Seroprevalence of antibodies against diphtheria, tetanus, and pertussis over a 12-year period in children in Kilifi, Kenya (2009-2021)
Mburu, Caroline N Ojal, John Selim, Rose Ombati, Rose Akech, Donald Karia, Boniface Tuju, James Sigilai, Antipa Smits, Gaby van Gageldonk, Peter GM
Mburu, Caroline N
Ojal, John
Selim, Rose
Ombati, Rose
Akech, Donald
Karia, Boniface
Tuju, James
Sigilai, Antipa
Smits, Gaby
van Gageldonk, Peter GM
Series / Report no.
Open Access
Type
Journal Article
Article
Article
Language
en
Date of publication
2026-01-14
Year of publication
Research Projects
Organizational Units
Journal Issue
Title
Seroprevalence of antibodies against diphtheria, tetanus, and pertussis over a 12-year period in children in Kilifi, Kenya (2009-2021)
Translated Title
Published in
Int J Infect Dis 2026:164, 108396
Abstract
OBJECTIVES: In Kilifi, pentavalent coverage remains below the 90% target, with no reported diphtheria or tetanus cases and sporadic pertussis. However, absence of disease does not guarantee immunity. To characterize age-specific gaps and waning protection not captured by routine surveillance, we conducted serial seroprevalence studies of diphtheria, pertussis, and tetanus.
METHODS: We analyzed randomly selected participants from multiple cross-sectional surveys within the Kilifi Health and Demographic Surveillance System. Immunoglobulin G antibodies were measured using a fluorescent bead-based multiplex immunoassay applying protective thresholds ≥0.011 IU/ml for diphtheria and tetanus. Pertussis antibodies were grouped by time since infection. Bayesian multilevel regression with post-stratification adjusted estimates for population structure and assay performance; associations with age and year were assessed using logistic regression.
RESULTS: Diphtheria seroprotection was low; only 5% of children had long-term seroprotection, with full protection ranging from 11% to 34% and minimal seroprotection from 40% to 52%. Minimal seroprotection increased over time (τ = 0.68, P = 0.04). Tetanus protection was higher, with long-term seroprotection ranging from 10% to 39% and susceptibility <1%; trends were not significant. Older age was associated with lower seroprevalence. Among adults, <1% had long-term diphtheria seroprotection vs 36% for tetanus. Pertussis circulation was minimal, with 5% of children and <1% of adults, with antibody concentrations consistent with recent infection.
CONCLUSIONS: Although conventional serological thresholds suggest immunity gaps, particularly, for diphtheria, no diphtheria or tetanus outbreaks have occurred in Kilifi over the past decade. This indicates that antibody concentrations below standard thresholds may not equate to immediate susceptibility, but they do reflect a narrower margin of population immunity. Although this has not yet translated into disease, it could become relevant if transmission conditions change, underscoring the need to sustain high vaccination coverage and sensitive surveillance. Serology should, therefore, be viewed as a complementary tool, useful for tracking emerging vulnerability and informing future booster decisions if susceptibility increases.