F2 and pertussis: In those adolescents, the implication based on current understanding is that low levels of IgG-anti-PT correlate with disease susceptibility, seropositivity to IgG-anti-PT indicates preceding natural infection, and the detection of high IgG-anti-PT concentration indicates recent or active infection due to the well-established waning of pertussis vaccine-induced immunity [4,5,6,7,8,9,14,15].