Cohort description.

1 aP and wP; acellular or whole cell pertussis vaccine; 2 ‘time since exposure’ is either time between blood sampling and episode of symptomatic pertussis infection or time between blood sampling and last (aP or wP) vaccination, following an earlier episode of symptomatic pertussis; 3 all had wP(1–4) as primary series except two participants who had aP(1–4) and 1 participant who had wP(1–3), aP(4); 4 all had wP (1–4) as primary series except three participants who had aP(1–4) and 1 participant who had wP(1–3), aP(4); 5 all had wP (1–4) as primary series except two participants who had aP(1–4) and 1 participant who had wP(1–3), aP(4).