Vaccines During Pregnancy: Which Are Safe?

Why Is Vaccination Important During Pregnancy?

Vaccination during pregnancy protects both the mother and baby. Pregnancy naturally changes the immune system, making infections like influenza and whooping cough more dangerous. Maternal antibodies pass through the placenta, giving newborns critical protection during their first months when they are too young to be vaccinated themselves.

During pregnancy, the immune system undergoes significant changes to prevent rejection of the developing fetus. While these adaptations are essential for a healthy pregnancy, they also make pregnant women more vulnerable to certain infections. The body's reduced ability to fight off respiratory viruses, for example, means that influenza during pregnancy carries a higher risk of hospitalization, pneumonia, and even preterm labor compared to the general population.

Vaccination works on two levels during pregnancy. First, it directly protects the mother from potentially serious infections that could harm her health or the pregnancy itself. Research published in The Lancet has consistently shown that pregnant women who contract influenza have significantly higher rates of ICU admission and adverse pregnancy outcomes including preterm birth and low birth weight.

Second, and equally important, vaccination triggers the mother's immune system to produce antibodies that cross the placenta and enter the baby's bloodstream. This process, known as passive immunity, provides the newborn with protection from the moment of birth. This is particularly valuable because most vaccines cannot be given to infants until they are at least 2 months old, leaving a dangerous gap during which the baby is entirely dependent on maternal antibodies for defense.

The concept of maternal immunization is supported by decades of research and is endorsed by every major medical organization worldwide, including the World Health Organization (WHO), the American College of Obstetricians and Gynecologists (ACOG), the Centers for Disease Control and Prevention (CDC), and the Royal College of Obstetricians and Gynaecologists (RCOG). The evidence base includes studies involving hundreds of thousands of pregnant women, consistently showing that recommended vaccines are both safe and effective during pregnancy.

How Antibodies Transfer to the Baby

When you receive a vaccine during pregnancy, your immune system responds by producing specific antibodies against the targeted disease. These antibodies, primarily of the IgG class, are actively transported across the placenta to the fetus during the third trimester. The transfer is most efficient in the final weeks of pregnancy, which is why the timing of certain vaccines (such as Tdap between weeks 27-36) is carefully chosen to maximize the amount of protective antibodies the baby receives before birth.

After delivery, these maternal antibodies continue to circulate in the baby's blood, providing protection for approximately 3 to 6 months. This period bridges the critical gap until the infant's own immune system matures enough to respond to childhood vaccines. Studies have demonstrated that babies born to vaccinated mothers have significantly higher antibody levels and lower rates of infections like pertussis and influenza during their first months of life.

Which Vaccines Are Recommended During Pregnancy?

Four vaccines are currently recommended during pregnancy: the inactivated influenza (flu) vaccine, the Tdap vaccine (tetanus, diphtheria, pertussis), COVID-19 mRNA vaccines, and the RSV vaccine. All of these are inactivated or mRNA-based and do not contain live virus, making them safe for use during pregnancy.

The recommendations for vaccination during pregnancy are based on careful evaluation of both the risks of the diseases and the safety and efficacy of the vaccines. International health authorities regularly review the evidence and update their guidelines. The currently recommended vaccines represent those for which the benefits clearly outweigh any potential risks, supported by robust clinical trial data and extensive post-marketing surveillance.

It is important to understand that not all vaccines are the same. The key distinction is between inactivated vaccines (which contain killed virus or parts of virus and cannot cause infection) and live attenuated vaccines (which contain weakened but active virus). Only inactivated and mRNA-based vaccines are recommended during pregnancy. This safety principle has guided maternal immunization policy for decades and has been validated by extensive real-world data.

Your healthcare provider will review your vaccination history at your first prenatal appointment and recommend a personalized immunization plan based on your specific circumstances, including your trimester, any previous vaccinations, underlying health conditions, and the current epidemiological situation in your region.

Is the Flu Shot Safe During Pregnancy?

Yes, the inactivated influenza vaccine (flu shot) is safe and strongly recommended at any stage of pregnancy. Pregnant women face a significantly higher risk of severe flu complications including pneumonia, hospitalization, and preterm labor. The flu shot protects both mother and baby, with antibodies passing to the newborn and providing protection for approximately 6 months.

