Characteristics of children with invasive pneumococcal disease eligible for the 1+1 compared with the 2+1 PCV13 infant immunisation schedule in England: a prospective national observational surveillance study

Background On Jan 1, 2020, the UK transitioned from a 2+1 to a 1+1 national infant immunisation schedule with the 13-valent pneumococcal conjugate vaccine (PCV13). We assessed whether the 1+1 PCV13 schedule had any impact on incidence, disease characteristics, or outcomes after invasive pneumococcal disease (IPD) in eligible children aged 0-3 years. Methods The UK Health Security Agency conducts IPD surveillance and serotyping of invasive pneumococcal isolates via whole-genome sequencing in England. IPD was defined as identification of Streptococcus pneumoniae in a sterile site. We compared IPD incidence, demographics, clinical presentation, comorbidity prevalence, serotype distribution, and case-fatality rates (CFRs) in children from a single birth cohort eligible for the 1+1 schedule (born between Jan 1, 2020, and Dec 31, 2022) who developed IPD in the 2022-23 financial year (April to March) with children from three equivalent historical birth cohorts (born between Jan 1, 2015, and Dec 31, 2019) eligible for the 2+1 schedule who developed IPD during three respective pre-pandemic financial years: 2017-18, 2018-19, and 2019-20. Findings There were a total of 702 IPD episodes in 697 children, including 158 (incidence 8<middle dot>99 per 100 000 person- years) in the single 1+1 birth cohort and 544 (incidence 9<middle dot>39 per 100 000 person-years) in the 2+1 birth cohorts, with no significant difference in the incidence of overall IPD (incidence rate ratio 0<middle dot>96, 95% CI 0<middle dot>80-1<middle dot>14, p=0<middle dot>63), PCV13-type IPD (1<middle dot>21, 0<middle dot>71-2<middle dot>00, p=0<middle dot>45), or pneumococcal meningitis (0<middle dot>97, 0<middle dot>66-1<middle dot>40, p=0<middle dot>88). Comorbidity prevalence, clinical presentation, and CFRs were also similar between the two cohorts, as was the percentage of cases in infants too young to be vaccinated (<2 months old) and infants aged 5-11 months who received one or two PCV13 priming doses, in the 1+1 and 2+1 cohorts respectively. Interpretation After 3 years, the 1+1 schedule continues to provide direct and indirect protection against PCV13-type IPD in children, with no significant change in overall IPD incidence, serotype distribution, clinical presentation, or CFRs in children eligible for the 1+1 compared with the 2+1 schedule. Ongoing surveillance will be important to assess longer-term direct and indirect population protection.