Your provider offers you a flu shot, and you are not sure what to do. You have heard it protects your baby. You have also heard it barely worked last year and that the guidance keeps changing. Both have some truth to them, and you have choices beyond just opting in or opting out. In this episode, you will learn what the research shows about the flu shot during pregnancy, how safe it is, how well it works, when to get it, and which shot to ask for.

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Why the Flu Is Riskier During Pregnancy

Influenza, or the flu, is a contagious respiratory illness. It spreads through droplets when someone coughs or sneezes. You can also pick it up from a surface and then touch your face. Symptoms include fever, cough, sore throat, muscle aches, headache, and fatigue. Unlike a cold, which builds gradually, the flu usually hits suddenly and hard. Symptoms typically last about a week, although a cough can linger.

In most healthy adults, the flu runs its course without complications. Pregnancy changes that picture. Your heart pumps more blood, and your lungs work harder. Your immune system also shifts to protect both you and your baby. In fact, a Stanford University study found that pregnant women have an unusually strong immune response to the flu. This may help explain why pregnant women tend to get sicker. As a result, complications like pneumonia and hospital stays are more likely.

The 2009 flu pandemic showed how serious this can be. In its first months, pregnant women accounted for 5 percent of all reported deaths from the pandemic virus. The researchers behind this CDC analysis concluded that pregnant women faced a disproportionately high risk of dying. Thankfully, most flu seasons are far milder than a pandemic. Still, pregnancy adds risk every season.

The flu can also affect your baby through fever, one of its main symptoms. A review of 46 studies linked fever during pregnancy to a higher risk of certain birth defects. For this reason, both preventing the flu and treating a fever matter.

The Flu in Babies and Young Children

Babies cannot get a flu shot until they are six months old. That leaves them without their own protection when the flu is most dangerous. According to the CDC, the flu sends between 6,000 and 25,000 children younger than five to the hospital each year. Flu deaths in children during regular seasons have ranged from 37 to 297 per year. The 2024-25 season reached the top of that range. It is easy to assume these are children with other health problems. However, that is often not the case. In the 2024-25 season, about 6 in 10 children younger than five hospitalized with the flu had no underlying medical condition.

These statistics may sound scary. This helps explain why the flu vaccine is advocated for the medical community.

How the Flu Shot Protects Your Baby

A vaccine shows your immune system an inactivated virus or a piece of one. Your body learns to recognize it and makes antibodies, which takes about two weeks. During pregnancy, those antibodies cross the placenta and give your baby temporary protection. This is called passive immunity. It fades over the first few months, but it covers your baby until they can get their own shot. This is the main principle underlying why some vaccines are recommended during pregnancy.

Randomized controlled trials, the strongest type of study, have tested this benefit. In one trial, more than 2,100 pregnant women received either a flu shot or a placebo. The flu shot cut confirmed flu by about half in the mothers. It also cut flu by about half in their babies during the first six months. Other studies show a similar pattern. For example, a 2024 study looked at babies younger than six months. When their mothers got a flu shot during pregnancy, they were 39% less likely to be hospitalized with the flu. Protection was strongest in babies younger than three months, at 53%.

After birth, you continue to pass antibodies through breast milk. This adds protection. However, according to the American College of Obstetricians and Gynecologists, it does not match the antibodies your baby gets through the placenta. The people around your baby matter too. That is why some parents ask family members to get vaccinated before visiting a newborn.

Why the Flu Shot Changes Every Year

The flu virus changes constantly. Small changes add up from season to season, a process called antigenic drift. Occasionally, flu viruses from different animals swap genetic material and create an entirely new strain. That is how pandemics like the one in 2009 begin. Because the virus keeps changing, one shot cannot protect you for life. Each year, the World Health Organization recommends which strains to include in the vaccine. It has done this since 1973, using surveillance data from around the world. In the United States, the Food and Drug Administration then selects the final strains. After that, manufacturers need about six months to produce the vaccine.

Since the strains are picked months ahead, every flu shot is a prediction. When the prediction matches the viruses that circulate, the vaccine works better. When the virus drifts after the selection, it works less well.

Flu season peaks in winter, so the Northern and Southern Hemispheres each get their own vaccine. Cold, dry air helps the virus survive, and people spend more time indoors. There is also a theory that lower vitamin D levels in winter play a role.

The Controversy Surrounding Vaccines

Vaccines are one of the most polarizing topics in pregnancy and parenting. Some professionals dedicate their careers to studying vaccine safety. Meanwhile, people on every side feel very strongly about them. As a result, information that appears neutral may still push a pro-vaccine or anti-vaccine agenda.

