Multi-pathogen serosurveillance of vaccine preventable and neglected tropical diseases in Samoa 2018-2024 to inform public health action
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Background
Serosurveillance can estimate the prevalence of antibodies (Ab) acquired through vaccination or current and/or past infection. Multi-pathogen serosurveillance that measures multiple Ab simultaneously, can enable identification of vulnerable sub-populations with immunity gaps to vaccine preventable diseases (VPD) and concurrent burden of neglected tropical disease (NTD), including those nearing elimination (lymphatic filariasis [LF], trachoma) and eradication (yaws). This study aimed to estimate seroprevalence and identify temporal trends of selected VPDs and NTDs in Samoa to inform targeted public health action.
Methodology/Principal Findings
Dried blood spots were collected from four repeated community-based surveys in eight primary sampling units (PSU) in Samoa in 2018, 2019, 2023 and 2024. Multiplex bead assays were used to detect Abs against antigens (Ag) for diphtheria, measles, rubella, tetanus, LF [ Wb123 or Bm14 ], yaws [both Rp17 and TmpA; <14 years only], and trachoma [Pgp3; <14 years only]. Seroprevalence estimates were adjusted for sampling design and standardised for age and sex. Overall, 2,871 participants were included in this analysis. Seroprevalence of measles increased from 42% in 2018 to 95% in 2024, whereas diphtheria decreased from 79% in 2018 to 65% in 2024. Seroprevalence to yaws remained <1% for all years, whereas trachoma decreased from 21% to 7% (2018–2024). LF seroprevalence decreased between 2018 and 2024 for Bm14 (37% to 9%) and increased for Wb123 (10% to 22%). This study identified 15 (0.5%) individuals who were seronegative to all VPDs (7 in 2018; 8 in 2019); of these, five were seronegative to all VPDs and seropositive to at least one NTD.
Conclusions/Significance
Identification of sub-populations with concurrent seronegativity to VPDs and seropositivity to NTDs underscores the potential role of multi-pathogen serosurveillance in directing public health interventions to those at greatest risk. Examination of temporal patterns offer a valuable tool for measuring intervention impacts and progress towards elimination goals.
Author Summary
Multi-pathogen serosurveillance that measures immune responses to multiple pathogens simultaneously, can enable the identification of vulnerable sub-populations with immunity gaps to vaccine preventable diseases and concurrent burden of neglected tropical disease, including those nearing elimination (lymphatic filariasis, trachoma) and eradication (yaws). In this study, we examined 2,871 samples collected from four repeated community-based surveys in Samoa in 2018, 2019, 2023 and 2024. We observed strong gains in immunity to measles following national vaccination efforts, while immunity to diphtheria declined over the same period. For yaws and trachoma, we saw very low or decreasing patterns, consistent with progress toward elimination. Patterns for lymphatic filariasis varied depending on the antibody marker used. Additionally, this study identified a small number of people with no immunity to vaccine preventable diseases and concurrent burden with at least one neglected tropical disease, underscoring the potential role of multi-pathogen serosurveillance in directing public health interventions to those at greatest risk. Examination of temporal patterns offer a valuable tool for measuring intervention impacts and progress towards elimination goals.
