Overview

Tdap is an inactivated vaccine that protects you against three different illnesses: tetanus, diphtheria, and pertussis. Pertussis is commonly known as whooping cough. The Tdap vaccine is recommended between 27 and 36 weeks of pregnancy. The main reason any vaccine is recommended during pregnancy is for the passive immunity your baby receives. Vaccines are a complex and often controversial topic. This episode follows a systematic approach that includes thorough research to evaluate the safety and efficacy of the Tdap vaccine.

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What is a Vaccine?

To better understand how vaccines work and the risks and benefits associated with them, let’s first cover some basics. Traditionally, vaccines are made using a weakened or killed version of a disease-causing microorganism or parts of it, like its toxins or surface proteins. When given, typically through an injection, vaccines trigger your immune system to produce antibodies against the disease without causing illness. Essentially, the vaccine teaches your body to recognize and fight the disease if you encounter it in the future. In some cases, immunity lasts a lifetime; in others, booster shots may be necessary to maintain protection.

Types of Vaccines

Different types of vaccines use different methods to stimulate immunity. Inactivated vaccines use micro-organisms that have been killed, often through heat, radiation, or chemicals. The flu vaccine and pertussis (whooping cough) vaccine are examples. Attenuated vaccines contain live but weakened micro-organisms. These are strong enough to trigger an immune response but not enough to cause illness. Toxoid vaccines use inactivated toxins from bacteria, such as those in the Tdap vaccine, which protects against tetanus and diphtheria. Subunit vaccines use specific proteins or pieces of the pathogen to trigger an immune response. This method is used for certain vaccines like the HPV vaccine. mRNA vaccines, a newer technology used for COVID-19 vaccines, work differently. Instead of using part of the virus or bacteria, these vaccines instruct your cells to make a protein that triggers an immune response. This teaches your immune system to recognize and fight the virus if you are exposed to it in the future.

Vaccine Ingredients

Vaccines often contain additional ingredients to ensure safety and effectiveness. Adjuvants like aluminum salts help boost the immune response to the vaccine. Stabilizers are used to maintain the vaccine’s potency during storage and transport. Preservatives are used in multidose vials to prevent contamination. Thimerosal, a mercury-containing preservative, has been used in some multidose flu vaccines. Lipid nanoparticles (tiny fat particles) are included in mRNA vaccines to protect the fragile mRNA and help it enter your cells. Other vaccines may contain trace amounts of antibiotics to prevent bacterial growth, formaldehyde (used to inactivate toxins or kill viruses and bacteria during the production process), and in some cases, egg proteins, if the virus is grown in eggs, as is the case for certain flu vaccines. Vaccines can have a lot of ingredients. This article will dive deep into the safety of the Tdap vaccine and talk about the specific components included in your options for that vaccine.

Immunity

Different forms of immunity can result from vaccination. Individual immunity occurs when a single person develops immunity after receiving a vaccine. Passive immunity happens when a pregnant mother passes antibodies to her baby through the placenta or later through breast milk, providing the baby with temporary protection. This is a big driver for vaccines recommended during pregnancy. Herd immunity occurs when a large portion of the population is vaccinated, reducing the spread of disease. Herd immunity is crucial for protecting individuals who cannot get vaccinated, such as those with compromised immune systems, allergies to vaccine ingredients, or babies too young to be vaccinated. Herd immunity only applies to contagious diseases and plays a significant role in preventing outbreaks and eradicating illnesses.

Evaluating Vaccines

I follow a systematic approach and conduct thorough research when evaluating any vaccine or medical intervention. I ask several key questions:

• What are the risks of the illness the vaccine is targeting?
• What is the history of the vaccine?
• What ingredients are in the vaccine?
• How effective is it?
• What are the risks and benefits?

In addition to these general questions, I consider personal factors like my current health status, the likelihood of exposure, where I live, places I may travel to, and the time of year. Answering these questions requires a significant amount of research and critical thinking.

The Controversy Surrounding Vaccines

Vaccines are a complex and often controversial topic. Some professionals dedicate their careers to researching and studying vaccine safety and efficacy. This makes researching vaccines challenging, as it’s easy to come across information that appears unbiased but may ultimately push a pro- or anti-vaccine agenda. This episode aims to provide an objective overview of the data so you can make an informed decision that’s right for you. If you have additional questions or concerns, discussing them with your doctor or midwife is always best.

The Role of the Centers for Disease Control and the World Health Organization 

In recent years, there have been growing questions about the reliability of information from organizations like the CDC and WHO and the potential influence of pharmaceutical companies on these organizations. However, it’s important to note that the CDC and WHO maintain some of the most extensive centralized databases for disease statistics. While these organizations focus on protecting public health on a national and global scale, their guidelines often inform recommendations by bodies like the American College of Obstetricians and Gynecologists (ACOG), which, in turn, influence your healthcare provider’s advice. Ultimately, your primary concern is the safety and efficacy of a vaccine for you and your baby. Understanding the information that informs your doctor’s or midwife’s recommendations will equip you to have an educated conversation with them and help you make the best decision for your pregnancy.