Most of what you will find from medical organizations and online is strongly in favor of vaccination. At the same time, many parents have real questions about safety, long-term effects, and who funds the research. Those questions deserve honest answers rather than dismissal. My goal is to give you the research as it is, including its limitations. Then you can weigh the evidence and decide what is right for you.

The Role of the CDC and WHO

In recent years, trust in public health agencies has dropped. Some people also worry about the influence of drug companies on the Centers for Disease Control and Prevention and the World Health Organization. However, both run some of the largest disease tracking systems in the world. Much of the flu data in this episode comes from them. The landscape has also shifted. The United States has withdrawn from the World Health Organization. Even so, CDC scientists took part remotely in the February 2026 meeting that chose this season’s strains.

In the United States, the Advisory Committee on Immunization Practices traditionally advises the CDC on vaccines. In 2025, Robert F. Kennedy Jr., the Secretary of Health and Human Services, replaced the committee’s members. The new committee then changed several recommendations. In March 2026, a federal court paused the new appointments and the votes the committee had taken. That ruling is under appeal. We can likely expect more changes to come.

Federal guidance has long shaped the advice of the American College of Obstetricians and Gynecologists, or ACOG. In turn, ACOG shapes what your doctor or midwife recommends. Earlier in 2026, however, ACOG stepped away from the federal committee. In June, it released its own maternal immunization schedule, which 13 medical organizations endorsed. The point here is that there is some disagreement between what these health agencies or medical organizations are recommending.

Flu Shot Guidance for 2026-27

For the flu shot, federal guidance and ACOG agree. Because of the legal uncertainty, the CDC did not issue new recommendations from its advisory committee this year. Instead, it updated its interim clinical considerations in September 2026. Those keep the existing recommendation in place: an inactivated or recombinant flu shot in any trimester. ACOG recommends the same, along with several other major medical groups.

All three strains in this season’s vaccine are new compared to last year. One is an H3N2 strain chosen to better match subclade K, the virus behind last season’s surge. Every flu shot this season is trivalent. In other words, it targets three strains: two influenza A strains and one influenza B strain.

How Well the Flu Shot Works

No flu shot prevents every case. To measure how well it works, researchers compare vaccinated and unvaccinated people who end up at the doctor or in the hospital with the flu. These are observational studies, so they have limitations. Still, they give us some data on how the shot performs in the real world. According to the CDC, one study found that a flu shot lowered a pregnant woman’s risk of flu hospitalization by an average of 40%. This study tracked hospitalizations over six years. The researchers adjusted for factors like the flu season and other health conditions.

How well the shot works also changes from year to year. When the vaccine matches the circulating viruses, the CDC reports that it lowers the risk of a doctor visit for the flu by 40-60%. Since 2003, effectiveness has ranged from about 10-60%, depending on the season. Recent seasons show the swings: 36% in 2021-22, then 30%, 44%, and 56% in the next three seasons.

Last season shows what happens with a mismatch. After the strains were picked, the H3N2 virus drifted into a new version called subclade K. That version caused most H3N2 infections last season. As a result, early estimates put overall effectiveness at about 36%.

Is the Flu Shot Safe During Pregnancy?

Doctors have given flu shots to pregnant women for decades, and a large body of research looks at their safety. A systematic review of 40 studies looked at preterm birth, low birth weight, babies born small, birth defects, and pregnancy loss. It did not find increased risks. In fact, it found some evidence that the flu shot may protect against preterm birth and low birth weight.

That research has limitations. Most of these studies are observational, which means researchers track outcomes instead of randomly assigning who gets the vaccine. Critics point to something called the healthy vaccinee bias. People who choose to get vaccinated tend to be healthier to begin with. As a result, vaccines can look safer and more effective than they really are. The randomized trials help address this. However, they mainly measured protection, and they are too small on their own to rule out rare problems.

The flu shot also triggers inflammation, which is part of how any vaccine works. One study measured this inflammatory response in pregnant women. Inflammation also plays a role in preeclampsia and preterm birth, so this is a fair question. The researchers found the vaccine response was much milder and shorter than the response to the flu itself. Still, they said more research should confirm that this mild response is harmless in pregnancy.

Long-Term Effects on Your Baby

Animal research adds another layer. Studies in mice show that activating a mother’s immune system can affect brain development in her offspring. Most of this research uses substances that mimic a serious infection, not a vaccine. A 2026 mouse study compared the two directly. The flu vaccine caused only mild, temporary behavior changes in the offspring. By contrast, the substance that mimics infection had much stronger effects on the developing brain.

