Pregnant women with significant symptoms of depression tend to have a stronger biological reaction to the seasonal flu vaccine than do women with lower depression levels, according to a new study.
The finding provides an argument in favor of flu vaccination during pregnancy, researchers say, because it suggests that the immune systems in depressed pregnant women are not functioning typically. This immune dysregulation could affect symptom severity among women who become infected with influenza.
Previous studies have established a link between some preterm births and gestational high blood pressure cases and infection or inflammation. Avoiding the flu with a safe vaccine might be one way to lower the chances of complications, according to researchers.
An internal inflammatory response to vaccination is not uncommon - it's an essential part of the process the immune system initiates to prepare for a successful fight against an actual infection. But it's also expected to be a weak and brief response.
"Inflammatory responses to vaccination do no harm, are mild, and typically go away within a few days. But an extended inflammatory response to vaccination, such as the one seen in women with the most depressive symptoms, isn't expected, and it serves as a way to estimate how somebody might respond to an actual infection or illness," said Lisa Christian, an assistant professor of psychiatry at Ohio State University and lead author of the research.
Despite public health recommendations that pregnant women get seasonal flu shots, only an estimated 12 percent to 13 percent of pregnant women in the United States have done so in recent years, according to the Centers for Disease Control and Prevention (CDC).
"It will be interesting to see how that might change this year," said Christian, in light of CDC recommendations that pregnant women receive both seasonal and H1N1 flu vaccinations.
Christian's study appears online and is scheduled for print publication later in the journal Brain, Behavior, and Immunity.
She and colleagues also recently published a study in the same journal indicating that pregnant women experiencing depressive symptoms and certain stressors had higher levels of inflammatory markers in their blood than did pregnant women with lower depression and stress levels.
Though this mind-body connection is well established in people with chronic stress, Christian said few studies have examined the effects of depression and stress during pregnancy. Research has shown that pregnancy suppresses certain functions of the immune system to prevent rejection of the fetus and to protect the fetus from inflammation that accompanies fevers and other illnesses.
"Our basic starting question was, do those same relationships between depression and immune function hold during pregnancy?" said Christian, also an investigator in Ohio State's Institute for Behavioral Medicine Research. "And these studies suggest that they do. We see immune dysregulation during pregnancy due to stress and depression."
In the flu vaccine study, 22 pregnant women completed questionnaires about their depressive symptoms and gave blood samples before they received a seasonal influenza shot. Between six and nine days later, a second round of blood samples was collected.
Researchers assessed the women's depressive symptoms using the Center for Epidemiologic Studies Depression Scale, a series of 20 questions about physical, emotional and cognitive symptoms. The women were classified in three groups: having either no or minimal depression; mild or moderate depressive symptoms; and significant depressive symptoms. A diagnosis of depression can be made only after an interview with a doctor.
The scientists analyzed the post-vaccination blood samples for the presence of macrophage migration inhibitory factor, or MIF, a protein that promotes inflammation by suppressing other substances in the blood that fight inflammation.
A week after receiving the flu shots, the women with the highest scores on the depression scale had about twice as much MIF in their blood as did women reporting minimal symptoms.
"The more depressive symptoms the women had, the more MIF they had after vaccination," Christian said. "In the context of an actual illness, the response would be expected to be much more robust and more extended. And then we might have concerns about whether women who show an exaggerated inflammatory response would be more susceptible to complications."
Christian's previous study on inflammatory markers in the blood during pregnancy involved 60 women, including the 22 who participated in the flu study.