Tdap Vaccine

Tdap is an inactivated vaccine that protects you against three different illnesses: tetanus, diphtheria, and pertussis. Pertussis is commonly known as whooping cough. The Tdap vaccine is recommended between 27 and 36 weeks of pregnancy.

Tetanus

Tetanus comes from the clostridium bacteria, which lives in soil contaminated with manure from animals or humans. This bacteria is dormant in the soil, and it can enter your body through a cut on your skin. It germinates or becomes active in an anaerobic environment, which means there is no oxygen. We often think of tetanus coming from stepping on a rusty nail. In this case, the sharp nail creates a deep puncture wound and a great anaerobic environment. The rusty nail is dirty and theoretically contaminated with this bacteria. Tetanus causes painful muscle tightening and stiffness, usually all over the body. It can lead to tightening muscles in the head and neck, so you can’t open your mouth, swallow, or even breathe. Tetanus is sometimes known as lockjaw.

The good news is that tetanus is rare in the United States today. The bad news is that it can be lethal. Since 2000, there have been less than 50 reported cases each year in the United States. In other parts of the world, tetanus is more common, and the World Health Organization estimated that in 2018 25,000 newborns died from neonatal tetanus. The vast majority of these cases are in areas where access to resources is limited and tetanus rates are much higher than in the U.S.

Diptheria

Diphtheria is extremely rare in the United States today. From 1996-2018 there were only 14 reported cases in the U.S. This was a much bigger issue before the introduction of vaccines. It is more common in other parts of the world, and nearly 25,000 cases were reported in 2023 to the WHO. Diphtheria can cause a thick coating to form in the back of the throat, leading to breathing problems, heart failure, paralysis, and death. 

Pertussis

The main aim of the Tdap vaccine in the United States is pertussis, also known as whooping cough, and is a highly contagious respiratory tract infection. Airborne bacteria cause this infection when an infected person coughs or sneezes. Within ten days of becoming infected, the first signs are a runny nose, nasal congestion, red, watery eyes, fever, and cough. After a week or two, signs and symptoms worsen. Thick mucus accumulates inside your airways, causing uncontrollable coughing. When an infant has pertussis, they may not cough at all, and they may just struggle to breathe or temporarily stop breathing. Infants are at the most significant risk of complications from pertussis.

We know that pertussis can be dangerous for young babies. Let’s examine the prevalence of this illness. The last time we had a major outbreak of pertussis was in 2012, with 48,277 reported cases. From 2013 through 2019 there was an average of about 22,000 cases per year. The prevalence of pertussis dropped dramatically during the COVID-19 pandemic, in 2022 there were only about 3,000 reported cases. According to the CDC, whopping cough cases are on the rise in 2024, and the United States is beginning to return to pre-pandemic patterns where more than 10,000 cases are typically reported each year. While 10,000 cases is a lot, this is far less common than other illnesses, like the flu which has tens of millions of cases each year.

Why is the Tdap Vaccine Recommended During Pregnancy? 

It may seem strange that the Tdap vaccine is recommended during pregnancy because two of the three illnesses it protects against are nearly non-existent. The main reason Tdap is recommended is for pertussis (whooping cough) and for the passive immunity your baby receives. Pertussis can be a severe health concern for babies. The younger a baby gets pertussis, the more likely it will need to be treated in the hospital. In 2023, of the 376 children under six months diagnosed with pertussis in the U.S., 21.2% were hospitalized. There were a total of three deaths, and two of those were children under the age of one.

For children, the vaccine that targets pertussis is the DTaP vaccine, which also includes diphtheria and tetanus. The first dose is not recommended until two months of age. If you receive the Tdap vaccine, you can give your baby passive immunity for the first two months. There is no vaccine that only targets pertussis; the only vaccines available combine pertussis with tetanus and diphtheria.

Official Recommendations

The American College of Obstetricians and Gynecologists recommends that all pregnant women receive the Tdap vaccine between 27 and 36 weeks of pregnancy, as early in that window as possible. ACOG states that the Tdap shot is a safe and effective way to protect you and your baby from serious illness and complications of pertussis. The American College of Nurse-Midwives also recommends the Tdap vaccine during pregnancy. The American Academy of Pediatrics also supports the Tdap vaccine during pregnancy. They cite a study that found the maternal Tdap vaccine was 91.4% effective during the infant’s first two months of life and 69% effective during the child’s entire first year. 

