Depression may intensify response to flu vaccine in pregnant women

Pregnant women with significant signs of depression may react more strongly to the seasonal flu vaccine than women with milder cases of the common mood disorder, according to a new study slated to appear in the journal Brain, Behavior, and Immunity. The study was small but carefully designed. Researchers had 22 pregnant women fill out questionnaires designed to measure depression. (Questions touched on a range of topics including appetite, mood, and sleep.) Then they took blood samples from each woman before giving her a seasonal flu shot. Six to nine days later, they collected a second vial of blood. To gauge how intensely the women's bodies reacted to the flu vaccine, researchers examined blood levels of MIF (macrophage migration inhibitory factor), a protein that promotes inflammation.

They found that, a week after the flu shot, women who scored highest on the depression scale had roughly twice as much MIF in their blood as women who scored the lowest, meaning their bodies mounted a greater inflammatory response to the vaccine. To be clear, the women didn't feel any different, say lead author Lisa Christian, PhD, a professor of psychiatry at Ohio State University. In other words, the only sign of greater inflammation was in the blood. "In the context of vaccination, this response isn't problematic," she says. "But when women with major depression get the flu, it can be a different story."

That's because depression + pregnancy delivers a one-two punch to the immune system. During a healthy pregnancy, the body downshifts the immune system to protect the fetus. And for anyone—pregnant or not—major depression hobbles the immune system by putting chronic, low-grade stress on the body. That's why it's so important for depressed pregnant women to get a seasonal flu shot, says Christian. Their stressed-out immune system puts them at greater odds of having flu-related complications, such as pre-term labor and gestational hypertension. Overall, roughly 13% of pregnant women suffer from depression, according to the National Women's Health Information Center. And, although the numbers are difficult to quantify, as many as 25% of those women may have major depression.

Despite annual public health recommendations that all pregnant women receive seasonal flu shots, only an estimated 12 to 13 % of pregant women in the U.S. have done so in recent years, according to the Centers for Disease Control and Prevention (CDC). "I'll be interested to see how that might change this year," said Christian, in light of the emphasis on pregnant women getting the 2009 HINI flu vaccination. Although her study didn't include the new 2009 H1N1 vaccine, there is no reason to believe the women's inflammatory response would be different, she says.