In humans, a Canadian study followed more than 104,000 children up to age five. Their mothers had the 2009 pandemic flu vaccine or no vaccine during pregnancy. The study found no link with most health outcomes. It did find a small increase in asthma, which the researchers said other factors may explain.

Flu Shot Side Effects

There are side effects and most are mild and last a day or two. The most common include:

• Soreness, redness, or swelling where you got the shot
• Headache
• Fever
• Muscle aches
• Nausea
• Fatigue

Fainting can happen with any shot, and serious allergic reactions are rare.

The Flu Shot and Autism

Autism is one of the most common concerns parents raise about vaccines. In November 2025, the CDC changed its website on this topic. It now says that “vaccines do not cause autism” is not an evidence-based claim. Major medical groups, including the American Academy of Pediatrics, strongly disagreed.

The first large study on this question was published in 2017. It followed nearly 197,000 children in California. Overall, it found no link between a flu shot during pregnancy and autism. However, it found a small increase in risk when mothers got the shot in the first trimester. The researchers noted this result could be due to chance, because they tested many time periods. They also called for more research.

Several large studies followed. A 2022 study of nearly 85,000 mothers and children in Southern California found no link. About a third of the vaccinated mothers in that study got their shot in the first trimester. A 2020 Swedish study of the 2009 pandemic flu vaccine also found no link, including for first-trimester vaccination. Most recently, a 2025 study from Israel followed more than 153,000 children. At first glance, autism was slightly more common in children of vaccinated mothers, at 3.6% compared to 2.9%. However, that gap disappeared once the researchers accounted for other differences between the two groups of mothers.

All of these are observational studies, so none can prove the flu vaccine has zero effect. On the other hand, the flu is not risk-free for a developing baby either. A large Norwegian study linked fever during pregnancy to a small increase in autism risk. Fever is a main symptom of the flu.

Taken together, the human research has not found a link between the flu vaccine during pregnancy and autism. If timing is a concern for you, waiting until after the first trimester is one option. That is where the one early signal appeared, and the first trimester is the most sensitive period for development.

The 2017 Miscarriage Study

In 2017, a study made headlines for linking the flu shot to miscarriage. It looked at women who got a flu shot in the 28 days before a first-trimester miscarriage. The link only appeared in women who had also been vaccinated the season before. The study covered the 2010-11 and 2011-12 flu seasons. Notably, the researchers stated that their results did not show the vaccine caused miscarriage. They called for more research.

ACOG responded at the time: “In evaluating all of the available scientific information, there is insufficient information to support changing the current recommendation, which is to offer and encourage routine flu vaccinations during pregnancy regardless of the trimester of pregnancy.”

That further research did happen. In 2019, the same research group published a follow-up study covering the next three flu seasons and more than 1,200 miscarriages. It found no link between the flu vaccine and miscarriage. That included women who had been vaccinated the season before.

As with any intervention during pregnancy, the decision is yours, and it should be based on informed consent.

When to Get the Flu Shot

You can get the flu shot in any trimester. Because protection takes about two weeks to build, the CDC says the ideal time is September or October. If you miss that window, a later shot can still help, since the flu often circulates into the spring.

Your stage of pregnancy can also shape the timing. According to the CDC’s interim guidance, a shot in July or August is reasonable if you are in your third trimester then. That earlier timing has been linked to better protection for your baby after birth. On the other hand, the CDC suggests waiting until September or October if you are in your first or second trimester.

The research on timing and your baby’s protection is mixed. One study found that a shot in the second or third trimester gave babies protective antibodies. The key was getting it at least 15 days before birth. The 2024 study in the United States found protection was strongest with a third-trimester shot, at 52%. By comparison, protection was 17% with a first or second trimester vaccine. However, a larger study from Ontario found similar protection in every trimester, at about 64% overall.

Fewer studies focus on the first trimester, since it is such a critical period of development. For this reason, some expecting parents and care providers prefer to wait until after it. Remember, you have options beyond opting in or opting out, and the timing is one of these.

Getting Other Vaccines at the Same Visit

You may also be offered other vaccines around the same time. The Tdap vaccine is recommended between weeks 27 and 36 of pregnancy. The RSV vaccine is given between weeks 32 and 36 during the fall and winter. According to ACOG, you can safely get these at the same visit as your flu shot.

