Does The Flu Vaccine Cause Miscarriage? This New Study Seems Scarier Than It Is

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The United States is just a couple of weeks away from the unofficial start of influenza season, with many heading to their doctors' offices and local drug stores to receive their annual flu shot. For pregnant women, the concern about whether or not to get a flu shot can be a fraught decision, despite assurances from the Centers of Disease Control and Prevention that the flu shot is recommended for pregnant women during flu season, no matter how far along they are. Still, there are many pregnant women who wonder, “Does the flu vaccine cause miscarriages?” A new study published Wednesday in the journal Vaccine has raised that same question — and a surprising answer suggests that more research is needed.

The preliminary study found a small association between the flu vaccine and miscarriage, but the researchers have been very quick to note their findings are not a causal link. To reiterate: The flu vaccine does not cause miscarriages — but researchers have now heard the call to more closely examine the findings from Wednesday’s study. Speaking to The Washington Post, CDC senior adviser for vaccines Amanda Cohn emphasized the study's importance.

It’s important to understand that these findings are still preliminary, conducted from a study with a relatively small sample size. Researchers at Wisconsin’s Marshfield Clinic Research Institute compared two groups of pregnant women: each group consisted of 485 pregnant women aged 18 to 44. One group was exclusively women who had a miscarriage during the 2010-2011 and 2011-2012 flu seasons. The other group was women who had a normal delivery during that same time.

Here’s what the researchers found: Of the 485 women who had miscarriages, 17 had received a flu vaccine at least 28 days prior to their miscarriage, and also in the flu season prior. James Donahue, epidemiologist and lead author of the study, told The Washington Post, “We only saw the link between vaccination and miscarriage if they had been vaccinated in the season before.” The study did not examine what specifically caused this link in their findings, nor did it look at any flu seasons earlier that 2010 or later than 2012.

In a release on Wednesday, the American Congress of Obstetricians and Gynecologists responded to the study, urging pregnant women to talk to their health care providers about whether or not they should receive the flu vaccine. ACOG, along with the CDC and the study’s authors, continue to recommend that all women should receive the flu vaccine each year and that the flu vaccine is safe for pregnant women.

It’s especially important for pregnant women to get the flu vaccine as they can pass their antibodies on to their developing fetus, giving their babies protection from the flu for the first few months after they’re born. The flu vaccine is not given to babies younger than 6 months, so establishing immunity while in utero is highly beneficial.

The American Academy of Pediatrics recommends that children 6 months and older should receive the flu vaccine every year. As newborns can’t receive the flu vaccine, contracting influenza could become life-threatening, especially babies who may have underlying medical conditions such as diabetes, lung or heart diseases, or asthma — some of these conditions may not even have yet been diagnosed when a baby is younger than 6 months old, which increases the risk of deadly complications should such affected babies contract the flu. That’s what makes maternal immunization so important.

While the results of the study may sound the alarm for some pregnant women, the efficacy and safety of the flu vaccine during pregnancy has been well established. Edward Belongia, a senior epidemiologist at the Marshfield Institute told NBC News that their findings indicate there is room for more study. “What we have here is a signal." Belongia continued, "It’s not definitive. It might be wrong. I have no doubt that we will eventually sort this out and understand what’s going on, but that takes time.”

The best thing any pregnant woman can do this flu season is talk to her health care provider to find out when is the best time to get a flu shot, and best practices not to catch the flu — or any other fall and winter illness.