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Abstract
Background: Population impact of pneumococcal conjugate vaccines (PCV) depend on direct and indirect protection. Following Malawi’s 2011 introduction of the 13-valent PCV (PCV13), we examined impact on vaccine serotype (VT) and non-VT (NVT) invasive pneumococcal disease (IPD) among vaccine-age-eligible and vaccine-age-ineligible children and adults. Methods: Laboratory-based surveillance at a government hospital in Malawi included 6 years before and 7 years after PCV13 introduction. Using negative-binomial regression, we evaluated secular trend-adjusted Incidence Rate Ratio (IRR) in VT- and NVT-IPD prior to and post PCV introduction. We compared predicted counterfactual incidence in hypothetical absence of vaccine with empirically observed incidence following vaccine introduction. A case-control study assessed vaccine effectiveness compared PCV uptake among vaccine-age-eligible IPD cases versus matched community controls. Findings: Surveillance covered 10 281 476 person-years observation, with 140 498 blood and 63 291 cerebrospinal fluid cultures. IPD decline preceded PCV introduction. Compared to the counterfactually predicted incidence, post-vaccine VT-IPD incidence was 38% (95%CI: 37, 40) lower among infants, 74% (70, 78) among young children, 79% (76, 83) among older children and 47% (44, 51) among adolescents and adults. Though NVT-IPD has increased since 2015 , absolute rates remain low. The case-control study, (19 cases and 76 controls), showed vaccine effectiveness against VT-IPD of 80·7% (-73·7, 97·9). Interpretation: Even with pre-existing declines, infant PCV13 introduction has led to substantial IPD reduction among vaccine-age-eligible children. However, seven years after PCV introduction, indirect effects benefitting unvaccinated infants and adults were more modest. Policy decisions should consider alternative strategies, including targeted vaccination outside infant EP to benefit vulnerable populations. Funding Statement: This work was funded by Bill & Melinda Gates Foundation, USA (OPP117653) to RSH and a Wellcome Trust Programme Grant (WT091909/B/10/Z) to NF, NAC, RSH; National Institute for Health Research (NIHR) Global Health Research Unit on Mucosal Pathogens using UK aid from the UK Government (Project number 16/136/46) to RSH. The MLW Clinical Research Programme is supported by a Strategic Award from the Wellcome Trust, UK (206545/Z/17/Z) to SG. Declaration of Interests: NBZ, NAC & NF have received investigator-initiated research grants from GlaxoSmithKline Biologicals. NBZ & NAC received investigator-initiated research grants from Takeda Pharmaceuticals. NAC has received research grant support and honoraria for participation in rotavirus vaccine advisory board meetings from GlaxoSmithKline Biologicals. All other authors declare no competing interests. Ethics Approval Statement: The study protocol was approved by Malawi’s National Health Sciences Research Committee (NHSRC; protocol 867), by the University of Malawi College of Medicine Research and Ethics Committee (COMREC; P.01/08/609 and P.09/09/826) and the University of Liverpool Research Ethics Committee (UoLREC; RETH490). The Centers for Disease Control and Prevention relied on the UoLREC for ethical approval. For the case-control component, the parent/guardian of all child participants provided written informed consent and, in addition, children 8 years or older provided written informed assent. This included consent for publication.
Highlights
Streptococcus pneumoniae is estimated to be responsible for more than 318 000 deaths per year in children aged 1–59 months worldwide, with the highest mortality burden in Africa.[1]S pneumoniae has almost 100 serotypes and is a common coloniser of the human nasopharynx, in young children and resource-poor and HIV-affected populations.[2]
This study showed a direct reduction in the incidence of invasive pneumococcal disease among children following introduction of PCV13, accelerating the pre-existing reductions in incidence
In Malawi, we have demonstrated the early onset of pneumococcal colonisation,[19] a high prevalence of residual vaccine serotype carriage among children since introduction of PCV13 in 2011,4 and persistent high prevalence of pneumococcal carriage among HIVinfected adults receiving antiretroviral therapy.[20,21]
Summary
Streptococcus pneumoniae is estimated to be responsible for more than 318 000 deaths per year (uncertainty ratio 207 000–395 000) in children aged 1–59 months worldwide, with the highest mortality burden in Africa.[1]S pneumoniae has almost 100 serotypes and is a common coloniser of the human nasopharynx, in young children and resource-poor and HIV-affected populations.[2]. Laboratory Service, Johannesburg, South Africa (Prof A von Gottberg PhD); School of Pathology, University of the Witwatersrand, Johannesburg, South Africa (Prof A von Gottberg); National Center for Immunization and Respiratory Diseases, Centers for Disease Control & Prevention, Atlanta, GA, USA (J R Verani MD, C G Whitney MD); Ministry of Health, Lilongwe, Malawi (C Mwansambo FRCPCH); Liverpool School of Tropical Medicine, Liverpool, UK (Prof S B Gordon).
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