The severity and spread of COVID-19 drove demand to create vaccines and get them to the public in record time. In the United States, the FDA has approved three vaccines; two of them are still under an emergency use authorization. We know from real-world data that pregnancy can increase your risks for severe illness from COVID-19. Despite pregnancy increasing COVID-19 risks, clinical trials did not include pregnant participants. Studies are beginning to focus on these vaccines in pregnancy, and researchers are releasing more data on vaccinated pregnant women. While we lack long-term data, ACOG and the CDC recommend that pregnant women get vaccinated for COVID-19. This episode dives into the available evidence on the safety and efficacy of COVID-19 vaccines during pregnancy so you can make an informed decision on whether to get the vaccine.

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Article and Resources

For all of the episodes, information, and research on COVID-19 see this page.

Additional COVID-19 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? 

I also look at the particulars of the situation. With the COVID-19 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. 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, especially when it comes to the COVID-19 vaccine. Some professionals spend their lives dedicated to researching and studying vaccines and their safety. This article is an overview of the COVID-19 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 weeks on this topic, and I hope that you find the information in this episode helpful as you make choices about whether or not to get the COVID-19 vaccine during your pregnancy. 

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 COVID-19 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

Since the COVID-19 pandemic began, 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. In hindsight, it is clear there was mishandling of policies relating to things like testing and mask-wearing. As a data source, the CDC and the WHO have the most extensive centralized database for statistics on disease.

It is essential 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 COVID-19 vaccine and help arm you with the knowledge to have a conversation with your doctor or midwife.

The General Consensus, Censorship, and Misinformation

There is no doubt that we have not seen such an aggressive campaign for a vaccine before. This has become highly controversial, especially in the United States, where the vaccine debate has morphed into a political issue and a topic tied into personal freedom. The goal of national health organizations and governments is to protect the largest portion of the population as possible. It is clear they believe vaccines are the best way to do that.

Tech companies and the media have censored many individuals who have spoken out against the vaccine. Content creators, scientists, doctors have had YouTube videos removed, social media posts taken down, and web pages buried. There is a massive campaign to eliminate misinformation about COVID-19 and the vaccines. In fighting misinformation, there will be some portion of accurate information that is also lost.

There are anecdotal stories from people who got a COVID-19 vaccine and had an adverse reaction. It can be really scary not to have all the information you want to make an informed medical decision. This is especially true when you are pregnant, and you also have to take your baby’s health and well-being into consideration. Many people are deciding to opt-in or out of the COVID-19 vaccine based on fear. Your job is to make the best-informed decision you can with the information you have available.

Recommended Vaccines During Pregnancy

Before COVID-19, only the Tdap and flu vaccines were routinely recommended during pregnancy. Expecting mothers are underrepresented in clinical research. This underrepresentation is partly due to the complexity of pregnancy and the vulnerability of developing babies. As COVID-19 has continued to impact pregnant mothers worldwide, there has been more attention to the need to include expecting mothers in clinical research.


COVID-19 is a disease caused by the SARS-CoV-2 respiratory virus. This novel virus emerged towards the end of 2019 and has continued to spread globally. According to Johns Hopkins Coronavirus Research Center, as of October 19, 2021, there have been over 241 million cases of COVID-19 worldwide and over 4.9 million deaths.

The SARS-CoV-2 virus is transmitted primarily from air droplets. When an infected person coughs, breathes, or sneezes, the virus can travel in aerosols in the air, which could be breathed in or land on a surface. 

Different Variants of COVID-19

SARS-CoV-2, like any virus, evolves and mutates over time. These mutations create different variants of the original virus. As COVID-19 has continued to spread, we have seen additional variants of the virus. The variants can affect how transmissible the virus is and the severity of symptoms.

As more data becomes available, vaccines may need to be updated to protect against different variants. The World Health Organization states that COVID-19 vaccines currently in development or approved are expected to provide at least some protection against new virus variants, including the delta variant.

COVID-19 Symptoms

The main symptoms of this virus are fever, cough, and shortness of breath. These could appear anywhere between 2-14 days after exposure to the virus. Emergency warning signs include difficulty breathing or shortness of breath, persistent pain or pressure in the chest, confusion or inability to arouse, and bluish lips or face. If you have any symptoms, you want to reach out to your doctor or midwife right away. You want to be proactive as much as possible and not wait.

It is estimated that around 25% of cases are asymptomatic, which means you have no noticeable symptoms. Individuals who are positive for SARS-CoV-2 but asymptomatic can still spread the virus to others.

