Researchers say they’ve discovered a potential association between the flu vaccine and miscarriage.
A new study, published this week in the journal Vaccine, is the first to identify this possible connection.
But, the authors are adamant that their findings are still too preliminary to establish a causal link between the two.
Nonetheless, many have taken note.
“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 (CDC), told The Washington Post.
What the study revealed
In the study, 484 women, ages 18 to 44, who’d had miscarriages during the 2010-2011 flu season were compared with 485 woman who had had normal deliveries during that same period.
The women were studied again during the 2011-2012 flu season.
In the group that miscarried, 17 had had a flu vaccination within 28 days of their miscarriages. They had also been immunized the prior year.
In the group of women who had had normal deliveries, only four had received the vaccine within the preceding 28 days. These four had also been immunized the prior year.
The only link appears to be between the flu vaccine and miscarriage in instances in which the woman had also been immunized the year before.
However, the results are at odds with other preexisting studies, and researchers note that the small sample size of the recent study could be problematic.
“The data from this study are inconsistent with numerous previous studies, including those carried out by the same group,” Cynthia Leifer, PhD, an associate professor of immunology at Cornell University, told Healthline.
The authors also emphasize that their study “does not and cannot establish a causal relationship.”
Having the flu while pregnant
Flu remains a serious health concern for pregnant women and their babies.
Expectant mothers are at increased risk of flu complications, including miscarriage, in addition to the possibility of having babies born with birth defects.
Additionally, the flu vaccine is not approved for use in newborns and infants younger than 6 months old.
The most effective way to protect them is through maternal vaccination.
As such, major health organizations in the United States, including the CDC and the American College of Obstetricians and Gynecologists (ACOG), have recommended that pregnant women receive flu vaccines.
Those organizations have also noted these new findings but have not deemed it necessary to change their recommendation.
“In evaluating all of the available scientific information, there is insufficient information to support changing the current recommendation which is to offer and encourage routine flu vaccinations during pregnancy regardless of the trimester of pregnancy,” said Dr. Haywood L. Brown, president of ACOG.
What could be the connection?
The study does not address why there may be a connection between miscarriage and flu vaccine, but there is some speculation.
Flu vaccines have changed dramatically in the past 10 years in response to concerns about global flu pandemics like the H1N1 swine flu outbreak in 2009, which killed hundreds of thousands of people.
Study authors speculate that their results could have something to do with pregnant women receiving the newer formulation of the vaccine two years in a row.
They stress, as do members of ACOG and the CDC, that even though current recommendations remain unchanged, there must be more research done on this important issue.