Influenza poses a unique threat during pregnancy. The physiological changes that accompany pregnancy, including alterations in heart rate, lung capacity, and immune function, make pregnant women considerably more susceptible to severe influenza complications. Data from multiple influenza seasons shows that pregnant women are 3 to 4 times more likely to be hospitalized with influenza than non-pregnant women of the same age.

The inactivated influenza vaccine has been used in pregnant women for over 60 years, making it one of the most extensively studied vaccines in this population. A landmark systematic review published in The Lancet Infectious Diseases analyzed data from over 100,000 pregnant women and found no increased risk of miscarriage, stillbirth, preterm birth, low birth weight, or congenital abnormalities associated with influenza vaccination. The WHO considers it one of the highest priority vaccines for pregnant women globally.

The flu shot can be given during any trimester of pregnancy. If flu season is approaching or underway, vaccination should not be delayed regardless of gestational age. The vaccine takes approximately 2 weeks to provide full protection. Studies have shown that vaccination during pregnancy reduces the risk of flu-related hospitalization by 40% in the mother and decreases the incidence of influenza in infants under 6 months by approximately 50%.

When to Get the Flu Shot

The influenza vaccine is recommended before or during flu season, regardless of which trimester you are in. In the Northern Hemisphere, flu season typically runs from October through March, while in the Southern Hemisphere it runs from April through September. If you become pregnant during flu season, getting vaccinated as early as possible provides the best protection. The vaccine remains effective throughout the season and does not need to be repeated during the same pregnancy.

Flu Risks for the Unborn Baby

Influenza infection during pregnancy does not only affect the mother. High fever, particularly in the first trimester, has been associated with a small increased risk of neural tube defects. More significantly, severe maternal influenza can trigger preterm labor, and babies born to mothers who were hospitalized with influenza show higher rates of low birth weight. By preventing flu through vaccination, these risks to the baby are substantially reduced.

When Should You Get the Tdap Vaccine in Pregnancy?

The Tdap vaccine (tetanus, diphtheria, pertussis) should be given between weeks 27 and 36 of every pregnancy, ideally around weeks 27 to 32. This timing maximizes antibody transfer to the baby, providing over 90% protection against whooping cough (pertussis) during the first 2 months of life when the disease is most dangerous.

Whooping cough, caused by the bacterium Bordetella pertussis, is one of the most dangerous infectious diseases for very young infants. Babies under 2 months old are too young to receive their own pertussis vaccination, yet this is precisely the age when the disease is most severe and potentially fatal. Infants with whooping cough can develop violent coughing fits that make it impossible to breathe, leading to hospitalization, pneumonia, brain damage, and in the worst cases, death.

Maternal Tdap vaccination is the most effective strategy to protect newborns during this vulnerable window. When the vaccine is given during the third trimester, the mother's immune system produces high levels of pertussis-specific antibodies that are actively transported across the placenta. By the time the baby is born, these antibodies provide immediate protection against the disease.

Large-scale studies from the United Kingdom, where maternal Tdap vaccination has been routine since 2012, demonstrate that this approach is approximately 90-93% effective at preventing pertussis in infants under 2 months old. The effectiveness remains strong at around 69% for infants up to 3 months of age, providing crucial coverage until the baby can receive their own first dose of pertussis vaccine.

A critical point that many people are unaware of is that the Tdap vaccine must be given during every pregnancy, even if you received it during a previous pregnancy or as an adult booster. The reason is that antibody levels decline between pregnancies, and each baby needs a fresh supply of maternal antibodies. Research has shown that antibodies transferred from a booster given years earlier are insufficient to protect a newborn.

Optimal Timing: Why Weeks 27-32

The recommended window for Tdap vaccination is between weeks 27 and 36, but earlier within this window is generally better. It takes approximately 2 weeks for the body to mount a full antibody response after vaccination, and the active transport of antibodies across the placenta is most efficient during the final 6 to 8 weeks of pregnancy. By vaccinating around weeks 27-32, you allow enough time for robust antibody production while maximizing the duration of placental transfer before delivery.

If you did not receive the Tdap vaccine during pregnancy, you should receive it as soon as possible after delivery to reduce the risk of transmitting pertussis to your newborn. However, post-delivery vaccination provides significantly less protection for the baby, as there is no placental antibody transfer. This underscores the importance of timely vaccination during pregnancy.

