How many doses of Tdap (Tetanus, diphtheria, and pertussis) vaccine are typically administered?

Tdap Vaccination: Number of Doses Required

Tdap (Tetanus, diphtheria, and pertussis) vaccine is typically administered as a single dose for adolescents and adults, while children under 7 years receive a series of 5 DTaP doses. 1

Age-Specific Tdap Dosing Recommendations

Children Under 7 Years

• Children receive DTaP (not Tdap) as a 5-dose series:
  • Primary series: 3 doses at 2,4, and 6 months
  • First booster: 15-18 months
  • Second booster: 4-6 years
• Maximum of 6 doses of diphtheria and tetanus toxoid-containing vaccines should not be exceeded before age 7 1

Adolescents (Ages 7-18 Years)

• One dose of Tdap as part of the catch-up series if not fully immunized with DTaP
• If additional doses needed, Td (tetanus-diphtheria) vaccine should be used 1
• For those who received Tdap as part of catch-up at ages 7-10 years, another adolescent Tdap dose should be administered at age 11-12 years 1

Adults (Ages 18+ Years)

• One dose of Tdap for those who have never received it
• For adults never vaccinated against tetanus, diphtheria, or pertussis: 3-dose series with only one containing pertussis (Tdap)
  • Preferred schedule: Tdap first, followed by Td ≥4 weeks later, then another Td 6-12 months later 1
  • Tdap can substitute for any one of the Td doses in the 3-dose primary series 1

Special Situations

Pregnancy

• One dose of Tdap during each pregnancy, preferably between 27-36 weeks gestation 1
• For unvaccinated pregnant women: at least 2 properly spaced doses of tetanus toxoid-containing vaccine during pregnancy (one should be Tdap) 1

Healthcare Personnel

• Single dose of Tdap for all healthcare personnel who have not previously received it 1
• After Tdap, routine Td boosters according to recommended schedule 1

Wound Management

• If more than 5 years since last tetanus toxoid-containing vaccine, Tdap is indicated for persons ≥11 years who have not previously received Tdap 1

Revaccination with Tdap

While Tdap was originally licensed for single-dose administration, more recent evidence supports the safety and immunogenicity of repeat Tdap vaccination:

• A 2019 randomized controlled trial demonstrated that a second dose of Tdap in adults approximately 10 years after the first dose was well tolerated and immunogenic 2
• Antibody levels to pertussis antigens begin to decline by 5 years after Tdap vaccination 3

Common Pitfalls and Caveats

1. Confusing DTaP and Tdap: DTaP is for children under 7 years; Tdap is for individuals 7 years and older. The lowercase letters indicate reduced antigen content appropriate for older individuals.

2. Administering multiple Tdap doses unnecessarily: Generally, only one dose of Tdap is recommended for adolescents and adults, with Td used for subsequent boosters, except during pregnancy.

3. Missing documentation: For adults with unknown vaccination history but likely previous vaccination, serologic testing can be considered. If tetanus and diphtheria antitoxin levels are >0.1 IU/mL, previous vaccination is presumed, and only a single dose of Tdap is indicated 1.

4. Exceeding maximum doses in children: No more than 6 doses of diphtheria and tetanus toxoid-containing vaccines should be administered before age 7 due to increased risk of adverse reactions 1.

5. Inadvertent administration: If Tdap is inadvertently administered instead of DTaP for one of the first 3 doses in young children, it should not be counted as valid, and a replacement dose of DTaP should be given 1.

Tdap provides critical protection against pertussis in addition to tetanus and diphtheria, making it an important component of the immunization schedule for all age groups.