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A vaccine is created by taking 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 is an introduction to what vaccines are and gets into specifics on the Tdap vaccine during pregnancy. In addition to different types of vaccines, there are many ingredients that can be included in vaccines. These ingredients serve a particular function like increasing your immune response or as a byproduct of the processing. Tdap is one of two vaccines recommended during pregnancy that provides immunity for tetanus, diphtheria, and pertussis (whooping cough). Get the benefits and risks 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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Tdap is short for tetanus, diphtheria, and pertussis. Pertussis is commonly known as whooping cough. In addition to the flu shot, this is the other vaccine that is routinely recommended during pregnancy.

When I am evaluating 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 ingredients are included 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 the status of my current health, the likelihood of exposure which would include where I live or places I am planning to travel to, the time of year, etc. You get the point. There are a lot of questions and this involves lots of research.

The Controversy of Vaccines

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

Researching vaccines is especially challenging. It is easy to find yourself on a website that appears to be unbiased, only to discover there is an agenda and it is strongly pro or con vaccine. My agenda with this article is 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. While I am not for or against the Tdap vaccine, I strongly believe that you should be able to make the choice as to whether or not you receive any vaccine, or medical intervention. I know if you are reading this article you are making an informed decision, and not one based on fear.

What is a Vaccine?

Vaccines were first created in the 1790s with the smallpox vaccine. They are not a new invention, although we have seen their growth increase as new vaccines are being created. In order to understand how vaccines work and some of the language used when discussing the risks and benefits we need to lay some foundation down.

A vaccine is created by taking a weakened or killed form of a disease causing micro-organism and using either microbes from the organism, its toxins, or one of its surface proteins. This is given as an injection that causes your body to produce antibodies against that organism and provide immunity without actually inducing the disease. What this basically means is that when a vaccine is introduced into your body, your body creates antibodies to fight it off. The amount of the micro-organism 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 is able to fight it off. In some cases, your body develops immunity for your lifetime after a vaccine. In other cases, 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 the pertussis (whooping cough) vaccine Boostrix. Attenuated vaccines are live vaccines. These can be cultured to have some of the properties disabled. These shouldn’t actually 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 made from toxic compounds that cause illness, like tetanus and diphtheria in the Tdap vaccine. Subunit vaccines are made from proteins of an organism.

Ingredients in Vaccines

Depending on the type of vaccine additional ingredients are added which can include adjuvants, stabilizers, and preservatives. An adjuvant enhances the immune response of the antigen. An example of this would be aluminum which is commonly added to vaccines. Stabilizers increase the storage life of vaccine so it can be safely stored from the time it is manufactured until it is administered. Preservatives allow the use of multidose vials, where one vial contains multiple doses for multiple people. New sterile needles are always used 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.

Egg protein can be included, as in many flu shots because the virus is grown using chicken eggs.

Formaldehyde may be used 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 multi-dose vaccines to prevent contamination and growth of potentially harmful bacteria. Due to the controversy surrounding thimerosal it has been removed from most vaccines, but it is still in multidose flu shots.

That is a lot of ingredients that can be included in vaccines. I am not going to do a deep dive into the safety of each of these. I am sure you have more important things to do than fall asleep reading this article. This article will dive deep into the safety of the Tdap vaccine and talk about the specific ingredients included in your options for that.


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 the antibodies you produce are passed to your baby either through the placenta in utero or in colostrum. 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 important aspects of herd immunity is that it protects 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.

The Role of the Centers for Disease Control

I am going to talk a lot about CDC guidelines because this is what your care provider is likely recommending. The CDC is interested in protecting the whole population. Your concern, understandably, is likely you and your baby. We are going to dig deep into that, and beyond the benefits of the population as a whole.

Tetanus, Diphtheria, and Pertussis

The Tdap vaccine protects you against 3 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 anerobic environment, which means there is not oxygen. We often think of tetanus coming from stepping on a rusty nail. In this case the sharp nail creates a deep puncture wound, a great anerobic environment, and the nail being rusty is dirty theoretically contaminated with this bacteria. It causes painful muscle tightening and stiffness, usually all over the body. It can lead to tightening of muscles in the head and neck so you can’t open your mouth, swallow, or sometimes 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. 2015 is the most recent year data is available from the CDC  and they report 29 infections, with a total of 2 deaths. In other parts of the world tetanus is more common and the World Health Organization estimated that in 2015 34,019 newborns died from neonatal tetanus. This is the same year we had only 29 cases reported in the U.S. for all ages.

Diphtheria is extremely rare in the United States today. Over the last 50 years there have only been 5 reported cases in the U.S. This was a much bigger issue prior to the introduction of vaccines. In other parts of the world it is more common and 7,100 cases were reported in 2016 to the WHO. Diphtheria can cause a thick coating to form in the back of the throat which can lead to breathing problems, heart failure, paralysis, and death.

