Background. Streptococcus pneumoniae is an uncommon but well-recognized cause of invasive bacterial disease in young infants. This study aimed to determine the impact of the 7-valent pneumococcal conjugate vaccine (PCV7) on invasive pneumococcal disease (IPD) in infants aged <90 days in England and Wales and describe their clinical characteristics following PCV7 introduction.

Methods. Trends in IPD among infants aged <90 days during 1998–1999 through 2009–2010 were analyzed using enhanced national surveillance data. Following PCV7 introduction, clinical information was also obtained for IPD cases in the birth cohorts eligible for vaccination.

Results. Prior to PCV7 introduction, IPD incidence in infants aged <90 days was 13.0 (95% confidence interval [CI], 12.0–14.0) per 100 000 live births and PCV7 serotypes accounted for 44% (154/349) of serotyped isolates. PCV7 introduction resulted in 83% (95% CI, 66%–91%, P < .001) reduction in PCV7 IPD and a declining trend in overall IPD by 2009–2010. Of the 256 cases diagnosed after PCV7 introduction, 23% (n = 60) had been born before 37 weeks’ gestation. A third of cases (84/256, 33%) developed IPD in the first 48 hours of life, where 42% (35/84) were premature. Meningitis was diagnosed in 94 infants (37%) and its prevalence increased with age. Case fatality was 7% (18/256) and was higher for meningitis than nonmeningitis cases (adjusted odds ratio, 3.8 [95% CI, 1.2–12.0], P = .024).

Conclusions. Young infants have benefited from PCV7 through indirect (herd) protection. Given that a third of cases occurred within 48 hours of birth, further studies should focus on risk factors for IPD in pregnancy and strategies to prevent mother-to-child transmission.