Protecting Your Baby 

Your baby is born without much of an immune system. When you get the Tdap vaccine, the passive immunity your baby receives should protect it until it is old enough to receive the vaccine, around two months. The antibodies your body creates are highest two weeks after you receive the vaccine. The goal of having the vaccine by week 36 is so you can pass antibodies to your baby before they are born.

The American College of Obstetricians and Gynecologists goes even further to recommend adolescent family members or caregivers should get the Tdap vaccine at age 11 to 12. If adult family members or caregivers have never had the Tdap vaccine, they should get it at least two weeks before having contact with your baby. This makes a safety “cocoon” of vaccinated caregivers around your baby. The American College of Nurse-Midwives also advises that adults who will be around newborns be vaccinated against pertussis.

The latter part of this recommendation may pose some additional challenges. It is one thing to decide if you want a vaccine and another to recommend your family or anyone spending time around your new baby get the vaccine.

Evidence on the Safety of the Tdap Vaccine During Pregnancy 

In recent years, several studies have looked at the safety of the Tdap vaccine during pregnancy. An observational study in California included over 123,000 expecting mothers, of which 21% received the Tdap vaccine. The researchers found that vaccination was not associated with increased risks of adverse birth outcomes. They specifically looked at small for gestational age births, chorioamnionitis, preterm birth, and hypertensive disorders of pregnancy. The researchers detected an increased risk of being diagnosed with chorioamnionitis following vaccination. It was 6.1% in the group that received the Tdap shot and 5.5% in the group that did not. Chorioamnionitis is a bacterial infection that occurs in the membranes of the amniotic sac or the amniotic fluid.

A systematic review looked at the safety of this vaccine, and I was on the fence about including the abstract here. It is frustrating when research is behind paywalls because it can be expensive to access these studies, and I cannot share them publicly to give you full access after I have purchased them. I am careful to read complete studies and not go off of abstracts or summaries, which is no exception. Plus, this study was in part funded by the two manufacturers who produce this vaccine. I always look for biases or conflicts of interest when evaluating research, and it is worth noting who supported this review. The conclusion of this study states that evidence suggests that Tdap administered during the second or third trimester of pregnancy is not associated with clinically significant harms for the fetus or neonate. Medically attended events in pregnant women are similar between vaccinated and unvaccinated groups. These results come as no surprise. It is rare that research funded by a pharmaceutical company is published if it finds evidence that could damage the companies that funded grants to support the research. Perhaps I am a bit skeptical here, and I like to look at any study with a critical eye. Overall, the results of this review are good news. 

There were some additional takeaways from this study that are worth mentioning. Rates of fever following the vaccine ranged between 1% and 3%. Headache ranged from 2.8–33%, malaise (feeling under the weather or tired) 0.4–33%, myalgia, muscle aches, and pains 0.8–24%. In this review, they note that the wide range between rates identified in the studies is likely to result from the different methods used to identify adverse events, definitions, and variability expected from small sample sizes. The reporting of these side effects in the clinical trials for Adacel and Boostrix tended to be at the upper end or over the rates found in these studies.

This review also addresses a great point that we should consider when looking at studies during pregnancy. They note that observational research has been the mainstay of evidence available for women vaccinated during pregnancy. They say that although observational evidence is integral when assessing harms, the lack of placebo-controlled randomized controlled trials means it is critical to understand the limitations of the evidence presented in the findings of this review. This results from the comparative cost, ethical considerations, and underrepresentation of pregnant women in clinical trials. 

Observational studies are always ongoing. Both manufacturers maintain a pregnancy exposure registry that monitors pregnancy outcomes in women exposed to these vaccines during pregnancy.

Comparing Your Vaccine Options

Two manufacturers make the Tdap vaccine. Both were approved and have been in use since 2005.

Adacel made by Sanofi Pasteur

The ingredients per 0.5 mL dose include 1.5 mg aluminum phosphate (0.33 mg aluminum) as the adjuvant, ≤5 mcg residual formaldehyde, <50 ng residual glutaraldehyde and 3.3 mg (0.6% v/v) 2-phenoxyethanol (not as a preservative).

A retrospective passive surveillance study suggests the rates of major birth defects and miscarriage in women who receive Adacel within 30 days prior to pregnancy or during pregnancy are consistent with estimated background rates. Two developmental toxicity studies were performed in female rabbits given 0.5 mL (a single human dose) of Adacel twice prior and during gestation. The studies revealed no evidence of harm to the fetus due to Adacel.

Boostrix GlaxoSmithKline

Each 0.5-mL dose contains aluminum hydroxide as adjuvant (formulated to contain 0.3 mg aluminum) and 4.4 mg of sodium chloride. The aluminum content is measured by assay. Each dose also contains ≤100 mcg of residual formaldehyde and ≤100 mcg of polysorbate 80 (Tween 80).

