Study Shows Link Between Flu Vaccine And Miscarriage

September 14, 2017
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Researchers who are studying the flu vaccine in pregnancy have found that there’s a hint of a possible link between miscarriage early in pregnancy and the flu vaccine in women who received a certain version of the vaccine two years in a row.

It’s the first study was to identify a potential link between miscarriage and the flu vaccine and the first to assess the effect of repeat influenza vaccination and risk of miscarriage. The findings suggest an association, not a causal link, and the research is too weak and preliminary, experts say, to change the advice, which is based on a multitude of previous studies, that pregnant women should get a flu vaccine to protect them from influenza, a deadly disease that may cause serious birth defects and miscarriage.

However the study is likely to raise questions about the safety of the vaccine as flu season gets underway.

“I think it’s really important for women to understand that this is a possible link, and it is a possible link that needs to be studied and needs to be looked at over more [flu] seasons,” said Amanda Cohn, senior adviser for vaccines at the Centers for Disease Control and Prevention, which funded the study.

“We need to understand if it’s the flu vaccine, or is this a group of women [who received flu vaccines] who were also more likely to have miscarriages,” she said.

Medical officials say they understand that the information may be of concern to pregnant women. They advised pregnant  to speak to their health-care providers for the most accurate information and to determine the best timing for a flu shot.

Currently, the CDC, the American College of Obstetricians and Gynecologists and the study authors continue to recommend that pregnant women get a flu vaccine during any stage of pregnancy because of the danger influenza poses to women and their developing babies.

Experts say that vaccination during pregnancy is also the most effective strategy to protect newborns, because the flu vaccine is not approved for use in infants younger than six months.

Anticipating questions from health-care providers and pregnant women, the CDC on Tuesday posted  about influenza vaccination during pregnancy.

Many previous studies have indicated that flu vaccines can be given safely during pregnancy including numerous studies that found no link between flu vaccination and miscarriage.

The new findings were part of an observational study published Wednesday in the journal Vaccine. The researchers who conducted the study however, emphasize that it is not a reason to avoid the flu vaccine, even for pregnant women.

“Science is an incremental process, and a lot of people don’t understand that very seldom does a single study provide a definitive answer that can lead to changes in recommendations,” said Edward Belongia, a senior epidemiologist at the Marshfield Clinic Research Institute in Wisconsin and one of the study authors.

Scientists compared 485 pregnant women, ages 18 to 44, who had a miscarriage to 485 pregnant women of similar ages who had normal deliveries during the flu seasons of 2010-2011 and 2011-2012. Of the women who miscarried, 17 received flu vaccine in the 28 days before the miscarriage, and had also been immunized the prior flu season. Most  of the miscarriages occurred in the first trimester, but several occurred during the second trimester. The median age of the fetus at time of miscarriage was 7 weeks.

By comparison, of the women who had normal deliveries, 4 who had received the flu vaccine in the preceding 28 days had also been vaccinated during the previous flu season.

“We only saw the link between vaccination and miscarriage if they had been vaccinated in the season before,” said James Donahue, an epidemiologist and lead author.

Since 2004, the CDC and other organizations have recommended routine flu vaccination for pregnant women regardless of their stage of pregnancy.


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