Defining Mild, Moderate, & Severe Symptoms

Symptoms of COVID-19 are classified as mild, moderate, and severe. Mild means that there is no shortness of breath, difficulty breathing, or abnormal chest imaging. Moderate cases involve evidence of lower respiratory disease and abnormal chest imaging. Severe cases have decreased oxygen saturation. Critical illness includes individuals with respiratory failure, septic shock, and organ failure. The most severe cases can result in intensive care admission, mechanical ventilation, or death. Many underlying conditions can put you at a higher risk for severe COVID-19, including diabetes and cardiovascular disease. Even pregnancy can increase your risk for severe symptoms of COVID-19.

COVID-19 During Pregnancy 

According to the CDC, although the overall risk of severe illness is low, pregnant people are at an increased risk for severe illness from COVID-19 compared to non-pregnant people. Additionally, pregnant people with COVID-19 might be at increased risk of adverse pregnancy outcomes, such as preterm birth, compared with pregnant women without COVID-19.

Another thing to keep in mind is that if you test positive for COVID-19, it may impact your birth. Some hospitals and birth centers are not allowing partners present for expecting mothers who are positive for COVID-19.

Birth centers may require you to transfer to a hospital if you are positive for COVID-19. If you have any questions about how a positive test could impact your prenatal care or birth, please talk to your doctor or midwife.

The COVID-19 Vaccine 

Historically vaccines have taken a decade or longer to develop and get to market. Due to the severity and spread of COVID-19, there was a massive demand to get vaccines developed as quickly as possible. Pharmaceutical companies utilized government funding, previous research on SARS and MERS, and vaccine technology that is quick to produce to get vaccines to the public in under a year.

Vaccine Trials

Vaccines are required to go through vigorous testing and oversight before approval for use. While there has been skepticism about these vaccines due to the quick approval process, they still underwent the typical development stages.

Preclinical trials may involve animal testing as drug manufacturers dial in the vaccine and dosage. Once a trial vaccine is created, the manufacturer tests it during Phase I in small groups of healthy people. Phase II expands the testing group to more people with characteristics similar to those for whom the vaccine is intended. In Phase III, the vaccine is given to thousands of people and further tested for efficacy and safety.

Two of the three vaccines currently approved in the United States have emergency use authorization from FDA. When specific criteria are met, the FDA can issue an emergency use authorization for a drug, vaccine, or treatment during a public health emergency. Those criteria include that the FDA deems the benefits outweigh the risks and that there are no adequate, approved, and available alternatives. There has been some controversy about whether there are no alternatives. The FDA has stuck by its position that these vaccines meet the requirements for emergency use approval.

Emergency use makes the approval process shorter and less involved than required for full FDA approval. After emergency use approval, the FDA continues to monitor vaccine safety. The Vaccine Adverse Event Reporting System (VAERS) collects and analyzes reports of adverse reactions from vaccines.

How COVID-19 Vaccines Work 

In the past, all vaccines worked by introducing some part of a bacteria, virus, or pathogen into your body to trigger an immune response. Some of the vaccines developed for COVID-19 use a different approach.


Some of the vaccines available are mRNA vaccines. mRNA stands for messenger ribonucleic acid. mRNA carries genetic code from DNA for protein synthesis. Instead of using a bacteria, virus, or pathogen, mRNA vaccines teach our cells how to make a protein that triggers an immune response and produces antibodies. COVID-19 has spike proteins that help it invade cells. mRNA vaccines give instructions for our cells to make a piece of the spike protein. This piece of the spike protein does not cause COVID-19. This protein is recognized by your immune system and allows you to produce an antibody response. The result is that you have some immunity since your body can recognize and hopefully fight off COVID-19 in the future. mRNA vaccines never enter the nucleus of a cell and cannot cause genetic changes to your DNA.

A huge benefit of using mRNA technology is these vaccines can be created more rapidly than other methods. This is one reason we have developed COVID-19 vaccines more quickly than other vaccines in the past.

mRNA technology is exciting, and hopefully, this will be a huge success story and pave the way for how all future vaccines are produced. mRNA vaccines have been studied for decades, but none have ever been approved for use until now. One risk is that this is a relatively new technology, and we lack long-term data on safety.

Viral Vector Vaccines

Another newer technology utilized in some COVID-19 vaccines is a viral vector. These vaccines use a modified version of a different virus to deliver instructions to our cells to produce a spike protein for COVID-19.

According to the CDC, vaccines that use the same viral vector have been given to pregnant people in all trimesters of pregnancy, including in a large-scale Ebola vaccination trial. No adverse pregnancy-related outcomes, including adverse outcomes that affected the infant, were associated with vaccination in these trials.

