Dynamics of invasive pneumococcal disease in infants < 2 years old following PCV7/13 implementation using two infant and a booster dose schedule: evidence for indirect protection of young infants, Israel, 2004 to 2019

Background: Pneumococcal conjugated vaccine (PCV)7 and PCV13 programmes started in Israel from July 2009 and November 2010 respectively, with a 2+1 schedule (one dose at 2monthsold, one at 4monthsold, and a booster dose at 12monthsold). Thereafter, invasive pneumococcal disease (IPD) rates substantially declined in children. Uptake of all three doses in <2-year-olds since 2012 is >90%. For still incompletely vaccinated infants (≤12monthsold), how well the PCV 2+1 programme shields from IPD is not fully resolved. Aim: To assess the adequacy of protection conferred by the 2+1 schedule PCV vaccination programme, particularly among incompletely-vaccinated infants. Methods: This was a population-based, prospective, nationwide active IPD surveillance study in Israel, 2004–2019, in children <24monthsold. We estimated annual incidence rates (IR) of overall IPD, IPD caused by PCV13 serotypes (VT13), and non-PCV13 serotypes (NVT13). Annual IPD IRs were stratified by age: <4months (receiving ≤1dose), 4–6months (immediately post dose2), 7–12months (a few months post dose2), and 13–23months (post dose3). Late-PCV (2004–2008) to pre-PCV13 (2016–2019) mean annual IR ratios (IRRs) were calculated. Results: 2,569 IPD episodes were recorded. VT13 decreased >90% in all age groups, while NVT13 seemed to increase. All-IPD rates declined in all age groups by 56–70%. The 2+1 schedule impact on 7–12-month-old infants (pre-booster) was similar to that on 13–23-month-old children (post booster), with PCV13 IPD reductions of 97% and 98%, respectively. Conclusions: Indirect (herd) protection of infants, including <4month-olds with ≤1PCVdose, was achieved by the 2+1 PCV schedule programme which thus seems adequate.