The information provided below is for readers based in the United States of America. Readers outside of the United States of America should seek the information from local sources.

What is the Tetanus, Diphtheria and Pertussis (Tdap) vaccine?

Tetanus-diphtheria-pertussis (Tdap) vaccine is a shot that is given to prime the immune system to defend the individual against tetanus, diphtheria, and pertussis, all of which are diseases caused by bacteria. The Tdap vaccine consists of three components. Two of these components are the tetanus and diphtheria toxoids. A toxoid is a chemical that is similar enough to particular toxins to stimulate an immune reaction, but not similar enough to produce toxic effects. The third component of the Tdap vaccine consists of dead cells of Bordetella pertussis, the bacterial species that causes the Pertussis disease (whooping cough).

If you have received all of the recommended childhood vaccines on schedule, you will have received a childhood form of Tdap, called DTaP. It is similar to Tdap (notice that the letters are reversed), but DTaP is given only to children aged 2 months to 6 years, whereas Tdap is given to older children, teens, and adults who have not completed their DTaP immunization. Additionally, every ten years, you will have received another shot called Td, which is a booster for the tetanus and diphtheria immunizations, but not for the pertussis immunization that you had as a child. However, pregnancy is the time when you are recommended to receive Tdap (the adult form of the tetanus-diphtheria-pertussis vaccine) to serve as a booster, not only for tetanus and diphtheria, but also for pertussis, because you and your future infant are at particular risk. This vaccine is most effective if given 19-37 weeks into pregnancy.

What is the Tdap vaccine is given to prevent or treat?

Also called whooping cough (sometimes 100-day cough), pertussis is caused by a bacterial species called B. pertussis and is extremely contagious. It starts off with typical cold symptoms, such as runny nose, mild cough, and fever, but the cough worsens, lasts for weeks, and can be so powerful that it causes damage to blood vessels and lungs that can be fatal. Diphtheria is caused by Corynebacterium diphtheria and shows up as a sore throat, with a telltale thickening in the back of the throat, due to a toxin that C. diphtheria produces throughout the respiratory system. If untreated, diphtheria is deadly in up to half of all cases, because it can cause breathing difficulty, paralysis (including of breathing muscles), and heart failure.

Tetanus is caused by the bacterial species Clostridium tetani. Unlike the other two diseases, tetanus is not contagious, but as with diphtheria that effects in the body are due to a toxin produced by the bacteria. However, in contrast to C. diphtheria living inside the body and producing the toxin on site, C. tetani exists as spores (dried up cells that are in a hibernation-like state) in various substances such as soil and dust. The species also is present both as cells and spores in animal feces and saliva. In these substances, the bacteria leaves the tetanus toxin. Through a cut or puncture, a person can receive tetanus toxin, which causes painful muscle contractions throughout the body and eventually stops the breathing, resulting in death. Thus, while caused by a bacterial species, tetanus is not actually an infectious disease. Nevertheless, the vaccine to protect against tetanus works very well, not just by itself, but also in combination with vaccines to protect against diphtheria and pertussis.

Because most people in developed countries do receive their DTaP and/or Tdap and Td vaccines, these conditions are rare, but they still occur because vaccination rates are not 100 percent in all locations. In the year 2015, there were 200,000 cases of pertussis in the United States, resulting in 58,700 deaths. This is thought to represent an increase in recent years, due to a slight decrease in vaccination rates. Diphtheria used to kill many people, but now it is extremely rare; in fact zero US cases were reported in the US in 2015 (compare with 206,000 cases and 15,520 deaths in 1921), because vaccination programs have succeeded, but the organism still exists in people, because the vaccine protects against the toxin that the organisms makes without eliminating the organism. Thus, diphtheria could return as a major cause of death in the event that vaccination rates were to decline. Tetanus still kills many thousands of people each year, partly because some people are never vaccinated, and partly because immunity drops off for those who do not get their Td booster shots every ten years. 

How does Tdap vaccine work?

During the first immunization, the two toxoids in the vaccine prime the immune system against the tetanus and diphtheria toxins, while the dead B. pertussis cells prime the immune system against the B. pertussis bacterium. A second shot of the vaccine boosts the immune response, and subsequent shots remind the immune system about the toxins and B. pertussis cells, so that the ability to respond to infection or exposure to a toxin lasts for many years.

If I am taking Tdap vaccine, can it harm my baby?

No. Because Tdap is not a live vaccine, there is no concern that any components of the vaccine will replicate in your body, or in the developing baby. The potential for harm is from not receiving the vaccine or booster, because of severe consequences of neonatal forms of each of the three diseases that the vaccine is designed to prevent.

If I receive Tdap vaccine and become pregnant, what should I do?

Be happy. It is not harmful, and actually you are supposed to receive it anyway once you become pregnant. Although it is most effective for protecting the baby if given from 19-37 weeks into pregnancy, you are doing just fine if you had the shot a little early. 

If I am given Tdap vaccine, can I safely breastfeed my baby?

Yes. It is very safe. You may experience soreness in your arm, which can be uncomfortable if you are lifting and burping the infant, but there is no danger. 

If I am given Tdap vaccine, will it be more difficult to get pregnant?

The Tdap vaccine should not affect your fertility negatively.

If I am given Tdap vaccine, what should I know?

You should know that there are no live agents in the Tdap vaccine, so there is no concern about infection of the developing baby or nursing infant.

If I am taking any vaccine, what should I know?

You may find Pregistry’s expert report about vaccines during pregnancy here, reports about a variety of vaccines here, and reports about the various medications used for infections here.   Pregistry also offers blog posts about vaccines here. Additional information can also be found in the resources at the end of this report. 

Resources for Tdap vaccine in pregnancy:

For more information about Tdap vaccine during and after pregnancy, contact (800-994-9662 [TDD: 888-220-5446]) or check the following links:


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General information

It is very common for women to worry about having a miscarriage or giving birth to a child with a birth defect while they are pregnant. Many decisions that women make about their health during pregnancy are made with these concerns in mind.

For many women these concerns are very real. As many as 1 in 5 pregnancies end in a miscarriage, and 1 in 33 babies are born with a birth defect. These rates are considered the background population risk, which means they do not take into consideration anything about the health of the mom, the medications she is taking, or the family history of the mom or the baby’s dad. A number of different things can increase these risks, including taking certain medications during pregnancy.

It is known that most medications, including over-the-counter medications, taken during pregnancy do get passed on to the baby. Fortunately, most medicines are not harmful to the baby and can be safely taken during pregnancy. But there are some that are known to be harmful to a baby’s normal development and growth, especially when they are taken during certain times of the pregnancy. Because of this, it is important to talk with your doctor or midwife about any medications you are taking, ideally before you even try to get pregnant.

If a doctor other than the one caring for your pregnancy recommends that you start a new medicine while you are pregnant, it is important that you let them know you are pregnant.

If you do need to take a new medication while pregnant, it is important to discuss the possible risks the medicine may pose on your pregnancy with your doctor or midwife. They can help you understand the benefits and the risks of taking the medicine.

Ultimately, the decision to start, stop, or change medications during pregnancy is up to you to make, along with input from your doctor or midwife. If you do take medications during pregnancy, be sure to keep track of all the medications you are taking.

Read articles about TDAP