Pregnant women who get a flu vaccine in the first trimester might have an increased risk of miscarriage, according to a new study by researchers at the Centers for Disease Control and Prevention (CDC).
Even so, the CDC said that pregnant women should still get a flu vaccine because they are more likely to be hospitalized with a severe influenza illness than non-pregnant women.
The study was published in journal Vaccine on September 13, and conclusions were based on data from nearly 1,000 women.
The study discovered that women who received a flu vaccine containing the swine flu component (H1N1-pdm09) were more likely to have a miscarriage within 28 days — but only if they had received the same flu vaccine in the previous year.
In other words, women who experienced miscarriages between 2010 and 2012 were more likely to have received back-to-back flu shots.
The study identified a correlation, which does not mean that the flu vaccine actually caused any miscarriage, but the findings are still concerning. It is possible that pregnant women had an immunological response to receiving identical H1N1 vaccines two years in a row.
Unfortunately, there is not enough data to know whether the flu shot is risky in the first trimester. Flu shots are generally believed to be safe during pregnancy, but there is very little data on the risk of miscarriages in the first trimester, which was what prompted the study.