COVID-19 Vaccines During Pregnancy

The American College of Obstetricians and Gynecologists practice advisory updated 10/01/2021 recommends that all eligible persons greater than age 12 years, including pregnant and lactating individuals, receive a COVID-19 vaccine or vaccine series. For patients who do not receive the vaccine, the discussion should be documented in the patient’s medical record. During subsequent office visits, obstetrician-gynecologists should address ongoing questions and concerns and offer vaccination again. This is a stronger recommendation than ACOG issued earlier this year, stating that COVID-19 vaccines should not be withheld from pregnant individuals and that individuals considering a COVID-19 vaccine should have access to available information about the safety and efficacy of the vaccine, including information about data that is not available. 

The World Health Organization recommends the use of the COVID-19 vaccine in pregnant women when the benefits of vaccination to the pregnant woman outweigh the potential risks. To help pregnant women make this assessment, they should be provided with information about the risks of COVID-19 in pregnancy, the likely benefits of vaccination in the local epidemiological context, and the current limitations of safety data in pregnant women. Earlier this year, the WHO only recommended the COVID-19 vaccine for pregnant women at high risk of exposure or who have comorbidities that add to their risk.

Developing Vaccine Antibodies During Pregnancy

Once you get the COVID-19 vaccine, it takes your body about two weeks to develop antibodies. Some vaccines require multiple doses to ensure your body produces enough antibodies for adequate protection from the virus.

Passing antibodies to your baby in utero or via breastmilk is called passive immunity. The goal when you get a vaccine during pregnancy is to protect both you and your baby. Part of the push to get the COVID-19, Tdap, or flu vaccines during pregnancy is to give your baby immunity. Currently, COVID-19 vaccines are not approved for children under 12. Your child cannot get a Tdap shot until two months old or an influenza vaccine until six months.

In one study that included 84 pregnant women, COVID-19 vaccine-generated antibodies were present in all umbilical cord blood samples. Another study of 36 mother and newborn pairs also found antibodies in cord blood following vaccination during pregnancy. Both of these studies included participants that received an mRNA vaccine.

Passing Antibodies in Breastmilk

After your baby is born, you also continue to pass antibodies to them through your breastmilk. In the first study mentioned above, breastmilk samples from 31 lactating mothers who received a COVID-19  vaccine showed vaccine-generated antibodies. I cannot stress enough the importance of breastfeeding, especially during the first few months of your baby’s life. This is whether or not you decide to get the COVID-19 vaccine. Even if your baby is getting formula and every meal isn’t breast milk, those antibodies you pass when you breastfeed are amazing. Breastfeeding will significantly improve your newborn’s immune system and help to keep them healthier. 

Antibody Unknowns

We know you create antibodies and can pass them to your baby after a vaccine. What about antibodies from a natural COVID-19 infection? A study examined three groups of people and their antibody levels. It included a group of people who had a COVID-19 infection, a group who received an mRNA vaccine, and a group who had both natural infection and a vaccine. All three groups had antibodies. Those who had COVID-19 had more protection against variants. The group that had both a COVID-19 infection and a vaccine had the best protection.

Currently, the CDC does not recommend antibody testing to assess the need for vaccination or proof of immunity. There is still a lot we do not know about how long you produce antibodies after an infection or a vaccine and how protective those antibodies are. You can get tested for antibodies, but there is no universal threshold to prove you have immunity from COVID-19 or variants.

Hopefully, we will see more research in the future. The National Institute of Health has begun a study that will evaluate the immune response and the transfer of antibodies during pregnancy and breastfeeding.

One study showed that the sex of a baby in utero can impact how a mother transfers antibodies during pregnancy. We know that SARS-CoV-2 affects males disproportionately, and the same may be true for babies in utero. This research showed a lower antibody transfer to male babies. This is one example of an endless list of questions about antibodies.

Booster Shots

While there are unknowns about antibodies from the vaccines, we do know they decrease over time. As a result, booster shots have now rolled out. ACOG recommends that pregnant people, including pregnant health care workers, receive a booster dose of the Pfizer-BioNTech COVID-19 vaccine at least six months following the completion of their initial Pfizer-BioNTech COVID-19 vaccine series. Depending on the timing of your vaccines, your care provider may recommend a booster during your pregnancy.

On October 21, 2021, the CDC endorsed booster shots for Moderna and Johnson and Johnson. Boosters are recommended six months after the Moderna or Pfizer series or two months after the Johnson and Johnson vaccine. The CDC goes on to recommend that you can get any booster, regardless of the brand of your initial vaccine. From the data available now, the risks and side effects of the booster shot are the same as the other vaccine doses. We can expect ACOG to update their recommendation to match the CDC.

