The only stand-alone pertussis vaccine currently available is a 2-component recombinant aP vaccine, aP5gen (Pertagen®, containing 5 μg PTgen and 5 μg FHA) that together with the Td-combined formulation tested in this trial (TdaP5gen; Boostagen®) are licensed in Thailand for immunization of adolescents and adults: both recombinant pertussis vaccines are used by pregnant women. The gene discussed is DHCR7-DT; the disease is pertussis.