When two or more vaccines are administered concurrently, there is a concern on vaccine interaction, which can either enhance or suppress immune response to vaccine antigens. This study is designed to evaluate the immunogenicity and safety of tetanus-diphtheria (Td) and pneumococcal vaccines after concomitant administration in adults aged 50 years and older.

Vaccination would be the most effective strategy to prevent diverse infectious diseases. Actually, The World Health Organization (WHO) estimate that vaccination averts 2-3 million deaths per year. In adults, several vaccines are recommended based on age and medical conditions if they have not receive vaccination before, and lack evidence of past infection: influenza, measles-mumps-rubella (MMR), varicella, human papilloma virus (HPV), tetanus-diphtheria (Td), pneumococcl vaccines and etc. In particular, when the patient visits a vaccination clinic, Td and the pneumococcal vaccines are commonly administered at the same time. In this study, we aimed to evaluate the immunogenicity and safety of Td vaccine and PCV13 after concomitant administration in adults aged 50 years. This single-center, open label randomized trial was conducted (Clinical Trial Number - NCT02215863) at Korea University Guro Hospital from November 2013 to April 2016. Adults ≥50 years of age were randomized in a 1:1:1 ratio to receive Td + PCV13 (Group 1), PCV13 alone (Group 2) or Td alone (Group 3).

Inclusion Criteria:

• Adults aged ≥50 years who signed the informed consent

Exclusion Criteria:

• history of S. pneumoniae infection within the previous 5 years
• previous pneumococcal vaccination
• previous tetanus-diphtheria (Td) vaccination within the last 10 years
• known immunodeficiency or immunosuppressant use or coagulation disorders