Prior immunological memory to pertussis toxin affects the avidity development of anti-PT IgG antibodies after acellular pertussis booster vaccination

avidity was higher in the Netherlands and United Kingdom. Despite increased anti-PT IgG concentrations in participants after vaccination, an increase in avidity was noted mainly among participants with low pre-vaccine avidity. Avidity was significantly lower in older adults in comparison to children (p<0.01) and adolescents (p=0.03) in Finnish participants one month after vaccination. Avidity after booster was influenced by the initial level of avidity, which could be linked to vaccination background, age, and prior disease exposure. The development of avidity from one month after vaccination to a year after was highly individual, with some partipants having either a decrease, an increase or a stagnant level of avidity. This emphasizes that long-term follow-up of avidity is essential. Booster vaccination seems particularly beneficial to individuals with low antibody avidity before vaccination.