New Study Finds No Connection Between Flu Shots and Miscarriage

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A recent report released by the Advisory Committee on Immunization Practices says that there’s no link between flu shots and miscarriages.

The study focused on flu seasons from 2012 to 2015, studying each season individually and together, CNN reports:

The new study matched 1,236 pairs of women: in each pair one of the women had miscarried between 6 and 19 weeks; the other woman, or control, had given birth.

The women were also matched on whether they had been vaccinated in the previous season, creating 627 pairs who had been vaccinated in the previous season and 609 pairs who were not. The greater numbers allowed the study to detect an association with odds ratio of 1.6 or greater.

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An earlier, smaller study around the 2010-11 and 2011-12 flu seasons raised concerns about flu shots containing a vaccine against the H1N1 virus, according to STAT:

Some pregnant women who got flu shots did appear to be at higher risk of miscarrying, but only those who got vaccinated in the 28 days before their miscarriage — and in the previous year as well. Women who were only vaccinated in the year of their pregnancy didn’t appear to be at an increased risk.

However, that study was observational and based on the data of just 485 people. There were only 14 subjects who had been vaccinated two consecutive years and experienced miscarriages. The new study included three times the number of subjects and found no link between flu shots and miscarriages, leading Dr. Edward Belongia, head of the Center for Clinical Epidemiology and Population Health at Wisconsin’s Marshfield Clinic, to speculate that the previous association may have been the result of a “statistical fluke.”

Epidemiologists strongly urge pregnant people to get flu shots, citing increased risk of hospitalization and even death for those who forgo them, not to mention the fact that vaccines can also protect the health of the infant:

“There’s lots of evidence of the severity of flu for a pregnant woman, more chance of hospitalization, more risk of death, especially as she enters the second and third trimester,” lead investigator for the study James Donahue, a senior epidemiologist at Marshfield said. “There are also many studies that show the mother’s vaccination will help protect the newborn baby from flu, which is critical since the baby cannot be vaccinated until 6 months of age.”

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