There is one nuance. The Adacel Tdap vaccine package insert describes a clinical trial that gave Tdap and a flu shot together. In that trial, the antibody response to pertactin was lower than with Tdap alone. Pertactin is one part of the vaccine that helps you build immunity to whooping cough. Despite this, ACOG and the CDC consider it safe to give them together. If you would rather space them out, that is an option to discuss with your doctor or midwife. It makes sense to know there’s a lot of pressure in the medical community to get people vaccinated, and the easiest way to satisfy that is to administer vaccines as early as possible.

Choosing Your Flu Shot

Several flu vaccines can be given during pregnancy, including Afluria, Fluarix, FluLaval, Fluzone, Flucelvax, and Flublok. ACOG does not prefer one brand over another. Its statement is that pregnant individuals should receive any licensed, recommended, age-appropriate, inactivated, or recombinant flu vaccine during any trimester.

A few vaccines are not options during pregnancy. The nasal spray vaccine contains a live, weakened virus, so it is not recommended until after your baby is born. The high-dose and adjuvanted shots are for adults 65 and older. In addition, the first mRNA flu vaccine, mFlusiva, was recently approved only for adults 50 and older.

Most flu vaccines grow in fertilized chicken eggs and contain trace amounts of egg protein. Flucelvax, approved in 2012, grows in cells from dog kidneys and is egg-free. Flublok, approved in 2013, uses insect cells and is also egg-free. It contains three times as much hemagglutinin as most other flu shots. That is the virus protein your immune system learns to recognize. If you have an egg allergy, the CDC now says any flu vaccine is fine, with no extra precautions.

Some flu shots contain trace amounts of formaldehyde from processing, far less than what is naturally in your blood. Some also contain gelatin as a stabilizer. If you are vegan, no flu shot is completely free of animal-derived ingredients.

Thimerosal in Flu Shots

Thimerosal is a preservative that contains mercury. Manufacturers only use it in multidose vials, which hold several doses. Single-dose prefilled syringes do not contain it. In June 2025, the Advisory Committee on Immunization Practices voted for thimerosal-free, single-dose flu shots for pregnant women and all adults. However, the court paused that vote too. This season, about 99% of the supply is thimerosal-free, yet at least one multidose vial is back on the market. If you want to avoid thimerosal, ask for a single-dose prefilled syringe.

Medical offices and pharmacies order their vaccines months before flu season. So your options may depend on what your doctor or midwife carries. It’s not like your doctor will give you a menu of options to choose from. They typically stock one type. If you prefer a specific type or brand, call ahead or check with local pharmacies.

If You Get the Flu While Pregnant

Because the flu can be more serious during pregnancy call your doctor or midwife as soon as you have flu symptoms. Prescription antiviral medicine works best when you start it early. In the 2009 pandemic, some pregnant women started treatment more than four days after their symptoms began. They were six times more likely to need intensive care than women treated within two days.

According to the CDC, oseltamivir, sold as Tamiflu, is the preferred treatment during pregnancy. If you are very sick, it can still help after the first 48 hours. On the other hand, the CDC does not recommend baloxavir, sold as Xofluza, during pregnancy or breastfeeding. There are no safety data for it.

For a fever, acetaminophen remains the main option during pregnancy. It has its own controversy, which you can learn about in the episode on Tylenol during pregnancy. For rest, fluids, and over-the-counter medicines, see the episode on getting sick during pregnancy.

According to the CDC, some symptoms need emergency care right away:

• Trouble breathing or shortness of breath
• Pain or pressure in your chest or abdomen
• Sudden dizziness or confusion
• Severe or constant vomiting
• Decreased or no movement from your baby
• A high fever that does not respond to acetaminophen

The Bottom Line on the Flu Shot During Pregnancy

The flu tends to hit harder during pregnancy, and your baby cannot get a flu shot until six months old. That is why the flu vaccine is recommended during pregnancy to protect you and to protect your baby. A flu shot lowers the risk of hospitalization for both of you. However, it will not prevent every case, and how well it works changes each season. Most of the safety research is reassuring, and some questions remain open.

A lot of things during your prenatal visits don’t feel like a choice. It’s presented as, “This is what’s happening at your appointment today.” It’s important that you understand you always have choices beyond simply opting in or out. You can choose when to get it and which type of shot you receive. If you would like to avoid thimerosal, ask for a single-dose prefilled syringe. As with any intervention, you always have the option to decline. It’s really up to you to weigh the risks and the benefits and decide what you are comfortable with and what choice is the right one for you and your baby. Hopefully, after this episode, you feel more empowered to do that.

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