Safety of Tdap During Pregnancy

The Tdap vaccine has been extensively studied in pregnant women, with data from millions of vaccinated pregnancies confirming its safety. A comprehensive safety review by the CDC's Vaccine Safety Datalink, which analyzed over 300,000 Tdap-vaccinated pregnancies, found no increased risk of stillbirth, neonatal death, preterm birth, small-for-gestational-age infants, or major birth defects. The most common side effects are mild and temporary, including soreness at the injection site and occasional fatigue.

Is the COVID-19 Vaccine Safe During Pregnancy?

Yes, COVID-19 mRNA vaccines (Pfizer-BioNTech and Moderna) are recommended during pregnancy at any trimester. Large studies involving over 200,000 pregnant women show no increased risk of miscarriage, birth defects, or pregnancy complications. COVID-19 infection during pregnancy, however, significantly increases the risk of ICU admission, preterm birth, and stillbirth.

The safety of COVID-19 vaccines during pregnancy was initially a major concern for many expectant parents, but extensive real-world evidence has now firmly established their safety profile. The v-safe surveillance system in the United States, which tracked over 200,000 pregnant vaccine recipients, found that the rates of miscarriage, stillbirth, preterm birth, and small-for-gestational-age infants were no higher among vaccinated women than in the general pregnant population.

The risks of COVID-19 infection during pregnancy, by contrast, are well-documented and significant. Pregnant women with COVID-19 are 5 to 6 times more likely to require ICU admission compared to non-pregnant women of the same age. They face increased rates of preeclampsia, preterm birth, cesarean delivery, and stillbirth. The Delta and subsequent variants proved particularly dangerous for unvaccinated pregnant women, with some studies showing a 22-fold increase in maternal mortality among those with severe COVID-19.

COVID-19 mRNA vaccines work by instructing cells to produce the spike protein found on the surface of the SARS-CoV-2 virus. This triggers an immune response without using any live virus. The mRNA does not enter the cell nucleus or interact with DNA, and it is broken down by the body within days of vaccination. There is no mechanism by which the vaccine could affect fetal development, and this has been confirmed by extensive animal and human studies.

Like the flu shot and Tdap, COVID-19 vaccination during pregnancy also generates protective antibodies that transfer across the placenta. Studies published in JAMA Pediatrics have shown that infants born to vaccinated mothers have detectable COVID-19 antibodies at birth, providing early protection against the virus during a period when severe COVID-19 in infants, while rare, can occur.

What Is the RSV Vaccine for Pregnant Women?

The RSV (respiratory syncytial virus) vaccine Abrysvo is a newer vaccine approved for use during weeks 32-36 of pregnancy during RSV season. It protects newborns from severe RSV bronchiolitis, which is the leading cause of hospitalization in infants under 6 months. The vaccine reduces the risk of severe RSV illness in newborns by approximately 57-82%.

Respiratory syncytial virus is an extremely common respiratory pathogen that infects virtually all children by age 2. While older children and adults typically experience mild cold-like symptoms, RSV can cause severe and sometimes life-threatening bronchiolitis and pneumonia in very young infants, particularly those under 6 months of age. RSV is the single most common cause of hospitalization in infants worldwide, accounting for approximately 3.2 million hospital admissions globally each year.

The development of a maternal RSV vaccine represents a major breakthrough in neonatal disease prevention. The Abrysvo vaccine, manufactured by Pfizer, received approval from the FDA in 2023 for use during pregnancy. It works by stimulating the mother's immune system to produce RSV-specific antibodies that transfer to the baby through the placenta, providing protection from birth.

Clinical trials demonstrated that maternal RSV vaccination reduced medically attended severe RSV-associated lower respiratory tract illness in infants by approximately 82% within the first 90 days of life and 69% within the first 180 days. These results are particularly significant given that no RSV vaccine exists for infants under 6 months old.

The RSV vaccine is recommended during weeks 32-36 of pregnancy when RSV season is anticipated. In temperate climates, RSV typically circulates from late autumn through early spring. Your healthcare provider will advise you on the optimal timing based on your due date and local RSV activity. The vaccine is a single dose and can be given alongside other recommended pregnancy vaccines.

RSV Vaccine vs. Monoclonal Antibody

An alternative approach to protecting newborns from RSV is the monoclonal antibody nirsevimab (Beyfortus), which is given directly to the baby shortly after birth. Your healthcare provider may recommend one approach or the other, but not both. The maternal vaccine and infant monoclonal antibody provide similar levels of protection, and the choice often depends on timing, RSV seasonality, and local availability.

What Vaccines Should You Avoid During Pregnancy?

