Age-related differences in antibody avidities to pertussis toxin and filamentous hemagglutinin in a healthy Japanese population

•Japanese children aged 3–6 years had low-avidity anti-PT IgG with low titers.•Vaccine-induced anti-PT IgG avidity might rapidly wane after ACVs vaccination.•Additional booster vaccination is required for children aged 3–6 years in Japan. To gain insights into the current Japanese pertussis immunization schedule, we examined the distributions of antibody titers and avidities to pertussis toxin (PT) and filamentous hemagglutinin (FHA) in 460 Japanese healthy subjects (aged 1–60 years) based on age category. Our avidity enzyme-linked immunosorbent assays revealed that young children aged 1–2 years, which corresponded to ages after receiving primary and/or booster pertussis vaccinations, had relatively high-avidity anti-PT IgG (mean avidity index [AI], 40.5%) compared with other age groups (AI, 26.5–31.9%); however, they had relatively low-avidity anti-FHA IgG (AI, 41.8%). In contrast, children aged 3–6 years had both low-avidity anti-PT IgG (AI, 26.5%) and low-avidity anti-FHA IgG (AI, 40.4%). A significant age-related difference in anti-PT IgG avidity was observed between children aged 1–2 years and 3–6 years (P