No, Tdap is not an mRNA vaccine. It is a toxoid and protein-based vaccine, a technology that has been used in various forms for decades. The Tdap shot contains inactivated bacterial proteins that your immune system learns to recognize directly, without any genetic instructions involved. This puts it in a completely different category from the mRNA vaccines developed for COVID-19.
How Tdap Actually Works
Tdap protects against three diseases: tetanus, diphtheria, and pertussis (whooping cough). The vaccine contains two types of ingredients that train your immune system. For tetanus and diphtheria, it uses “toxoids,” which are bacterial toxins that have been chemically treated so they can no longer cause illness. Once injected, these toxoids trigger an immune response against the real toxins without making you sick.
The pertussis component works similarly but uses purified proteins taken from the pertussis bacterium. This is what “acellular” means in the vaccine’s full name: instead of using whole bacterial cells (as older pertussis vaccines did), the current version contains only two to five carefully selected proteins. Your immune system encounters these harmless proteins, builds antibodies against them, and remembers them for the future.
Two brands of Tdap are used in the United States: Boostrix, made by GlaxoSmithKline, and Adacel, made by Sanofi Pasteur. Both were first licensed in 2005. Boostrix is approved for people aged 10 and older, while Adacel is approved for ages 11 through 64. They differ slightly in their exact protein amounts but work the same way.
Why It’s Different From mRNA Vaccines
The confusion is understandable. After the COVID-19 pandemic made mRNA vaccines a household term, many people began wondering which of their other vaccines use the same technology. The answer for Tdap is none of it.
An mRNA vaccine works by delivering genetic instructions into your cells. Your cells read those instructions, build a specific protein (like the spike protein from the coronavirus), and then your immune system responds to that protein. The mRNA itself breaks down quickly and doesn’t alter your DNA, but the key point is that your own cells are doing the manufacturing.
Tdap skips that entire step. The proteins are made in a lab, purified, chemically inactivated, and placed directly into the vaccine. When you get the shot, your immune system encounters the finished proteins right away. There’s no genetic code, no cellular manufacturing, and no mRNA involved at any stage. It’s a more traditional approach: hand the immune system the thing you want it to recognize, and let it do its job.
What’s in the Shot
Each dose of Tdap contains a small, precise combination of bacterial components. Adacel, for example, includes tetanus toxoid, diphtheria toxoid, and four pertussis proteins: detoxified pertussis toxin, a protein called filamentous hemagglutinin, pertactin (an outer membrane protein), and fimbriae (hair-like structures on the bacterial surface). Boostrix contains three pertussis proteins rather than four but includes slightly higher amounts of some components.
Both vaccines also contain an aluminum-based adjuvant, which is a substance that strengthens the immune response to the proteins. Aluminum salts have been used in vaccines since the 1930s and are among the most well-studied vaccine ingredients.
Common Side Effects
Because Tdap delivers proteins directly rather than instructing cells to make them, its side effect profile reflects a straightforward immune response. The most common reactions are pain, redness, or swelling at the injection site. Some people experience a mild fever, headache, fatigue, or stomach symptoms like nausea or diarrhea. These typically resolve within a day or two.
Could an mRNA Version Exist Someday?
Researchers are exploring whether mRNA technology could eventually be used to build a next-generation version of the combined diphtheria, tetanus, and pertussis vaccine. A 2023 study published in Infection and Immunity tested a 10-antigen mRNA vaccine encoding proteins from all three diseases in rats. The mRNA version produced antibody levels comparable to the current vaccine and protected the animals against pertussis infection. It was the first preclinical study to evaluate mRNA vaccines in rats against bacterial pathogens.
That work is still in early animal testing, far from human trials or approval. The Tdap vaccine you receive today at a pharmacy or doctor’s office remains a protein-based, non-mRNA vaccine.