Live vaccines should be avoided during pregnancy because they contain weakened but active viruses that could theoretically pose a risk to the developing fetus. These include MMR (measles, mumps, rubella), varicella (chickenpox), BCG, yellow fever, live attenuated influenza (nasal spray), and oral polio vaccine. If you need these vaccines, get them at least 4 weeks before trying to conceive or after delivery.

The distinction between live and inactivated vaccines is fundamental to understanding vaccine safety during pregnancy. Live attenuated vaccines contain weakened versions of the virus or bacterium that can replicate in the body to stimulate an immune response. While these vaccines are safe and effective for most people, the theoretical concern during pregnancy is that the weakened pathogen could cross the placenta and affect the developing fetus.

It is important to emphasize that this is largely a theoretical risk based on the principle of caution. In practice, extensive surveillance of women who inadvertently received live vaccines during pregnancy (often before they knew they were pregnant) has not identified any pattern of adverse outcomes. For example, the CDC has maintained a registry of women who received MMR vaccine during pregnancy, and no cases of congenital rubella syndrome have been attributed to the vaccine. Nevertheless, the precautionary principle dictates that live vaccines should be avoided when possible.

If your immunity to measles, mumps, rubella, or varicella is inadequate, the ideal approach is to receive these vaccines before becoming pregnant and wait at least 4 weeks before trying to conceive. If you discover during prenatal screening that you lack immunity to rubella or varicella, these vaccines should be given immediately after delivery, even if you are breastfeeding. Live vaccines are safe during breastfeeding because the weakened viruses do not pass into breast milk in significant quantities.

What Are Common Side Effects of Vaccines During Pregnancy?

Side effects from recommended pregnancy vaccines are generally mild and short-lived. The most common reactions include soreness at the injection site, mild fatigue, headache, muscle aches, and occasionally a low-grade fever. These symptoms typically resolve within 1-2 days and are a normal sign that the immune system is responding to the vaccine.

Understanding what to expect after vaccination can help alleviate anxiety. The side effects of vaccines given during pregnancy are essentially the same as those experienced by non-pregnant individuals, and large safety studies have confirmed that there is no increased frequency or severity of reactions in pregnant women. The most common reaction is local soreness at the injection site, which affects roughly 60-80% of people regardless of pregnancy status.

Systemic side effects, meaning those that affect the whole body, are less common but can include fatigue, headache, muscle aches, and low-grade fever. These reactions are more frequently reported with the COVID-19 vaccine than with the flu shot or Tdap, particularly after the second dose or booster. However, even with the COVID-19 vaccine, most pregnant women report only mild to moderate symptoms that resolve within 24-48 hours.

Fever during pregnancy warrants attention because sustained high temperatures have been associated with a small increased risk of neural tube defects during the first trimester. If you develop a fever above 38 degrees Celsius (100.4 degrees Fahrenheit) after vaccination, taking acetaminophen (paracetamol) is safe during pregnancy and can help reduce the temperature. Ibuprofen should generally be avoided during pregnancy, particularly in the third trimester.

Serious allergic reactions (anaphylaxis) to vaccines are extremely rare, occurring in approximately 1-2 per million doses. For this reason, healthcare providers typically ask you to wait 15-30 minutes after vaccination for monitoring. If you have a known allergy to any vaccine component, discuss this with your healthcare provider before vaccination.

When to Contact Your Healthcare Provider

While most side effects are self-limiting, you should contact your healthcare provider if you experience fever above 38.5 degrees Celsius (101.3 degrees Fahrenheit) that does not respond to acetaminophen, symptoms that worsen after 48 hours rather than improving, signs of an allergic reaction such as difficulty breathing, swelling of the face or throat, or widespread rash, or any unusual or concerning symptoms following vaccination.

What About Travel Vaccines During Pregnancy?

Some travel vaccines are safe during pregnancy while others should be avoided. Hepatitis A and hepatitis B vaccines (both inactivated) can be given if needed. Yellow fever, typhoid (oral), Japanese encephalitis, and other live vaccines should generally be avoided. Always consult a travel medicine specialist at least 6-8 weeks before planned travel during pregnancy.

International travel during pregnancy introduces unique vaccination considerations. The decision to administer travel-related vaccines must weigh the risk of exposure to the disease at the destination against the theoretical or known risks of the vaccine during pregnancy. In some cases, the safest option may be to postpone travel to high-risk areas until after delivery.