Different Vaccines Available

There are three different vaccines available in the United States. ACOG states there is currently no preference for using one COVID-19 vaccine over another except for 12-17-year-olds who are only eligible for the Pfizer-BioNTech vaccine. There are differences in the safety and efficacy of these vaccines. If you prefer one brand over another, you can seek out that vaccine. The CDC has a vaccine finder tool that allows you to search based on vaccine brand. Availability may vary based on the doctor of the facility where you are vaccinated.

There is a link to the manufacturer’s fact sheet for each vaccine, which contains a lot of data about the vaccine and the clinical trials. One vaccine from Pfizer has full approval, and the other two from Moderna and Johnson and Johnson are currently approved are through the FDA’s EUA (emergency authorization use). For all vaccines, manufacturers state that if you are pregnant or breastfeeding, discuss your options with your healthcare provider.

Comirnaty Pfizer-BioNTech

  • Full Approval: August 2021 in the U.S. for individuals 16 years of age and older
  • EUA Approval: May 2021 in the U.S. for individuals 12 through 15 years of age
  • Type of vaccine: mRNA
  • Doses: two doses, three weeks apart
  • Clinical Trials: Two clinical trials involving 44,600 participants, of which 21,918 received at least one Pfizer vaccine dose.
  • Vaccine efficacy: 95%
  • Adverse reactions: pain at the injection site 84.1%, fatigue 62.9%, headache 55.1%, myalgia (muscle pain) 38.3%, arthralgia (joint pain) 23.6%, chills 31.9%, nausea/vomiting 1.1%, lymph node swelling/tenderness 0.3%, fever 14.2%, swelling at the injection site 10.5%, erythema (redness) at the injection site 9.5%, and malaise (generally feeling unwell) 0.5%. These figures include adverse reactions for all doses. All adverse reactions, except pain at the injection site, increased from first to second.
  • Serious Adverse Events: Appendicitis was reported as a serious adverse event for 12 participants, numerically higher in the vaccine group, eight vaccine participants, and four placebo participants. Currently, available information is insufficient to determine a causal relationship with the vaccine. Bell’s palsy (facial paralysis) was reported by four participants in the Pfizer-BioNTech COVID-19 Vaccine group. No cases of Bell’s palsy were reported in the placebo group. Currently, available information is insufficient to determine a causal relationship with the vaccine.
  • Ingredients: Vaccine contains 30 mcg of a nucleoside-modified messenger RNA (modRNA) encoding the viral spike (S) glycoprotein of SARS-CoV-2. Each dose of the Pfizer-BioNTech COVID-19 Vaccine also includes the following ingredients: lipids (0.43 mg (4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate), 0.05 mg 2[(polyethylene glycol)-2000]- N,N-ditetradecylacetamide, 0.09 mg 1,2-distearoyl-sn-glycero-3-phosphocholine, and 0.2 mg cholesterol), 0.01 mg potassium chloride, 0.01 mg monobasic potassium phosphate, 0.36 mg sodium chloride, 0.07 mg dibasic sodium phosphate dihydrate, and 6 mg sucrose. The diluent (0.9% Sodium Chloride Injection, USP) contributes an additional 2.16 mg sodium chloride per dose. The Pfizer COVID-19 Vaccine does not contain a preservative. The vial stoppers are not made with natural rubber latex.
  • Research relating to pregnancy: In a reproductive and developmental toxicity study, 0.06 mL of a vaccine formulation containing the same quantity of nucleoside-modified messenger ribonucleic acid (mRNA) (30 mcg) and other ingredients included in a single human dose of Pfizer-BioNTech COVID-19 Vaccine was administered to female rats by the intramuscular route on four occasions: 21 and 14 days prior to mating, and on gestation days 9 and 20. No vaccine-related adverse effects on female fertility, fetal development, or postnatal development were reported in the study.


