Flu symptoms can be more severe when you're pregnant, landing women in the hospital, threatening their lives and even leading to preterm birth or miscarriage. The virus is a risk to the woman and the baby.
So, it's particularly important that people who are pregnant get the flu vaccine. And it's also important that the effects of those vaccines be studied in pregnant women.
But research doesn't always turn up the information you're expecting, which is what happened last week when a study was published that found an association between the flu vaccine and early-term miscarriage in some women.
"We knew this would be controversial when it was published. This was an unexpected safety signal. This is not what we were looking for," says one of the study's co-authors, epidemiologist Dr. Edward Belongia. He directs the center for clinical epidemiology and population health at the Marshfield Clinic in Wisconsin, and is a member of the CDC's advisory committee on immunization practices.
"I believe," Belongia says, "the best approach with the public is to be very clear and open and transparent about 'Here's what we know; here are the limitations; here's why we still recommend the flu vaccine during pregnancy.' "