A vaccine contains a weakened or killed form of a disease-causing micro-organism that causes your body to produce antibodies. This provides immunity without actually inducing the disease. Vaccines are a very controversial topic. This episode introduces what vaccines are and gets into specifics on the Tdap vaccine during pregnancy. In addition to different types of vaccines, they contain many ingredients. These ingredients serve a particular function like increasing your immune response or as a byproduct of the processing. Tdap provides immunity for tetanus, diphtheria, and pertussis (whooping cough) and is recommended during pregnancy. Get the evidence-based risks and benefits of getting the Tdap vaccine during pregnancy so you can make an informed decision on whether it is right for you. 

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Article and Resources

Evaluating Vaccines

When I evaluate a vaccine or any medical intervention, I run through a series of questions and a lot of research. This article follows a similar format. Some of the questions I ask are: 

  • What are the risks of the illness the vaccine targets? 
  • What is the history of the vaccine? 
  • What are the ingredients in the vaccine? 
  • How effective is it? 
  • What are the risks and benefits? 
  • As you can imagine, this involves a lot of research. I also look at the particulars of the situation. With the Tdap vaccine, I would evaluate my current health status and the likelihood of exposure, including where I live, places I plan to travel to, the time of year, etc. 

The Controversy of Vaccines  

Vaccines are a very controversial and complex topic. Some professionals spend their lives dedicated to researching and studying vaccines and their safety. This article is an overview of the Tdap vaccine to give you a good base on available information. It is impossible to analyze every single study done because this is not the vaccine podcast, and there are many other essential topics I want to share with you. I have spent a significant number of hours, days, and weeks on this topic, and I hope that you find the information in this episode helpful as you are making choices about whether or not to get the Tdap vaccine during your pregnancy. 

Researching vaccines is incredibly challenging. It is easy to find yourself on a website that appears to be unbiased, only to discover an agenda, and it is firmly pro or con vaccine. This article aims to help you sift through all of the data out there to educate yourself and make an informed decision that is right for you. 

These are decisions that you should be making with your doctor or midwife. I cannot possibly cover every facet of this topic, and if you have further questions or concerns, I urge you to bring them up with your care provider. I am not for or against the Tdap vaccine. I firmly believe that you should be able to choose whether or not you receive any vaccine or medical intervention. If you listen to this podcast, you can make an informed decision and not one based on fear.  

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

In recent years, many people have raised questions about the accuracy of information from organizations like the CDC and the World Health Organization. There have also been questions about the influence pharmaceutical companies have over these organizations. As a data source, the CDC and the WHO have the most extensive centralized database for statistics on disease.

It is crucial to keep in mind that national and international health organizations are interested in protecting the population as a whole. Plus, their recommendations influence more specific policies by organizations like the American College of Obstetricians and Gynecologists, which directly impacts your care provider’s recommendation on topics like vaccines. Your main concern, understandably, is the safety and efficacy of a vaccine for you and your baby. Understanding the information informing your doctor or midwife will help you decide whether or not you want to get the Tdap vaccine and help arm you with the knowledge to have a conversation with your doctor or midwife.

That was long enough of a preface to this episode…let’s dive in. 

What is a Vaccine? 

Vaccines were first created in the 1790s with the smallpox vaccine. Although we have seen their growth increase as companies develop new vaccines, the science is not new. We need to lay some groundwork to understand how vaccines work and some of the language used when discussing the risks and benefits. 

Historically, a vaccine is created by taking a weakened or killed form of a disease-causing micro-organism and using microbes from the organism, its toxins, or one of its surface proteins. A medical professional gives a vaccine as an injection that causes your body to produce antibodies against that organism. This provides immunity without actually inducing the disease. This basically means that when you introduce a vaccine into your body, your body creates antibodies to fight it off. The number of micro-organisms in the vaccines shouldn’t be enough to give you the disease. If your body is ever exposed to the micro-organism again in the future, your body recognizes it and can fight it off. In some cases, your body develops immunity for your life after a vaccine. In other instances, immunity is only for a limited time, in which case you may need a booster shot. 

Different Types of Vaccines 

There are several types of vaccines. An inactivated vaccine uses micro-organisms that are no longer alive. In these vaccines, they are killed with heat, radiation, chemicals, or antibiotics. Examples of inactivated vaccines are the flu and pertussis (whooping cough) vaccines Boostrix. Attenuated vaccines are live vaccines. These can be cultured to have some of the properties disabled. These shouldn’t  cause the virus, or they are closely related to the virus enough to give you an immune response but not enough to make you sick. Toxoid vaccines are from toxic compounds that cause illness, like tetanus and diphtheria in the Tdap vaccine. Subunit vaccines are from the proteins of an organism. 

