Yes, Pregnant Women Should Still Get a Flu Shot

Korin Miller
Updated
What you need to know about that new study.

A new study found an association between getting the flu shot when pregnant and having a miscarriage. Understandably, people are freaking out. "Study Prompts Call to Probe Link Between Flu Shot and Miscarriage", one headline read. "Study Confirms Link Between Flu Vax and Miscarriage", another said.

But the findings here are far from conclusive—even the study’s authors are still urging pregnant women to get their flu shots.

So let's be clear right off the bat: You should still get the flu shot when you're pregnant.

The Centers for Disease Control and Prevention (CDC) and the American Congress of Obstetricians and Gynecologists (ACOG) still recommend that women get a flu shot during their pregnancy—at any stage—because the flu can be so dangerous to pregnant women.

In light of this study, the CDC even released a guidance for health care providers that reiterated its recommendation that "pregnant women get a flu vaccine during any trimester of their pregnancy because flu poses a danger to pregnant women and a flu vaccine can prevent influenza in pregnant women.”

But the study, published online last week in the journal Vaccine, poses a lot of questions.

The study found an association between the flu shot and miscarriage—but only in certain circumstances.

For the study, researchers analyzed medical records for 485 women who miscarried and matched that up with another 485 medical records from women who were pregnant during the same time but delivered full-term babies or had a stillbirth at 20 weeks or more (this was the control group).

The researchers looked at medical records specifically over the course of two flu seasons (from 2010 to 2011 and 2011 to 2012). In this sample, the researchers found an association between the flu shot and miscarriage—but only among women who had gotten the vaccine the previous year (which contained the 2009 H1N1 virus) and also got a flu shot the following year within 28 days of the miscarriage.

If that sounds oddly specific, you're right. The study does not estimate a risk for miscarriage—it just shows us an association in a very specific set of circumstances.

Still, this link between the flu shot and miscarriage was "unexpected," lead study author James Donahue, Ph.D., M.P.H., an epidemiologist with the Marshfield Clinic Research Institute, tells SELF. It was especially surprising because the same group of researchers performed another study before the 2009 H1N1 flu pandemic that found no association between the vaccine and miscarriages. So these results contradict the group's previous ones.

Before you freak out, you should know the study has serious limitations.

First off, the study establishes a correlation—not causation. So, although researchers found an association between the flu vaccine and miscarriage (under these very specific circumstances), they didn’t actually prove that getting the flu shot caused those miscarriages. Another factor entirely may be responsible for the link. For example, it's possible that women who are already at a high risk of miscarrying also go to their ob/gyn's more often, where they got a flu shot. Unfortunately, miscarriages happen—ACOG estimates they occur in about 10 percent of all recognized pregnancies—and it’s possible that women who suffered miscarriages also just happened to get flu shots two years in a row.

It's also worth noting that 97 percent of the miscarriages in this study occurred in the first trimester, according to Dr. Donahue. Miscarriages are more likely to happen in the first trimester anyway, which makes it more difficult to be sure of exactly what these results mean, Jessica Shepherd, M.D., an assistant professor of clinical obstetrics and gynecology and director of minimally invasive gynecology at the University of Illinois College of Medicine at Chicago, tells SELF. "There are a lot of reasons why people miscarry, and we often have to rule out several possible reasons rather than just one cause," she says.

“Our study does not and cannot establish a causal association between the vaccine and miscarriage,” Dr. Donahue says.

That's partly due to the design of the study (the researchers were just observing trends rather than manipulating any variables). But it's also because "this is just one study and its results differ from all the other studies that have attempted to study miscarriage and influenza vaccination,” he explains.

Plus, the exact makeup of the flu vaccine changes from year to year. "When researchers make a flu vaccine, they find the most aggressive strains of the flu and make a new vaccine," Yvonne Bohn, M.D., an ob/gyn at Providence Saint John’s Health Center in Santa Monica, California, tells SELF. "Every year the flu vaccine is different." So, if you're still giving future flu vaccines the side-eye, remember that you won't be getting the same one used in the study.

Also, just as a reminder, this is a relatively small-scale study, including records for fewer than 1,000 women in total. In order to confirm any link here, many more studies with many more people would need to be performed.

As of now, experts still believe that the benefits of getting a flu vaccine during pregnancy far outweigh the possible risks.

When you’re pregnant, your immune system is already being taxed, Amesh A. Adalja, M.D., a board-certified infectious disease physician and affiliated scholar at the Johns Hopkins Center for Health Security, tells SELF. That means you’re more likely to get sick (and really sick) from an illness than you would be if you weren’t pregnant. “The flu is a deadly disease for pregnant women,” Dr. Adalja says. “The flu shot is protective—you have to weigh that against a single study that found a correlation.”

Plus, when flu season is especially bad, the risk of getting the illness when you’re pregnant is even higher—and things can go downhill fast, Christine Greves, M.D., a board-certified ob/gyn at the Winnie Palmer Hospital for Women and Babies, tells SELF. “Pregnant women have a much higher chance of needing to be in the ICU when they get the flu because they’re already at a disadvantage from being immunosuppressed,” she says. “That’s why we try to arm them with the vaccine.” Pregnant women are also more likely to get a serious bout of the flu that turns into pneumonia than women who aren't pregnant, women's health expert Jennifer Wider, M.D., tells SELF.

Getting the flu during pregnancy can also put your baby's health at risk: It increases your risk of miscarriage and preterm labor, Sherry Ross, M.D., an ob/gyn at Providence Saint John’s Health Center in Santa Monica, California, and author of She-ology: The Definitive Guide to Women's Intimate Health. Period., tells SELF.

The flu shot comes with an extra benefit for babies: If you get it during pregnancy, the vaccine can also protect a baby against the flu for up to six months of their life, Dr. Ross says. And, because it’s not recommended that babies get a flu shot before that time, getting your flu shot while pregnant is especially important for the future health of your baby.

But this doesn’t mean medical experts are totally blowing off these findings.

“I think they’re intriguing,” Dr. Adalja says. “What will have to happen now is to determine if this link is real.” Dr. Greves agrees that the findings need further investigation. “This does raise my eyebrows,” she says. However, every medical expert we spoke to agreed that it's still crucial to get the flu vaccine during pregnancy. "The dangers of getting the flu as a pregnant woman far outweigh this one study with inconclusive results," Dr. Wider says. "If I were pregnant, I would be getting the vaccine this flu season."

Dr. Donahue stresses that “there is a wealth of data supporting the safety of vaccine in pregnancy, especially later in pregnancy,” adding, “with additional study, we hope to better understand the association between miscarriage and repeated influenza vaccinations.”

If you’re pregnant and are nervous about getting a flu vaccine, talk to your doctor before making a decision. "It's important to have a discussion with your ob/gyn to really go through the risks and benefits of having the vaccine versus not having it, rather than just saying you choose not to have it," Dr. Shepherd says. You can also wait until after you're 12 weeks pregnant when your risk for a miscarriage is much lower, Dr. Bohn says. Either way, experts stress that you shouldn't write off the vaccine because of these findings—it could save your life.

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