Seroprevalence of antibodies against diphtheria, tetanus, and pertussis over a 12-year period in children in Kilifi, Kenya (2009-2021)

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.