Ingredients in Vaccines 

Additional ingredients are added depending on the vaccine type, including adjuvants, stabilizers, and preservatives. An adjuvant, like aluminum, enhances the immune response of the antigen. Stabilizers increase the storage life of vaccines. Preservatives allow the use of multidose vials, where one vial contains multiple doses for multiple people. Doctors or nurses use new sterile needles when drawing out a dose from a multidose vial, and additional preservatives are needed to prevent the growth of bacteria or fungi. 

Antibiotics may be added to vaccines to prevent the growth of bacteria. 

The virus for many flu shots is grown in chicken eggs, and trace amounts of egg protein are in the final product. 

Manufacturers use formaldehyde to inactivate bacterial products in toxoids. It can also inactivate unwanted viruses or bacteria that can contaminate the vaccine during production. Formaldehyde is also used as a preservative, as is the case in the Boostrix Tdap vaccine.  

MSG (monosodium glutamate) and 2-phenoxyethanol are used as stabilizers for heat, light, humidity or acidity, and as a preservative. 

Thimerosal is an antimicrobial that contains mercury and is added to multidose vaccines to prevent contamination and growth of potentially harmful bacteria. Due to the controversy surrounding thimerosal, it is no longer in most vaccines, but it is still in multidose flu shots.  

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. 


There are a few different classifications of immunity. Individual immunity is when individuals become immune when they receive a vaccine. Passive immunity happens when you receive a vaccine and then pass antibodies to your baby either through the placenta in utero or in colostrum or breastmilk. Herd immunity occurs when a large percentage of the population is vaccinated. In effect, it protects the whole population, especially those who cannot receive vaccines. Herd immunity is an essential part of eradicating a disease, and this only applies to contagious diseases. One of the most crucial aspects of herd immunity is protecting people who cannot develop immunity. This includes children who are too young for a vaccine and people who cannot receive a vaccine because of a medical reason. Someone with a compromised immune system or who has had an allergic or adverse reaction to a vaccine may not be able to get it. These individuals rely on the immunity of the population as a whole to protect them. 

Tetanus, Diphtheria, and Pertussis 

The Tdap vaccine protects you against three different illnesses. Tetanus, diphtheria, and pertussis. 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. It 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 cause death. 2017 is the most recent year data available from the CDC, and they report 33 infections, with a total of two deaths. 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.

Diphtheria is extremely rare in the United States today. From 1996-2017 there were only 13 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 23,000 cases were reported in 2019 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. 

The main aim of the Tdap vaccine is pertussis, also known as whooping cough, and is a highly contagious respiratory tract infection. In 2017 there were 18,975 cases of pertussis reported in the U.S. Airborne bacteria causes 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. From 2012 through 2017, 66.7% of all pertussis-related deaths reported to the CDC were infants less than two months of age.

The Tdap Vaccine During Pregnancy 

The Tdap vaccine is recommended for all pregnant women during each pregnancy. This is an inactivated vaccine, and it doesn’t contain any live bacteria. It is given via intramuscular injection in your upper arm in the third trimester, from 27-36 weeks.

The first trimester is seen as the most vulnerable for your baby having an acute inflammatory response, teratogenic (anything that causes a defect in a developing baby) exposure, or developing a congenital abnormality. This is one of the reasons that it is recommended that you do not receive the Tdap vaccine until later in your pregnancy. 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.

Combining Tdap and Other Vaccines 

An additional consideration with the timing of the Tdap vaccine is whether to get it at the same time as other vaccines.

When COVID-19 vaccines first became available, the CDC recommended waiting 14 days between the COVID-19 vaccine and any other vaccine as a precautionary measure. The CDC has since changed their recommendation and states that you can receive the COVID-19 vaccine simultaneously as other vaccinations. The CDC does say, “it is not known if the reactogenicity of COVID-19 vaccines is increased with coadministration, including with other vaccines known to be more reactogenic, such as adjuvanted vaccines.”

According to CDC, you can get Tdap and flu shots at the same time. 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. If you plan to get both the Tdap and flu shots during pregnancy, talk with your doctor or midwife about the timing.