  • EUA Approval: December 2020 in the U.S. for individuals 18 years of age and older
  • Type of vaccine: mRNA
  • Doses: two doses, one month apart
  • Clinical Trials: Three clinical trials involving 30,351 participants, of which 15,419 received at least one dose of the Moderna vaccine.
  • Vaccine efficacy: 94.1%
  • Adverse reactions: pain at the injection site 92.0%, fatigue 70.0%, headache 64.7%, myalgia (muscle pain) 61.5%, arthralgia (joint pain) 46.4%, chills 45.4%, nausea/vomiting 23.0%, axillary (armpit) swelling/tenderness 19.8%, fever 15.5%, swelling at the injection site 14.7%, and erythema (redness) at the injection site 10.0%. These figures include adverse reactions for all doses. All adverse reactions increased from the first to the second dose.
  • Serious Adverse Events: There are three serious adverse events of facial swelling in vaccine recipients with a history of injection of dermatological fillers. The swelling was likely related to vaccination.
  • There were three reports of Bell’s palsy in the Moderna COVID-19 Vaccine group (one of which was a serious adverse event) and one in the placebo group. Currently, available information on Bell’s palsy is insufficient to determine a causal relationship with the vaccine.
  • Ingredients: a total lipid content of 1.93 mg (SM-102, polyethylene glycol [PEG] 2000 dimyristoyl glycerol [DMG], cholesterol, and 1,2-distearoyl-sn-glycero-3-phosphocholine [DSPC]), 0.31 mg tromethamine, 1.18 mg tromethamine hydrochloride, 0.043 mg acetic acid, 0.12 mg sodium acetate, and 43.5 mg sucrose. Moderna COVID-19 Vaccine does not contain a preservative and vial stoppers are latex-free.
  • Cases of severe COVID-19: no cases of severe COVID-19 were reported in the Moderna COVID-19 Vaccine group compared with 30 cases reported in the placebo group.
  • Research relating to pregnancy: In a developmental toxicity study, 0.2 mL of a vaccine formulation containing the same quantity of nucleoside-modified messenger ribonucleic acid (mRNA) (100 mcg) and other ingredients included in a single human dose of Moderna COVID-19 Vaccine was administered to female rats by the intramuscular route on four occasions: 28 and 14 days prior to mating, and on gestation days 1 and 13. No vaccine-related adverse effects on female fertility, fetal development, or postnatal development were reported in the study.

Johnson & Johnson’s Janssen

  • EUA Approval: February 2021 in the U.S. for individuals 18 years of age and older
  • Type of vaccine: viral vector
  • Doses: one dose
  • Clinical Trials: One clinical trial involving 44,325 participants, 21,895 received at least one dose of the Janssen vaccine.
  • Vaccine efficacy: 66.1% Based on 39,321 participants, 19,630 that received the vaccine
  • Adverse reactions: Safety was analyzed from a subset of 6,736 participants of the total trial participants, 3,356 who received the vaccine. Pain at the injection site 48.6%, fatigue 38.2%, headache 38.9%, myalgia (muscle pain) 33.2%, nausea/vomiting 14.2%, fever 9.0%, swelling at the injection site 5.3%, and erythema (redness) at the injection site 7.3%.
  • Serious Adverse Events: One report of severe pain in the injected arm, not responsive to analgesics, with immediate onset at the time of vaccination, ongoing 74 days following vaccination, likely related to the vaccine. Six events of deep vein thrombosis in the vaccination group vs. 2 in the placebo group. 4 cases of pulmonary embolism vs. one event in the placebo group. One event of transverse sinus thrombosis. There were four seizures in the vaccine group vs. 1 in the placebo group. Six events of tinnitus in the vaccine group. For these events, a causal relationship with the Janssen COVID-19 vaccine cannot be determined.
  • Ingredients: n 5×1010 virus particles (VP) and the following inactive ingredients: citric acid monohydrate (0.14 mg), trisodium citrate dihydrate (2.02 mg), ethanol (2.04 mg), 2-hydroxypropyl-β-cyclodextrin (HBCD) (25.50 mg), polysorbate-80 (0.16 mg), sodium chloride (2.19 mg). Each dose may also contain residual amounts of host cell proteins (≤0.15 mcg) and/or host cell DNA (≤3 ng). Janssen COVID-19 Vaccine does not contain a preservative, and the vial stoppers are latex-free.
  • Cases of severe COVID-19: 2 instances of COVID-19 requiring hospitalization were reported in the Janssen COVID-19 Vaccine group compared with 29 cases reported in the placebo group. As of 1/22/2021, there were no COVID-19 related deaths in the vaccine group and five in the placebo group.
  • Research relating to pregnancy: In a reproductive developmental toxicity study, female rabbits were administered 1 mL of the Janssen COVID-19 Vaccine (a single human dose is 0.5 mL) by intramuscular injection seven days prior to mating and on Gestation Days 6 and 20 (i.e., one vaccination during early and late gestation, respectively). No vaccine-related adverse effects on female fertility, embryo-fetal or postnatal development up to Postnatal Day 28 were observed.

More vaccines in development and trials may receive emergency use authorization for approval in the future. This includes the AstraZeneca and Novavax vaccines.

