Invasive pneumococcal disease in UK children under 1 year of age in the post-PCV13 era: what are the risks now?

Background. Invasive pneumococcal disease (IPD) has declined significantly since the introduction of pneumococcal conjugate vaccines (PCVs). It is not known whether certain infant populations remain at higher risk of IPD in countries with established 13-valent PCV (PCV13) programs. We aimed to describe the epidemiology, clinical characteristics, serotype distribution, and outcomes of IPD in infants, and to estimate the relative risk of PCV13-type, non-PCV13-type, and overall IPD in premature infants compared to term infants during a 4-year period after the PCV13 program was established. Methods. This was a prospective, enhanced national surveillance of laboratory-confirmed IPD in England in infants aged <1 year diagnosed during 2013-2016. Results. There were 517 cases of IPD (incidence: 19/100 000 infants). Incidence was significantly higher in premature infants compared with those born at term (49/100 000 vs 17/100 000; incidence rate ratio [IRR], 2.87; P < .001), with infants born before 28 weeks' gestation having the highest incidence (150/100 000; IRR, 8.8; P < .001). Of the 454 IPD cases with serotyped isolates, most were caused by non-PCV13 serotypes (369 cases, 71.4%), with 85 cases (16.4%) due to PCV13 serotypes. There were 31 deaths (case fatality rate [CFR], 6.2% [95% confidence interval, 4.3%-8.6%]). Premature infants did not have a higher CFR than term infants (P = .62). Conclusions. IPD incidence in infants remains lower than rates reported prior to PCV7 introduction in England. The risk of IPD remains significantly higher in premature infants compared to infants born at term, for both PCV13 and non-PCV13 serotypes. Any changes to the infant PCV13 immunization schedule may disproportionally affect premature infants.