Official Recommendations 

The American College of Obstetricians and Gynecologists supports the recommendation that all expecting mothers receive the Tdap vaccine. They state that pregnant women should be counseled that the administration of the Tdap vaccine during each pregnancy is safe. It is important to make sure that each newborn receives the highest possible protection against pertussis at birth. The American College of Nurse-Midwives also recommends the Tdap vaccine during pregnancy.

Why is the Tdap Vaccine Recommended During Pregnancy? 

It may seem strange that this vaccine is recommended during pregnancy because two of the three illnesses it protects against are nearly non-existent. The main reason it is recommended is for pertussis and for the passive immunity your baby receives. A vaccine for pertussis alone is not commercially available for use in pregnant women. For this reason, countries recommending a pertussis vaccine during pregnancy use combined tetanus, diphtheria, and acellular pertussis vaccine. 

The younger a baby is when they get whooping cough, the more likely they will need to be treated in the hospital. The CDC publishes statistics on the cases of pertussis every year. 2019 is the most recent year data is available. 40.9% of babies under six months who had whooping cough were hospitalized. There were a total of 18,617 reported cases in the U.S. 12% of these were babies under one year of age, and just over half of those were admitted to a hospital. In 2019 there were seven reported pertussis deaths, and four of those were in children under one year old.

Protecting Your Baby 

Keep in mind that your baby is born without much of an immune system. The passive immunity they receive when you get the vaccine should protect them until they are old enough to receive the vaccine, around two months. 

The American Academy of Pediatrics also supports the Tdap vaccine during pregnancy. They cite a 2017 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. 

The American College of Obstetricians and Gynecologists is clear in their recommendation for the Tdap vaccine to protect infants through passive immunity. They note that the window between birth and two months, when the pertussis vaccine is recommended for infants, is a window of significant vulnerability for newborns, many of whom contract serious pertussis infections from family members and caregivers, especially the mother, or older siblings, or both. As a side note, the pertussis vaccine for children is Dtap, which differs from the Tdap vaccine for adults. ACOG goes even further to recommend family members and caregivers who previously have not received the Tdap vaccine and who have or anticipate having close contact with an infant younger than 12 months should receive a single dose of Tdap to protect against pertussis. 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.  

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

Pregnancy category C, Animal reproduction studies have not been conducted with the Adacel vaccine. It is also unknown whether the Adacel vaccine can cause fetal harm when administered to a pregnant woman or affect reproduction capacity. Adacel vaccine should be given to a pregnant woman only if clearly needed.  

Adacel vaccine does not contain a preservative. 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).  

Boostrix GlaxoSmithKline

Pregnancy Category B. A toxicity study in female rats at a dose approximately 40 times the human dose (on an mL/kg basis) revealed no evidence of harm to the fetus due to BOOSTRIX.

Each 0.5-mL dose contains aluminum hydroxide as adjuvant (not more than 0.39 mg aluminum by assay), 4.4 mg of sodium chloride, ≤100 mcg of residual formaldehyde, and ≤100 mcg of polysorbate 80 (Tween 80). 

Evidence on the Safety of the Tdap Vaccine During Pregnancy 

In recent years, there have been several studies that have looked at the safety of the Tdap vaccine during pregnancy. An observational study in California between 2010 and 2012 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. 

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 of a skeptic 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. 

Making a Decision

It is difficult to find a black and white answer to these tough questions, and the truth is that it is not black and white. I know we want assurance that any intervention is 100% safe, especially during pregnancy, and it just isn’t. This is where making informed decisions can be challenging. It is much easier to just go with the flow as to whatever your doctor or midwife recommends. It takes work to educate yourself on these topics, look at all of the risks and benefits, and make a decision you feel confident in. Like any intervention, getting a vaccine should come with informed consent, which means you should be able to opt-out.

Vaccines are an interesting 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 risk no matter what you choose to do. You need to decide for yourself what you are comfortable with. 

Talk to Your Doctor or Midwife 

You have a lot of evidence after reading this article, and hopefully, you can decide whether the Tdap vaccine is right for you. Even if you are unsure which way you want to go, you should have a basic understanding and some confidence that you can have a conversation with your care provider about this if you have more questions. Please talk to your doctor or midwife about the Tdap vaccine. If you have concerns, bring them up. If you want to consider a specific brand of vaccine, speak up. Your care provider is your trusted partner during your pregnancy, and their opinion is worth hearing. Please discuss any questions, no matter how small or silly they may seem. 

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

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