Several inactivated travel vaccines can be given during pregnancy when the risk of exposure justifies vaccination. Hepatitis A and hepatitis B vaccines are both inactivated and considered safe. Inactivated polio vaccine can be given if needed for travel to polio-endemic regions. The meningococcal vaccine is also inactivated and can be used if indicated.

Yellow fever vaccine presents a particular dilemma because it is a live vaccine, yet yellow fever itself carries a high mortality rate. In most situations, travel to yellow fever-endemic areas should be postponed during pregnancy. However, if travel is unavoidable and the risk of exposure is high, the yellow fever vaccine may be considered after careful discussion with a healthcare provider, as the documented risks of the vaccine appear to be low.

Malaria prevention during pregnancy is primarily achieved through medications (chemoprophylaxis) and mosquito bite prevention measures rather than vaccination. If you are planning travel to a malaria-endemic region during pregnancy, consult a travel medicine specialist for appropriate antimalarial medications, as some are safe during pregnancy while others are not.

Planning Pre-Conception Vaccinations

If you are planning to become pregnant and anticipate needing travel vaccines, the ideal approach is to complete all necessary vaccinations before conception. Live vaccines should be given at least 4 weeks before attempting to conceive. Inactivated vaccines can be given at any time before or during pregnancy without concern. Keeping your routine vaccinations up to date before pregnancy simplifies your care and reduces the number of vaccines needed during pregnancy.

Can You Get Vaccinated While Breastfeeding?

Yes, virtually all vaccines including live vaccines are safe during breastfeeding. Neither inactivated nor live vaccines pose a risk to the breastfed infant. If you missed any vaccines during pregnancy or need live vaccines (MMR, varicella), the postpartum period is an excellent time to get them. Vaccine antibodies may also pass through breast milk, providing additional protection.

Breastfeeding is not a contraindication for any routinely recommended vaccine. This includes live vaccines that are avoided during pregnancy. The reasoning is straightforward: while live vaccine viruses could theoretically cross the placenta and reach the fetus, they do not pass into breast milk in quantities sufficient to cause infection in the nursing infant. The only exception historically noted is the smallpox vaccine, which is no longer routinely used.

The postpartum period offers an important opportunity to catch up on any vaccines that were missed or deferred during pregnancy. Women who lack immunity to rubella or varicella should receive MMR and varicella vaccines as soon as possible after delivery. The Tdap vaccine should be given to any postpartum woman who did not receive it during pregnancy, ideally before leaving the hospital, to reduce the risk of transmitting pertussis to the newborn.

Emerging research suggests that vaccine antibodies can pass into breast milk, potentially providing some additional protection to the breastfed infant. While the extent of this protection is still being studied, it provides another reason to stay up to date with vaccinations while breastfeeding. COVID-19 antibodies, in particular, have been detected in breast milk following maternal vaccination, though the clinical significance of this finding is still under investigation.

How Should You Plan Your Pregnancy Vaccination Schedule?

The optimal vaccination schedule during pregnancy includes the flu shot at any point during flu season, the Tdap vaccine between weeks 27-36 (ideally 27-32), COVID-19 vaccine if not up to date, and the RSV vaccine between weeks 32-36 during RSV season. Multiple vaccines can safely be given at the same visit.

Creating a vaccination plan during pregnancy involves coordinating several vaccines across different trimesters. The good news is that these vaccines can be administered at the same appointment without reducing their effectiveness or increasing side effects. Receiving multiple vaccines simultaneously is standard practice in prenatal care and is supported by extensive safety data.

During your first prenatal visit, your healthcare provider should review your vaccination history and check your immunity to common diseases including rubella and varicella through blood tests. This early assessment allows time to plan which vaccines you will need during pregnancy and identify any live vaccines that may need to be given after delivery.

Partners and Family Members

Protecting a newborn from infectious diseases extends beyond maternal vaccination. A strategy known as "cocooning" involves ensuring that all close contacts of the baby, including the partner, grandparents, siblings, and caregivers, are up to date with their vaccinations. This is particularly important for pertussis (whooping cough) and influenza, as newborns most often contract these diseases from household contacts.

Encourage your partner and anyone who will have close contact with the baby to receive the Tdap vaccine at least 2 weeks before meeting the newborn. Annual flu vaccination is also recommended for all household members. For COVID-19, ensuring that close contacts are up to date with recommended boosters provides an additional layer of protection.

Frequently Asked Questions