Comparing Vaccine Options

The FDA cautions that clinical trials are conducted under widely varying conditions. Adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in another drug’s clinical trials. Plus, the rates of adverse effects in a clinical trial may not reflect the rates observed in the real world. Given that disclaimer, we can look at the rates of adverse effects from a 10,000-foot view to summarize how these vaccines stack up. You will find manufacturer data and many links to research throughout this article. Please feel free to dig deeper into the evidence and draw your own conclusions. This article only compares the three vaccines that currently have FDA emergency use or full authorization in the United States.

Comparing Efficacy of COVID-19 Vaccines  

In a perfect world, a vaccine would be 100% effective with zero side effects. The WHO and the FDA called for a minimum efficacy of 50% for COVID-19 vaccines. For example, if a vaccine is 50% effective, taking the vaccine would reduce your chances of developing COVID-19 by 50%. In clinical trials, vaccine efficacy is measured by giving some participants the vaccine, some participants a placebo, then measuring how many people get the virus. In the Pfizer clinical trial with 43,661 participants, researchers waited for 170 people to test positive for COVID-19. Then they looked at who out of these 170 had received the vaccine or placebo. Of the 170, 8 (about 5%) had the vaccine, making the vaccine 95% effective in preventing COVID-19 infection.

Effectiveness is how well a vaccine works in the real world. We hope vaccine effectiveness will match the efficacy seen in clinical trials, and time will tell as we see more data. Effectiveness is measured by the CDC using many different methods. It is challenging to compare vaccine efficacy between different clinical trials, and it is not an apples-to-apples comparison. The Moderna and Pfizer vaccines both have a high efficacy rate of 94-95%. Although the Janssen vaccine’s efficacy is 66.1%, trials showed only 2 cases of COVID-19 requiring hospitalization in the vaccine group compared with 29 cases reported in the placebo group. There were no COVID-19 related deaths in the vaccine group and five in the placebo group. It is a huge win if vaccines can help prevent severe COVID-19 infections, hospitalizations, and deaths.

Since the original clinical trials, there has been additional research on the effectiveness of the mRNA vaccines during pregnancy. Research on the Pfizer vaccine shows rates of efficacy during pregnancy are in line with efficacy seen in the non-pregnant population.

Comparing Adverse Effects

There is always the possibility of a severe allergic reaction with any vaccine. This is rare, but it does happen. Looking at rates of adverse effects, they are highest with the Moderna vaccine, slightly lower with Pfizer, and lowest with Janssen. The Janssen trial included much fewer participants than the other two vaccines. The takeaway is that having adverse effects like fever, muscle soreness, nausea, pain, or swelling at the injection site is common with all vaccines.

It is possible that your immune system causes inflammation in your heart in response to one of the mRNA vaccines. Myocarditis is inflammation of the heart muscle. Pericarditis is inflammation of the heart’s outer lining. Symptoms include chest pain, shortness of breath, and feeling like your heart is beating very fast. According to the CDC, “The known risks of COVID-19 illness and its related, possibly severe complications, such as long-term health problems, hospitalization, and even death, far outweigh the potential risks of having a rare adverse reaction to vaccination, including the possible risk of myocarditis or pericarditis.” There is also evidence that the risk of myocarditis or pericarditis is increased with a COVID-19 infection.

If you have had dermatological fillers, you may consider talking to your doctor or midwife before getting the Moderna vaccine. There were three cases where vaccine recipients had fillers and experienced facial swelling likely related to vaccination. The American Society for Dermatologic Surgery published guidance stating evidence suggests these reactions can be immunologically triggered by viral and bacterial illness, vaccinations such as the influenza vaccine, and dental procedures. These rare adverse events and patients already treated with dermal fillers should not be discouraged or precluded from receiving vaccines of any kind.

Both the mRNA vaccines (Moderna and Pfizer) had a few cases of Bell’s Palsy, but the information currently available is insufficient to determine a causal relationship with the vaccine. We will have to wait to find out if this was due to the vaccines, and for more information on the more recent research, see this article.

The Pfizer and Janssen trials reported significant events to disclose, but there is not enough information to determine a causal relationship to the vaccine. The Pfizer vaccine trial had 7 cases of appendicitis in the vaccine group and 4 in the placebo group. Janssen had more cases of blood clots in the vaccine group and four seizures in the vaccine group vs. 1 in the placebo group. Plus, six cases of tinnitus (ringing in your ears) in the vaccine group. We will hopefully see more data to establish if these outcomes result from the vaccines. If these are due to the vaccines, we should have better numbers of the risk of experiencing these outcomes in the future.

