Immunogenicity and Safety of GlaxoSmithKline (GSK) Biologicals' Boostrix™ Vaccine in Previously Boosted Young Adults

Subjects were previously vaccinated with either Boostrix or a control Td vaccine in study NCT00109330. Only subjects who were part of the primary study will be invited to participate in this study. All subjects will receive a single dose of Boostrix at Visit 1 (Day 0) and subjects will be observed till Visit 2 (Day 30) for safety in terms of solicited adverse events (during 4 days post vaccination), unsolicited adverse events (during 31 days post vaccination) and serious adverse event (during the trial period). A blood sample will be collected from all subjects before vaccination (Visit 1) and one month after vaccination (Visit 2) for antibodies estimation. This summary has been updated following Protocol amendment 2 dated 03 October 2013. The protocol is being amended to facilitate enrolment by: * \- Extending the window period for re-vaccination from ± 6 months to ± 300 days from the Year 10 time point. * \- Extending the recruitment period from 6 months to 14 months. The format of non-inferiority criterion of the first co-primary objective has been updated to keep it aligned with the format of non-inferiority criterion of the second co-primary objective.