The Tdap Vaccine in Pregnancy

What it contains, what the research actually says, and the questions that belong in the consent conversation

Full Drug Card → Tdap Vaccine (Maternal)

Between 27 and 36 weeks, your provider will recommend a Tdap booster — a vaccine against tetanus, diphtheria, and pertussis (whooping cough). The offer will typically sound like this: “We recommend Tdap to protect your baby from whooping cough.” What follows is what is usually not said: what the vaccine contains, what the clinical trials actually studied, what happens to your baby’s own immune response later, and what the package insert discloses that your provider likely hasn’t read aloud. You cannot consent to what you have never been told.

What is in it

Ingredients by Brand

Boostrix (GSK)

Aluminum hydroxide — 0.39 mg per dose
Formaldehyde (residual from manufacturing)
Polysorbate 80
Pertussis antigens, diphtheria toxoid, tetanus toxoid

Adacel (Sanofi Pasteur)

Aluminum phosphate — 1.5 mg per dose
Formaldehyde (residual)
Polysorbate 80
Pertussis antigens, diphtheria toxoid, tetanus toxoid

Why aluminum matters here

Aluminum adjuvant is added to vaccines to amplify the immune response — without it, the shot produces a weaker antibody response. The problem is that the route of exposure changes everything. When you swallow aluminum (from food or antacids), approximately 95% is excreted in stool before it enters your bloodstream. When aluminum is injected, approximately 95% is absorbed directly into tissue. These are not comparable exposures, and they are never compared at the point of vaccination.

Adacel contains nearly four times the aluminum of Boostrix. This distinction is almost never disclosed when the shot is offered.

What the research says

Four Things Not Disclosed at the Appointment

1 — This vaccine is not FDA-approved for use in pregnancy

Both Boostrix and Adacel are licensed for adults. Neither is FDA-approved specifically for use in pregnant women. The package inserts for both state that clinical trials did not include sufficient numbers of pregnant women to establish safety in pregnancy. The ACIP (Advisory Committee on Immunization Practices) recommends Tdap in every pregnancy based on immunogenicity modeling and observational data — not a completed randomized controlled trial in pregnant women. The distinction between “FDA-approved in pregnancy” and “recommended in pregnancy” is never explained at the point of administration.

2 — The antibodies you transfer can blunt your baby’s own vaccine response

The stated purpose of Tdap in pregnancy is to transfer your pertussis antibodies to your baby through the placenta, so your newborn has some protection before their own vaccine series begins at 2 months. A documented consequence: those same transferred antibodies can interfere with your baby’s own immune response when they receive their first DTaP shot. Healy et al. (2018, Vaccine) found that infants born to Tdap-vaccinated mothers had significantly lower pertussis antibody levels after their own vaccine series than infants born to unvaccinated mothers. The maternal antibodies are present in the infant’s bloodstream and blunt the infant’s immune response to the same antigen. This is called maternal antibody interference. It is not disclosed when the maternal Tdap is offered.

3 — Preterm birth association with co-administration

Sukumaran et al. (2018, Vaccine) found a statistically significant association between Tdap vaccination in the third trimester and preterm birth when Tdap was administered in the same visit as an inactivated influenza vaccine. The finding has not been consistently replicated in larger studies and the CDC maintains the recommendation. It has not been definitively ruled out. If your provider plans to administer both vaccines at the same appointment, this is a question worth asking.

4 — Repeated doses in multiple pregnancies have not been studied

ACIP recommends Tdap during every pregnancy — meaning a woman who has three children may receive three Tdap doses in three years. Neither Boostrix nor Adacel has completed safety trials for multiple doses across multiple pregnancies. Both package inserts specifically note that safety data for repeated administration is limited. This information is not disclosed when the shot is routinely recommended at every pregnancy visit.

Your rights

What the Compensation System Says

■Tdap is covered under the National Childhood Vaccine Injury Act (1986). Vaccine manufacturers have near-complete civil liability immunity — if you or your baby is injured, you cannot sue the manufacturer in civil court. The Vaccine Injury Compensation Program (VICP) is the exclusive legal remedy.
■Injuries that have been compensated through VICP following Tdap include: Guillain-Barré syndrome (GBS), brachial neuritis (nerve damage causing shoulder and arm weakness), SIRVA (shoulder injury from incorrect injection technique), and deaths with documented temporal relationship. Compensation has been paid to adults including pregnant women.
■The VICP filing deadline is strict: 3 years from the first symptom of injury, or 2 years from death. If you or your baby experiences a serious adverse event following vaccination, document the date and lot number immediately and file a VAERS report at vaers.hhs.gov. VICP data: hrsa.gov/vaccine-compensation/data.
■You have the right to informed refusal. No provider may administer any vaccine without your documented consent. You may decline at any point.

Before you decide

Questions to Bring to Your Provider

Which brand of Tdap are you administering — Boostrix or Adacel? Can I see the full package insert before I decide?
What is the aluminum content in this specific formulation?
I understand neither Boostrix nor Adacel is FDA-approved specifically for use in pregnancy. What is the basis for the recommendation — was this studied in randomized controlled trials in pregnant women?
I’ve read that maternal Tdap antibodies can interfere with my baby’s own pertussis vaccine response at 2 months. Is that considered in the current recommendation?
Is there a documented association between third-trimester Tdap and preterm birth when administered with the flu shot at the same visit?
I received Tdap in a prior pregnancy. What does the safety data show for a second dose? What does the package insert say about repeated administration?
If I choose to delay or decline, what monitoring is available to assess my baby’s pertussis exposure risk after birth?