While one vaccine is not recommended over another, the CDC states, “all women aged <50 years should be aware of the rare risk of TTS (Thrombosis with thrombocytopenia syndrome, involving blood clots) after receipt of the Janssen COVID-19 vaccine and the availability of other currently FDA-approved or FDA-authorized COVID-19 vaccines (i.e., mRNA vaccines) for which this risk has not been seen.”

The Research on the Safety of COVID-19 Vaccines During Pregnancy 

Because these vaccines are relatively new, we have limited data on their safety during pregnancy. The initial clinical trials done to get the vaccines approved for use did not include pregnant participants. This is common in a lot of research. Some participants in the trials became pregnant after receiving the vaccine, and the CDC monitors these participants and tracking data.

A study of 84 pregnant women who got the Moderna or Pfizer vaccine. 11 were in the first trimester, 39 in the second trimester, and 34 in the third trimester. There was one preterm birth from a woman who went into labor at 35 weeks. The baby born preterm, and one additional baby was admitted to NICU. Otherwise, there were no adverse outcomes reported. The rate of babies born before 37 weeks in the U.S. is 10%, and one study found the NICU admission rate for low-risk women to be between 6-9%. When we compare the rates, we would expect to see in the population compared to the outcomes in this study. It doesn’t look like the vaccine had a negative effect on the participants in this study, for the data reported.

Overall, all of the data available shows the COVID-19 vaccines are well-tolerated among pregnant women. This research shows the rates of mild side effects like pain at the injection site are in line with what the non-pregnant population sees, and in some cases, side effects are less common during pregnancy. One study that included breastfeeding women noted that 5% reported decreased milk supply for 24 hours or less after the first dose, which increased to 7.2% with the second dose.

All three vaccines completed studies in animals before moving to human trials. Toxicity studies by Moderna, Pfizer, and Janssen gave animals vaccines before becoming pregnant and during pregnancy. There were no vaccine-related adverse effects on female fertility, fetal development, or postnatal development. These studies were on rabbits and rats, not humans, but it is promising that researchers found no adverse effects.


Researchers compiled data from multiple surveillance systems to gather information about the safety of vaccines during pregnancy. This included a total of 35,691 participants. When comparing rates of some adverse outcomes, like miscarriage, it was within the range we would expect to see in an average population. You may have seen headlines or posts on social media that the vaccine was associated with a miscarriage rate of 82%. That number is not accurate and was initially pulled from this data. The false rate of 82% was not taking into account pregnancies that were still ongoing. Since then, the researchers updated the study tables to clarify the statistics from this data. Please be aware that the most widely accepted statistic is that 10-15% of clinically recognized pregnancies result in a loss. This number is likely much higher if you include pregnancies that miscarry before being clinically recognized. Miscarriage is extremely common in an average population. We would expect to see a miscarriage rate somewhere in the range of 10-15% in any study of the COVID-19 vaccines during pregnancy, in all stages, and especially including participants in the first trimester when miscarriages are more common.

Another study specifically examined miscarriage rates and found that being vaccinated within 28 days before a miscarriage did not increase your risk for miscarriage.


According to ACOG, claims linking COVID-19 vaccines to infertility are unfounded and have no scientific evidence supporting them. ACOG recommends vaccination for all eligible people who may consider future pregnancy. The mRNA vaccines never enter the nucleus of a cell and cannot cause genetic changes to your DNA. If you are trying to conceive or think you may want children in the future, there is currently no evidence the vaccines would negatively affect infertility.

More Data is Coming

Even though we have limited data now, there is more in the pipeline. Pfizer is conducting a trial to study the vaccine in pregnant women. They initially hoped to enroll 4,000 healthy pregnant women to receive the vaccine between 24-34 weeks. The actual enrollment is 700 participants. The estimated completion date was October 15, 2021, and no results are available. Harvard is starting a study soon that expects to include 10,000 pregnant women who receive the vaccine, although the completion date is not until 2025.

Contribute to Future Research

If you are pregnant and receive a vaccine for COVID-19, you have an opportunity to participate in research that will help future expecting mothers. The CDC has a smartphone-based tool (v-safe) that uses text messages and web surveys to collect data after vaccinations. You are eligible to participate if you receive a vaccine within 30 days before conceiving or during pregnancy. The v-safe pregnancy registry is tracking this information and will help us have more data on the safety and efficacy of COVID-19 vaccines during pregnancy in the future. Please consider registering; your participation is voluntary, and you can opt out at any time.

Additional Considerations for COVID-19 Vaccines

As you are weighing the risks and benefits of the COVID-19 vaccine during pregnancy, there are a few additional points you may want to consider.

