In pregnant women who are not fully immunized, should tetanus‑diphtheria (Td) vaccine or tetanus toxoid (TT) be administered?

Tdap Should Be Given During Pregnancy, Not TT Alone

In pregnant women who are not fully immunized, Tdap (tetanus-diphtheria-acellular pertussis) vaccine should be administered during each pregnancy, preferably between 27-36 weeks gestation, rather than TT (tetanus toxoid) alone. 1, 2

Current Guideline Recommendations

The CDC and ACIP clearly recommend one dose of Tdap between 27-36 weeks of gestation during each pregnancy, regardless of prior tetanus immunization status 1, 2. This represents a shift from older practices that used standalone tetanus toxoid (TT).

Key Rationale for Tdap Over TT:

• Dual protection: Tdap protects both mother and infant against tetanus, diphtheria, AND pertussis—the latter being critical as pertussis causes severe morbidity and mortality in young infants 1
• Maternal antibody transfer: Vaccination during the third trimester optimizes transplacental antibody transfer to the newborn, providing passive immunity during the vulnerable first months of life before the infant's own vaccination series begins 1, 3
• Pertussis resurgence: Cases rose from 7,857 in 2000 to over 48,000 in 2012 in the US, with highest rates in infants too young for vaccination 1

Practical Implementation Algorithm

For pregnant women with unknown or incomplete tetanus immunization:

1. Primary series needed (fewer than 3 prior doses):

   • Give Tdap as the first dose, preferably at 27-36 weeks
   • Complete the 3-dose series with Td for remaining doses (if time permits during pregnancy) 4, 5
   • If only one dose can be given during pregnancy, make it Tdap in the third trimester

2. Previously immunized (completed primary series):

   • Give Tdap at 27-36 weeks regardless of interval since last tetanus-containing vaccine 2, 3
   • The 2010 ACIP guidance eliminated the need to delay Tdap based on interval from prior Td 2

3. Each subsequent pregnancy:

   • Repeat Tdap during each pregnancy, even if received in a prior pregnancy 1, 2, 3

Important Caveats

• Timing flexibility: While 27-36 weeks is optimal, Tdap can be given at any point in pregnancy if the woman presents late for care 1
• Safety profile: Tdap is an inactivated vaccine with no evidence of adverse fetal effects 3, 6. A large study examining specific birth defects found no increased risk (aOR 1.0,95% CI 0.7-1.5 for first trimester exposure) 6
• WHO context: In resource-limited settings where neonatal tetanus remains endemic, WHO still recommends TT/Td if Tdap is unavailable, with at least one dose given ≥2 weeks before delivery 1. However, in high-income countries where Tdap is available, it is the clear preference

Why Not TT Alone?

The "cocooning" strategy (vaccinating contacts of infants) proved poorly effective 1. Maternal vaccination during pregnancy is far more cost-effective and provides direct passive immunity to the newborn when they are most vulnerable. Using TT alone misses the critical opportunity to protect against pertussis, which causes the highest morbidity and mortality in infants under 6 months.

Bottom line: Tdap during every pregnancy (27-36 weeks) is the standard of care in settings where it is available. 1, 2, 3