Sustained impact of 10-valent pneumococcal conjugate vaccine on invasive pneumococcal disease in Kenya, 2011-2022
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Background
There are only a few long-term PCV impact assessments in sub-Saharan Africa, and these have been confined to settings using a 13-valent PCV. A 10-valent PCV was introduced in Kenya in 2011 with catchup vaccination among children aged <5 years in Kilifi. We evaluated the impact of PCV10 introduction in Kilifi through 2022.
Methods
Surveillance for IPD among residents of the Kilifi Health and Demographic Surveillance System was conducted at the Kilifi County Referral Hospital. Identification of pneumococcus isolated from blood or cerebrospinal fluid and pneumococcal serotyping were conducted according to WHO recommendations. Age– and serotype-specific incidence rate ratios, adjusted for pre-defined confounders (aIRRs), were used to compare annual IPD incidence in the pre-vaccine period to that in 2017-2019 (late post-vaccine) and 2020-2022 (COVID-19).
Findings
Compared to the pre-vaccine period, the incidence of vaccine serotype (VT) IPD among children aged <5 years was significantly lower in 2017-2019 (aIRR 0.14; 95%CI 0.04-0.49) and in 2020-2022 (aIRR 0.03; 95%CI 0.00-0.25). It also declined among older children and adults. The incidence of non-VT (NVT) IPD among children aged <15 years was higher during the post-vaccine period. All serotype IPD incidence declined across all age groups. Among individuals with NVT-IPD, serotypes included in new-generation PCVs accounted for about one-third and about one-half of disease among individuals aged <5 years and ≥5 years, respectively.
Interpretation
Despite potential waning of the effects of catchup vaccination during introduction, reductions in VT-IPD incidence were sustained through 12 years of PCV10 use. All serotype IPD incidence declined across all ages despite serotype replacement among children. New-generation PCVs may enhance IPD control.
