The DTaP vaccine contains inactivated pieces of three bacteria: diphtheria, tetanus, and pertussis (whooping cough). Each 0.5 mL dose delivers protein fragments that train a child’s immune system to recognize these diseases, along with a small number of supporting ingredients that keep the vaccine stable and effective. None of the current DTaP formulations contain live bacteria or preservatives.
The Active Ingredients
The “active” part of any vaccine is what actually triggers an immune response. In DTaP, those are toxoids and purified bacterial proteins. A toxoid is a bacterial toxin that has been chemically deactivated so it can no longer cause harm but still looks enough like the real thing for your immune system to learn from it.
Every DTaP dose contains two toxoids: diphtheria toxoid and tetanus toxoid. These teach the body to neutralize the dangerous toxins that diphtheria and tetanus bacteria produce during infection.
The “aP” in DTaP stands for acellular pertussis, meaning the vaccine uses only selected proteins from the whooping cough bacterium rather than the whole cell. Both U.S. brands include three pertussis proteins: inactivated pertussis toxin, a protein called filamentous hemagglutinin that the bacterium uses to attach to airways, and pertactin, another surface protein. One brand (Daptacel) adds a fourth pertussis component, fimbriae types 2 and 3, which are hair-like structures on the bacterium’s surface. Together, these proteins give the immune system multiple ways to recognize a pertussis infection.
How the Two U.S. Brands Differ
Two standalone DTaP vaccines are available in the United States: Daptacel (Sanofi Pasteur) and Infanrix (GlaxoSmithKline). Both protect against the same three diseases, but their formulations aren’t identical.
Daptacel contains 15 Lf of diphtheria toxoid and 5 Lf of tetanus toxoid per dose. (Lf is a unit that measures the potency of a toxoid.) Its pertussis component includes 10 micrograms of pertussis toxin, 5 micrograms of filamentous hemagglutinin, 3 micrograms of pertactin, and 5 micrograms of fimbriae types 2 and 3.
Infanrix delivers higher amounts of the diphtheria and tetanus toxoids: 25 Lf and 10 Lf, respectively. It contains the same three core pertussis proteins but omits the fimbriae component that Daptacel includes. DTaP is also packaged inside several combination vaccines (Pediarix, Pentacel, Vaxelis, and others) that bundle it with protection against diseases like polio or hepatitis B, so your child may receive DTaP as part of a combination shot.
Aluminum Adjuvant
Both vaccines contain an aluminum salt that acts as an adjuvant, a substance that strengthens the immune response so the body builds better protection. Daptacel uses aluminum phosphate (1.5 mg per dose, providing 0.33 mg of elemental aluminum). Infanrix uses aluminum hydroxide. The aluminum content across DTaP products ranges from about 0.33 to 0.625 mg per dose.
For context, aluminum is one of the most common elements on earth and is present in breast milk, formula, and many foods. The amount in a single vaccine dose is far less than what an infant typically ingests through food and drink over the same period.
Stabilizers and Other Inactive Ingredients
Stabilizers keep the vaccine effective during storage. Daptacel uses 2-phenoxyethanol (3.3 mg per dose), a common antimicrobial also found in cosmetics and skin care products. Despite its antimicrobial properties, the FDA classifies it here as a stabilizer rather than a preservative. Infanrix uses sodium chloride, ordinary salt, as its stabilizer.
Residual Byproducts From Manufacturing
Some ingredients are used during production and then removed, leaving only trace amounts in the final product. These residuals aren’t functional ingredients; they’re leftovers from the manufacturing process.
Formaldehyde appears in both vaccines in tiny residual quantities (no more than 5 micrograms per dose in Daptacel). It is used during manufacturing to detoxify the diphtheria and tetanus toxins, converting them into harmless toxoids. The amount left over is a small fraction of what the human body naturally produces and circulates every day as part of normal metabolism.
Daptacel also contains less than 50 nanograms of residual glutaraldehyde, another chemical used in the detoxification process. Infanrix contains trace amounts of polysorbate 80, an emulsifier widely used in food and pharmaceuticals.
What DTaP Does Not Contain
Neither DTaP vaccine contains thimerosal, a mercury-based preservative that was removed from childhood vaccines in the United States in 2001. Neither contains any preservative at all. DTaP also does not contain live or whole bacteria. The “acellular” design means only purified protein fragments are used, which is why DTaP causes fewer side effects than the older whole-cell pertussis vaccines it replaced.
Some vaccines use antibiotics during manufacturing to prevent contamination, and small residual amounts can end up in the final product. Some vaccines also use fetal bovine serum as a nutrient source for growing viruses. Because DTaP is a bacterial toxoid vaccine (not a viral vaccine grown in cell cultures), its manufacturing process differs from virus-based vaccines.
Putting the Ingredient List in Perspective
A full DTaP dose is just half a milliliter of liquid, roughly one-tenth of a teaspoon. The active proteins are measured in micrograms (millionths of a gram), and the residual byproducts are measured in even smaller amounts. The aluminum adjuvant, the largest non-water ingredient, is present at a fraction of a milligram. Every ingredient serves a specific purpose: the toxoids and pertussis proteins create immunity, the aluminum adjuvant boosts that immune response, the stabilizer keeps everything intact during storage, and the trace residuals are simply what’s left after the manufacturing chemistry is done.