The TDAP vaccine does not cause autism or make it more likely that a child will develop autism.

What Is the TDAP Vaccine?

The TDAP vaccine is a combination booster shot. It is administered to children and adults, to protect them from three diseases: pertussis, tetanus, and diphtheria. The name of the vaccine derives from the conditions it provides immunization from: T for tetanus, D for diphtheria, and P for pertussis. 

Tetanus is a bacterial infection that enters the body through a cut or wound. It targets the brain and central nervous system, causing muscle spasms so severe it can make it impossible for patients to open their mouths. For this reason, tetanus is also referred to as “lockjaw.” Around 20% of patients infected with tetanus will die. 

Diphtheria is another bacterial infection that enlarges the lymph nodes. It results in extreme swelling around the neck that makes it difficult to breathe. In extreme cases, patients can experience damage to their nerves and heart, as well as kidney problems and paralysis. 

Pertussis is also known as whooping cough because of the severity of the coughing fits it induces, so much so that patients could pass out and break their ribs. People with pertussis have to take drastically deep breaths to regain oxygen they lose from a coughing fit, which sounds like a “whoop,” hence the name. 

The Centers for Disease Control and Prevention writes that there are two TDAP vaccines authorized for use in the United States, known by the brand names Adacel (produced by Sanofi Pasteur) and Boostrix (GlaxoSmithKline). Both brands contain trace and deactivated elements of the bacteria that cause the TDAP diseases. This is enough to train the immune system to produce the proteins (the antibodies) to fight the diseases upon exposure.

TDAP & Autism: Is There a Connection?

There is no connection between the TDAP vaccine and the development of autism spectrum disorder (ASD).

A 2018 study in the journal Pediatrics examined the vaccine because doctors had recommended it be given to pregnant women to protect their children against tetanus, diphtheria, and pertussis. Researchers found no connection of increased risk between the prenatal vaccination and the development of autism in their offspring. 

Additionally, the researchers went on to support the administration of the TDAP vaccine in pregnant mothers, noting that it offered protection from infections that could lead to neurodevelopmental disorders later in the child’s life. 

Misconceptions & Actual Risks

One of the challenges the researchers noted is the degree of misconceptions surrounding the use of vaccines, which has led many women to avoid getting necessary vaccines while they are pregnant and declining to vaccinate their children. This poses a much greater risk than any fear of the development of autism disorders because children who are not vaccinated are vulnerable to preventable diseases.

Researchers say that the risk of an infant getting pertussis and having adverse events (which could culminate in death) is a significant concern. Maternal infections can create an immune response that disrupts brain development of the fetus, which can increase the risk level for autism. 

Largely due to misunderstandings and misinformation, this has also led parents and activists to question whether vaccinations (like the TDAP vaccine) against those maternal infections can influence their offspring being born with ASD. 

The Pediatrics study is one of many studies to repeatedly find vaccines do not pose any risk of autism. Researchers hope the overwhelming weight of evidence might convince some mothers and families to trust the science behind vaccinations. If they do, they can easily protect their unborn children from these diseases.

The director of the Vaccine Education Center at Philadelphia’s Children’s Hospital explained that the risk isn’t about autism, but that “the child won’t be protected against pertussis.”

The History of Vaccine Skepticism & Autism

Notwithstanding the consensus that the TDAP vaccine has no connection to autism, researchers know they still face an uphill public health battle.

In spite of the ongoing COVID-19 pandemic — and, in some cases, because of it — there is widespread resistance to vaccination, ranging from skepticism to outright hostility. Doctors and researchers fear the hesitance to vaccinate children could lead to certain diseases being reintroduced into the general population, like the 2014–2015 measles outbreak in California

What muddies the waters is that much about autism remains unknown, including what causes it. These gray areas are often the source of misinformation that spreads on social media, erroneously and misleadingly connecting anecdotes, outlier cases of negative response, and sensationalized misunderstandings of the chemical compositions of vaccinations with neurodevelopmental challenges in some children. 

Ultimately, however, no scientific research in the modern era has produced any evidence that there is a connection between vaccinations, like the TDAP vaccine, and the development of autism.

The original study that linked autism to vaccines has been withdrawn and debunked. The scientist who made the connection did so in bad faith, and he was stripped of his medical license. He is no longer allowed to practice medicine in his home country of the United Kingdom. 

The unanimous findings among researchers is that children will be worse off if their mothers decline the vaccine. While there is no risk the children will develop autism if they receive the shot, there is every risk that the children might develop tetanus, diphtheria, or pertussis if they don’t.