Humoral immunity 10 years after booster immunization with an adolescent and adult formulation combined tetanus, diphtheria, and 5-component acellular pertussis vaccine in the USA.

BACKGROUND: In a prospective, randomized pivotal phase III clinical trial, the immunogenicity and reactogenicity of a tetanus-diphtheria-acellular pertussis vaccine (Tdap) and a tetanus-diphtheria vaccine (Td) vaccine were studied in participants aged 11-64 years. Here we report antibody persistence through 10 years after vaccination.

METHODS: Participants who received Tdap or Td in the original phase III trial and provided pre- and post-vaccination serum samples were recruited to donate sera at 1, 3, 5 and 10 years post-vaccination. Antibody concentrations were measured using standard assay techniques.

RESULTS: Initially, 1457 Tdap and 1152 Td recipients were included; of these, 175 persons from Tdap group were available at the final study bleed point. Nearly all adolescents in both groups had diphtheria antibody levels ≥0.1 IU/mL 1 month after vaccination, which were maintained in ≥95% of vaccinees at 5 and 10 years. Among adults, ≥94% had diphtheria antibody levels ≥0.1 IU/mL 1 month after vaccination, which were maintained in ≥80% at 5 and 10 years. Nearly all participants had tetanus antibodies ≥0.1 IU/mL throughout the study. PT antibodies declined to pre-vaccination levels approximately 5 years post-vaccination; FHA, PRN and FIM antibodies waned at 5 and 10 years but remained several-fold higher than pre-vaccination levels.

CONCLUSIONS: Tdap and Td provide long-lasting protective immune responses against diphtheria and tetanus. Pertussis antibodies following Tdap generally exceeded pre-vaccination levels throughout the study, but showed substantial waning. These data may inform discussion of the need for repeat Tdap booster vaccinations among adults.

TRIAL REGISTRATION: The original phase III clinical trial, as well as the 1-, 3-, and 5-year serology follow-up studies were conducted prior to mandatory registration. The 10-year serology follow-up data collection was performed as part of a repeat Tdap administration clinical trial that was registered under clinicaltrials.gov number NCT01439165.