Regardless of whether you get the COVID-19 vaccine, you should be limiting your risk of exposure and supporting your immune system. There are also many things you can do to boost your immune system safely during pregnancy. Taking care of your health is even more critical when you are pregnant during a global pandemic.

Some hospitals and birth centers may restrict whether you can have your partner or a support person present if you test positive for COVID-19. If you plan for a birth center, you may have to transfer to a hospital if you test positive. This is another reason you should be cautious about limiting your exposure to COVID-19.

Many states, companies, and businesses are requiring vaccines. In some areas, you need to show proof of vaccination to eat in a restaurant. The company you work for may require proof of vaccine to return to working on-site. Vaccine mandates are very effective in increasing vaccination rates. For some people, this is an effective strategy that benefits the overall health of the population. Others feel this is infringing on their freedom of personal choice. No matter how you feel about vaccine mandates, these may impact you, which may influence your decision to get vaccinated.

When to Get the COVID-19 Vaccine During Pregnancy

There are no specific guidelines as to an ideal timeframe during pregnancy to get the COVID-19 vaccine. Some expecting mothers and care providers may choose to avoid vaccines during the first trimester because this period is critical to development. If you want to get the COVID-19 vaccine, please talk to your doctor or midwife about the timing and whether you should space it out with other vaccines.

When COVID-19 vaccines were first available, it was recommended not to get them within 14 days of another vaccine. That stance has changed, and ACOG states that COVID-19 vaccines may be administered simultaneously with other vaccines, including within 14 days of receiving another vaccine, including influenza and Tdap. The CDC acknowledges “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.” Reactogenicity refers to adverse reactions like a fever or soreness at the injection site. Adjuvanted vaccines are those with an added ingredient to trigger an immune response. This means they do not know if you will have more adverse effects from the COVID-19 vaccine if you combine it with other vaccines that give you a stronger immune response. The Tdap vaccine uses aluminum as an adjuvant. There is only one adjuvanted flu vaccine for those 65 and older.

What to Expect If You Get the Vaccine

Before your appointment, talk to your doctor or midwife about what to do if you get a fever. Fever is a common side effect of all of the available COVID-19 vaccines. In the clinical trials for the three approved vaccines, it ranged from 9-15%. According to the American College of Obstetricians and Gynecologists, pregnant women who experience fever following vaccination should be counseled to take acetaminophen. Acetaminophen has been proven safe for use in pregnancy and does not appear to impact antibody response to COVID-19 vaccines.

Acetaminophen is an antipyretic, which is a medication that can reduce a fever. There is a past episode of the podcast about fevers in pregnancy and the use of acetaminophen. Some research challenges the use of acetaminophen during pregnancy, and you can learn more in this episode. If you plan to get a COVID-19 vaccine, talk to your doctor or midwife about how to treat fever and whether to take any antipyretic.

At your appointment, you will get a shot in your upper arm with the COVID-19 vaccine. Pain and swelling at the injection site are common. You will likely be asked to stick around for about 15 minutes after the shot to monitor for immediate adverse or allergic reactions.

If you experience any side effects and have any questions or concerns in the days following the vaccine, please contact your doctor or midwife. Mild side effects are common and if you feel fatigued or under the weather, give yourself time to rest and recuperate. Please consider participating in the CDCs v-safe registry to share information that can benefit pregnant mothers by having more data in the future.  

Final Thoughts

Whether or not to get vaccinated may be a no-brainer choice for you. Many expecting parents are struggling with whether or not to get the COVID-19 vaccine. There will always be unknowns. From the research I have examined, there is no indication that scientists are missing a dangerous risk or a long-term outcome we have yet to see from the vaccine. The same is true for a COVID-19 infection.

At the start of this article, I ran through a list of questions I ask when evaluating a vaccine. You may consider some of these questions for yourself. Hopefully, this article has given you some answers.

  • 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?
  • What is your current health status? Do you have any underlying conditions that predispose you to a more severe case of COVID-19?
  • What is your likelihood of exposure? Are you often around many other people in an indoor setting without masks? Does your job require you to be face to face with people daily? Do you have a spouse or other children who may increase your exposure due to their social interactions?
  • What is the vaccination rate or case rate where you live?
  • Are you in a position where vaccine mandates will significantly impact your life if you choose not to be vaccinated? Is that important to you?

There is no one size fits all answer to these questions. All you can do is make the best decision for you and your baby with the information you have right now.

Talk to Your Doctor or Midwife 

Please talk to your doctor or midwife about the COVID-19 vaccine. If you have questions or concerns, bring them up. Your doctor or midwife is your trusted partner during your pregnancy. They bring a lot of knowledge and experience to help guide you through these decisions.

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

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