A randomized, controlled study of 687 pregnant individuals was done on the non-U.S. formulation of BOOSTRIX. The only difference between the non-US formulation and the formulation in the United States is the non-US formulation contains more aluminum. So the safety data should be relevant. There were no identified vaccine-related adverse effects on pregnancy or on the fetus/newborn child. There were also three separate animal studies that revealed no evidence of harm to the fetus due to BOOSTRIX.

Vaccine Ingredients

Both of these vaccine formulations are very similar, and one is not recommended over another. Both contain ingredients in addition to the antigens for tetanus, diphtheria, and pertussis. Aluminum is included in both formulations to boost your immune response to the vaccine, and the amounts are very similar; Boostrix has 0.03mg less aluminum. Both have residual formaldehyde, which is used as part of the manufacturing process to inactivate the toxins produced by the bacteria that cause these diseases. While formaldehyde sounds like a scary ingredient, the amount of formaldehyde in vaccines is much lower than that naturally produced in the human body during normal metabolic processes. Boostrix has ≤100 mcg of residual formaldehyde, while Adacel has ≤5 mcg.

Adacel includes glutaraldehyde to inactivate bacterial toxins and kill bacteria during the manufacturing process. It also contains 2-phenoxyethanol as a stabilizing agent. While 2-phenoxyethanol can sometimes be used as a preservative, Adacel states explicitly that this ingredient is not included as a preservative. In this case, it is included to contribute to the overall stability of the vaccine.

Boostrix includes sodium chloride (common table salt) to help maintain the proper osmotic balance and stability of the vaccine solution to ensure that the vaccine is isotonic. By keeping the vaccine isotonic, sodium chloride helps prevent irritation at the injection site without causing adverse reactions due to differences in fluid balance between the vaccine and the body. This formulation also includes polysorbate 80 as an emulsifier and stabilizer. Its primary role is to help mix the ingredients in the vaccine evenly and maintain the stability of the vaccine components.

Some of these ingredients may sound dangerous and intimidating, but all have undergone rigorous safety testing and are necessary for the vaccine’s safety, stability, and effectiveness. Both the Boostrix and Adacel are similar and both are approved for use during pregnancy. If you prefer a specific brand of vaccine, please talk with your doctor or midwife. 

Combining Tdap and Other Vaccines 

If you opt to get the Tdap vaccine, another consideration is whether to get it simultaneously with other vaccines. There are four vaccines recommended during pregnancy:

1. COVID-19 as soon as possible in any trimester
2. Flu in any trimester as early as possible during flu season (October-May)
3. RSV if you are between 32 and 36 weeks of pregnancy from September through January
4. Tdap in the third trimester

According to the American College of Obstetricians and Gynecologists, you can get Tdap, flu, RSV, and COVID-19 shots in the same visit and getting these vaccines at the same time is safe.

In one of the clinical trials disclosed in the Adacel Tdap vaccine package insert, they found that when the Adacel vaccine was administered simultaneously as a trivalent inactivated influenza vaccine, a lower antibody response was observed for pertactin antigen compared to when the Adacel vaccine was administered alone. The pertactin antigen is one of the things that help you develop immunity for pertussis. Despite these findings, the Tdap and flu vaccines are often combined.

Every vaccine has possible side effects like pain and swelling at the injection site. It would seem logical that these side effects could be more substantial if you get multiple vaccinations in one visit. I was unable to locate research on combining multiple vaccines in pregnancy. You can always choose to space them out. Remember, you have choices regarding what interventions you opt-in to and when those interventions take place. Vaccines are no different. If you have questions about combining multiple vaccines in one visit, talk with your doctor or midwife.

Making a Decision

It is difficult to find a black-and-white answer to these tough questions, and the truth is that there is some grey area. We want assurance that any intervention is 100% safe, especially during pregnancy. This is where making informed decisions can be challenging. It is much easier to go with the flow of whatever your doctor or midwife recommends. It takes work to educate yourself on these topics, look at all the risks and benefits, and make a confident decision. Like any intervention, getting a vaccine should come with informed consent, which means you can opt out.

Vaccines are an challenging debate because you have to weigh the vaccine’s potential risks with the potential risks of the illness they are designed to protect you and your baby against. Ultimately, there is a risk no matter what you choose to do. Your job as a mother is to decide what risk you are comfortable with. Vaccines are not an all-or-nothing decision, and you may choose to get some vaccines and decline others.

Talk to Your Doctor or Midwife 

Hopefully, this article will provide a lot of evidence to help you decide whether the Tdap vaccine is right for you. Even if you are unsure whether you want the vaccine, you should have a basic understanding and confidence to have an educated conversation with your care provider. Please talk to your doctor or midwife about the Tdap vaccine and bring up any questions or concerns.

Thank you to the amazing companies that have supported this episode.