In July 2015-November 2016, a phase II/III randomized, observer-blind,controlled study of two acellular Pertussis vaccines (aP standalone and TdaP combined vaccined) manufactured by BioNet-Asia Co., Ltd. (Bionet) and chemically-detoxified Adacel Tdap vaccine was conducted in Bangkok, Thailand in healthy subjects aged 12-17 years (Protocol No. TDA202; http://clinicaltrials.in.th; Study ID:TCTR20150703002). A total of 450 subjects were enrolled into the study at 2 study sites (Site No.1:Faculty of Medicine Siriraj Hospital; Site No.2:Vaccine Trial Centre (VTC), Faculty of Tropical Medicine, Mahidol University) with equal number of 225 subjects enrolled at each study site. During the study, the subjects had been randomized in a 1:1:1 ratio to received intramuscularly a booster dose (0.5 mL) of the study vaccines.

In this current study, persistence of pertussis antibodies induced by a booster dose of recombinant acellular Pertussis based vaccines (Pertagen and Boostagen) manufactured by Bionet will be evaluated and compared to the conventional chemically-detoxified Tdap vaccine (Adacel) at 2 years after previously immunized in the TDA202 study.

The study population will included all subjects who participated in the TDA202 study at the Vaccine Trial Centre (VTC), Faculty of Tropical Medicine, Mahidol University, Bangkok.

This is further follow-up from TDA202 clinical trial, which was completed on 29 November 2016. Target population for this study is the group of subjects who had received one dose of one of the three study vaccines in the TDA202 trial at site VTC and who had completed the study follow-up at 1-year after vaccination (223 subjects).

The subjects who had received a single dose of one of the 3 study vaccines and completed 1-year follow-up visit at Day 336±28 during the TDA202 study will be called for consent process at 2 years after vaccination based on Vaccination Date in TDA202 study within ±1 month window period. Subjects aged ≥ 18 years who have signed the written informed consent form or subjects aged < 18 years who have signed the assent form with their parent/legal guardian's given written informed consent will be screened for general health status and those who fulfill all inclusion and exclusion criteria will be enrolled into the study.

Once enrolled, blood sample (approximately 5 mL) will be taken from all subjects. After blood collection, vaccination with a licensed influenza vaccine will be offered to all subjects.Blood samples will be processed for serum separation and shipped to Bionet Human Serology Laboratory where immunogenicity testing (ELISA antibodies against tetanus, diphtheria, Pertussis Toxin (PT) and Filamentous hemagglutinin (FHA) and PT neutralizing antibody by Chinese Hamster Ovary (CHO cell assay) will be performed . ELISA testing to detect antibodies against tetanus, diphtheria, and pertussis antigens (PT and FHA) will be performed for all enrolled subjects while CHO cell assay to detect PT neutralizing antibody will be performed only in the same subset of 75 subjects (25 subjects in each vaccine group) who had been selected for PT neutralizing antIbody assessment in the previous TDA202 study.

Statistical analysis will be performed to evaluate antibody persistence at 2 years after one dose of each study vaccine given to subjects during the previous TDA202 study.

Data management and statistical analysis will be performed by Center of Excellence for Biomedical and Public Health Informatics (BIOPHICS), Bangkok, Thailand.

Inclusion Criteria:

1. Having participated in TDA202 study, received a single dose of one of the 3 study vaccines, and completed 1 year follow-up visit.
2. Written informed consent is obtained for subjects aged ≥18 years, or written assent and written informed consent are obtained from subjects aged <18 years and from their parent/legal guardian, respectively, prior to study entry.
3. Capable to comply with study procedures and willing to provide with a blood sample.

Exclusion Criteria:

1. Received lived attenuated vaccine within 3 months prior to participating in this study.
2. Received vaccines other than lived attenuated vaccine within 28 days prior to participating in this study.
3. History of receiving blood or blood component or immunoglobulin within 3 months prior recruitment
4. History of receiving immunosuppressive drugs or systemic corticosteroid (>0.5 mg/kg of prednisolone or equivalent for more than 14 days) within 3 months prior to recruitment.
5. Received diphtheria or tetanus or pertussis vaccine within 1 year prior to inclusion in the present study.

The target population for this study is the group of subjects who had received one dose of acellular pertussis based vaccine in TDA202 trial at Vaccine Trial Centre (VTC), Faculty of Tropical Medicine, Mahidol University and who had completed the study follow-up at 1 year after vaccination.