contained in or closely related to serotypes contained in PCV7 [3]. At best, then, we expected an overall risk reduction of ∼20% for AOM among US children who completed the PCV7 vaccination course. Among 37,868 infants randomly assigned to receive either PCV7 or meningococcus type C conjugate vaccine in California, those receiving PCV7 experienced a 7.8% relative risk reduction in clinically diagnosed cases of AOM (95% CI, 5.2%–10.5%), and a 20% relative risk reduction in the placement of ventilatory tubes (95% CI, 3.6%–34.1%) [4]. Investigators in Finland found a 6% relative risk reduction in AOM among 831 infants receiving PCV7, compared with 831 receiving hepatitis B vaccine [5]. The 95% CI for the protective efficacy of the vaccine against AOM in this study was 4% to 16%. This has been interpreted as an indication that vaccine use might actually increase the frequency of AOM. This has some biological plausibility, because the increase in the incidence of AOM attributable to S. pneumoniae serotypes or to other otopathogens not contained in the vaccine might be greater than the decrease in the incidence of AOM attributable to S. pneumoniae serotypes contained in PCV7. Thus, these non-PCV7 serotypes would substitute for the eliminated vaccine strains and produce the same or greater incidence of AOM. More likely, the large 95% CI in the Finnish study was directly due to the small sample size, combined with the modest size of the relative risk reduction for AOM attributable to immunization with PCV7 [5]. In the California study, the large sample size narrowed the 95% CI and showed a 97% probability that the relative risk reduction was 5.2% [4].