Characteristics of Invasive Pneumococcal Diseases Cases Among U.S. Children With Hematologic Malignancies Before and After Introduction of Thirteen-valent Pneumococcal Conjugate Vaccine, 2005-2019.

Background: Children with hematologic malignancies (HMs) are at increased risk of invasive pneumococcal disease (IPD). Data on long-term IPD trends in U.S. children with HM after 13-valent pneumococcal conjugate vaccine (PCV13) introduction are limited. We assessed IPD trends in children with HM before and after PCV13 introduction and the proportion of IPD cases caused by serotypes contained in new pneumococcal conjugate vaccines (PCV15 and PCV20, introduced after 2019).

Methods: During 2005-2019, IPD cases among children aged <18 years were identified through the Active Bacterial Core surveillance. We characterized IPD cases by underlying conditions (HM, other IPD risk factors, no IPD risk factors) and time periods [pre-PCV13 (2005-2009), early-PCV13 (2010-2014) and late-PCV13 (2015-2019)]. We estimated incidence rate ratios (IRRs) in children aged <5 years with and without HM and during 2010-2019.

Results: We identified 5912 cases of IPD in children aged <18 years; 215 (3.6%) were among children with HM. The proportion of IPD cases with PCV13 serotypes decreased over time in all risk groups; however, IRRs among children with vs. without HM were 215.8 [95% confidence interval (CI): 146.1-292.4] and 240.9 (95 CI: 152.3-341.1) in early and late-PCV13 periods, respectively. In late-PCV13 period, PCV15/non-PCV13 serotypes and PCV20/non-PCV15 serotypes caused 19.4% and 4.8% of IPD cases among children with HM.

Conclusions: The proportion of PCV13-type IPD decreased in all children after PCV13 introduction. However, children with HM remain at an increased risk of IPD. Continued monitoring of the impact of PCV15 and PCV20 use among children with HM is needed.