The main aim of the Tdap vaccine is pertussis. This is also known as whooping cough and is a highly contagious respiratory tract infection. This is caused by bacteria that is airborne when an infected person coughs or sneezes. Within 10 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. A thick mucus accumulates inside your airways, causing uncontrollable coughing. When an infant has pertussis they may not cough at all, they may just struggle to breathe or temporarily stop breathing.

The Tdap Vaccine During Pregnancy

The Tdap vaccine is recommended for all pregnant women during each pregnancy. It is given via an intramuscular injection in your upper arm in the third trimester, which runs from 27-36 weeks. The antibodies your body creates are highest 2 weeks after you receive the vaccine. This is an inactivated vaccine, and it doesn’t contain any live bacteria. 

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.

Combining the Flu and Tdap Vaccines

An additional consideration with the timing of the Tdap vaccine is whether to get it at the same time as the flu vaccine. According to CDC, you can get Tdap and flu shot at the same time. In one of the clinical trials disclosed in the insert for the Tdap vaccine Adacel they found when the Adacel vaccine was administered at the same time 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 helps you develop immunity for pertussis. If you are planning to get both the Tdap and the flu shot during your pregnancy talk with your doctor or midwife about the timing of those two vaccines.

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 and important to make sure that each newborn receives the highest possible protection against pertussis at birth.

Why is the Tdap Vaccine Recommended During Pregnancy?

It may seem strange that this vaccine is recommended during pregnancy because 2 of the 3 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 a combined tetanus, diphtheria, and acellular pertussis vaccine.

The younger a baby is when they get whooping cough, the more likely it is that they will need to be treated in the hospital. Around 42% of babies under 6 months who have whooping cough end up in the hospital. The CDC keeps statistics on the cases of pertussis every year. In 2018 there were a total of 13,439 reported cases in the U.S. This is down from nearly 19,000 in 2017. 12.5% of these were babies under one year of age and over half of those were admitted to a hospital. The CDC extrapolates these numbers to estimate the number of deaths per 100,000 cases and this is estimated to be 4 deaths of children under one year of age per 100,000, and 6 deaths of those over one year. In recent years there have been much higher cases of pertussis and outbreaks which really sparked pressure from the medical community to get this vaccine during pregnancy.

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, which is around 2 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 pretty clear in their recommendation for the Tdap vaccine to protect infants through passive immunity. They note that the window between birth and 2 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 partners, family members, and infant caregivers should be offered the Tdap vaccine if they have not previously been vaccinated. Ideally, all family members should be vaccinated at least 2 weeks before coming in contact with the newborn.

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 who will be spending time around your new baby get the vaccine.

Comparing Your Vaccine Options

There are two manufacturers that make the Tdap vaccine and 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 Adacel vaccine. It is also not known whether Adacel vaccine can cause fetal harm when administered to a pregnant woman or can 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 made by GlaxoSmithKline

Pregnancy Category B, toxicity study has been performed in female rats at a dose approximately 40 times the human dose (on a mL/kg basis) and 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

There have been several studies in recent years that have looked at the safety of the Tdap vaccine during pregnancy. An observational study done 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 who received the Tdap shot and 5.5% in the group that did not.

There is a systematic review that 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. Plus, I cannot share them publicly to give you full access after I have purchased them. I am careful to read full studies and not go off of abstracts or summaries and this 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 funded this review. In the end I felt like I had to purchase the study and read through it to honor my commitment to you to dig deep into the research.

The conclusion of this study states that evidence suggests that antenatal combined 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. Not to be skeptical, but it is rare research funded by a pharmaceutical company is published if it finds evidence that could be damaging to the company who funded 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, which is 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 be the result of the different methods used to identify adverse events, definitions, and variability expected from small sample sizes. What is interesting is that the reporting of these side effects in the clinical trials for both Adacel and Boostrix tended to be at the upper end, or over the rates found in these studies.

This review addresses a great point that we should keep in mind when looking at studies during pregnancy. They note that observational research has been the mainstay of evidence available for women vaccinated during pregnancy. They go on to 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 is a result of the comparative cost, ethical considerations, and underrepresentation of pregnant women in clinical trials.

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 a lot easier to just go with the flow as to whatever your doctor or midwife recommends. It takes work to educate yourself on these topics and look at all of the risks and benefits and make a decision that you feel confident in.

Vaccines are an interesting debate because you have to weigh the potential risks of the vaccine 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.

You have a lot of evidence after reading this article. Hopefully you can decide whether the Tdap vaccine is right for you. Even if you are not sure which way you want to go, you should have a basic understanding and confidence that you can have a conversation with your care provider about this if you have more questions. As with anything pregnancy related this should be an informed consent decision. You do have the ability to opt out or opt in to this vaccine.

Talk to Your Doctor or Midwife

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.


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