Flu shots and miscarriage: Let’s clear up misunderstandings

A doctor giving a patient a vaccination.
Getting a flu shot during pregnancy is not only safe but strongly recommended.

With flu season in full swing, September is possibly the worst time to release a confusing study about the safety of flu shots for pregnant woman. But that’s what happened, and now doctors across the country are running defense to protect pregnant women and their babies from the flu.

The study in question was funded by the Centers for Disease Control and Prevention (CDC) and published in Vaccine. The CDC promptly released a statement that the study does not quantify miscarriage risk and does not prove flu shots can cause miscarriage, even Vaccine Editor-in-Chief Gregory Poland, CRED, who is also director of vaccine research at the Mayo Clinic, was quoted in The New York Times saying he does “not at all” believe flu shots caused the miscarriages reported in the study.

Unfortunately, click-baiting media outlets and grassroots anti-vaccination advocates got wind of the study. Inflammatory headlines and misinformation added to the confusion about the study, leaving fearful pregnant women scrambling to decide whether to get vaccinated.

Let’s make one thing clear: UT Southwestern Ob/Gyns and infectious disease experts recommend that all pregnant women get the flu shot. The benefits for moms and babies clearly outweigh the risks, no matter what you might have read online. Let’s examine why we can confidently make this recommendation and what to do if you’re on the fence about getting vaccinated for the flu.

Holes in the ‘flu shots and miscarriage’ study

The most important thing I want women to understand is this: This study does not say that you are at increased risk for miscarriage if you are in the first trimester, have a healthy pregnancy, and get a flu shot.

The study looked at a population of women who were diagnosed with a miscarriage during pregnancy and compared them to women who have live births. They then studied whether and when the women received a flu shot during pregnancy. The study did not specify when the women who got flu shots were vaccinated, but it stated that many received a flu shot within 28 days of the miscarriage and also received a flu shot during the previous year’s flu season. 

The definition of pregnancy in the study is very broad. The reported pregnancies could have been diagnoses from doctors, self-reported by the patients, or determined by a lab test only. There was no requirement that the pregnancies were proved to be viable, or have a chance to be successful, before women were included in the analysis.

The majority of miscarriages in the women in the study occurred in the first trimester, with the greatest number occurring between five and seven weeks. This isn’t surprising because miscarriage is so common in the general population. In fact, 80 percent of spontaneous miscarriages occur in the first trimester. There’s no way to know whether these pregnancies were going to be successful regardless of whether the women received flu shots.

Getting a flu shot is still best for mom and baby

The CDC, the American College of Obstetricians and Gynecologists (ACOG), and the American Academy of Pediatrics continue to recommend the flu shot for pregnant women at any stage of pregnancy, not only for the benefit of the mom but also because it provides the baby with antibodies that can help protect the baby after birth. 

Infants cannot get their own flu vaccine until 6 months of age, so the antibodies you pass to your child are vital. As of September 2, 2017, more than 100 pediatric flu deaths already have been reported for the 2016/2017 flu season. The peak flu season traditionally is September through March, but there’s no way to predict with certainty how early the flu season will start or how long it will last. Early indications from countries in the southern hemisphere where flu season has already started suggest this year will see a lot of influenza activity.

Some women worry that the flu shot will make them sick. This is untrue. Flu shots are made from dead viruses that cannot give you the flu – but you may notice some minor side effects such as soreness at the injection site, low-grade fever, or muscle aches, which are annoying but not worrisome.

The nasal spray flu vaccine is not recommended for pregnant women. The spray is made from a live attenuated virus, which means the virus is weakened but still alive and could potentially infect you with the flu. But this year, the CDC is not recommending the spray vaccine for anyone, including children, because it’s likely to be ineffective against the flu strains that are expected to be strongest this flu season. 

What to do if you’re on the fence about getting vaccinated

Getting the flu shot during any trimester of pregnancy is reasonable and safe, and being vaccinated against the flu in the first trimester will not put your baby at risk. But if you’re nervous about getting the flu shot during the first trimester, don’t refuse to be vaccinated. Just hold off until after you reach 20 weeks of pregnancy. The Vaccine study reported there was no increased risk after 20 weeks of pregnancy. You might not be as fully protected from the flu, which can lead to serious complications including hospitalization and even death in pregnant women, but your baby will still get the antibody benefit.

The key takeaway for women is that scientific research studies have never proven a cause/effect relationship between the flu vaccine and miscarriage. In fact, January 2013 study showed no link between miscarriage rates and maternal flu vaccination using clinical data, and an August 2017 study found no increased risk between maternal flu vaccination and birth defects in babies. Even the study published in Vaccine states that the data retrieved demonstrate an association, not a cause/effect relationship, between flu shots and miscarriage. 

I appreciate that researchers continue to question what is and isn’t safe for pregnant women and their babies. However, as medical professionals, we have to be careful about what we say and how we say it. This inconclusive study is a prime example of how associative data, particularly when it is distributed without proper context, can do more harm than good for public health.

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