New Research Finds That Pregnant Women’s Immune Response Heightened By Flu During Pregnancy

It has long been thought that the immune responses of a pregnant woman’s body were thought to be weakened, so as to prevent the body from rejecting the fetus. However, a brand new study published in the Proceedings of the National Academy of Sciences, found that a pregnant woman’s immunological response is actually turned up, instead of down by the flu during pregnancy. This could explain why pregnant women get sicker than other normally healthy adults during flu season.

sick pregnant mama

Though the study was small, examining 21 pregnant women and 29 non-pregnant healthy women, the results were significant. Catherine Blish, MD, PhD, the study’s senior author and assistant professor of infectious diseases said, “We were surprised by the overall finding. We now understand that severe influenza in pregnancy is a hyperinflammatory disease rather than a state of immunodeficiency. This means that treatment of flu in pregnancy might have more to do with modulating the immune response than worrying about viral replication.”

Researchers studied immune cells taken from both groups of women. The cells were exposed to various different flu viruses in the laboratory. The samples had been collected by obtaining blood samples from the women both before and seven days after they had received their flu immunizations. Samples were also obtained from pregnant women six weeks after they had delivered their babies. The researchers also made a point to study responses to two specific flu viruses; H1N1, which was responsible for the 2009 pandemic, and a strain of seasonal flu, H3N2.

The researchers found that pregnancy actually enhances the immune response of two specific types of white blood cells, including T cells and natural killer cells, in response to H1N1. When compared against the same cells from the women who were not pregnant, the H1N1 strain caused the pregnant women’s T cells and natural killer cells to produce more chemokines and cytokines, which are molecules that help to draw in other immune cells to an infection site. Blish says, “If the chemokine levels are too high, that can bring in too many immune cells. That’s a bad thing in a lung where you need air space.

Blish also noted that contracting the flu while pregnant, especially the pandemic strains such as those from the years 1918, 1957 and 2009, carry an increased risk of contracting pneumonia or even death. Both of the flu strains also caused T cells and natural killer cells to be triggered in a larger array of ways in women who are pregnant, versus non pregnant women. In this day and age, pregnant women who have contracted the flu are typically treated with drugs that are meant to slow the replication of the virus in their bodies. While this can be a useful treatment, the results of this study suggests that there may be other good treatment options, as well.

Alexander Kay, MD, the study’s lead author and an instructor in pediatric infectious diseases says, “If our finding ends up bearing out in future studies, it opens the possibility that we can develop new immune-modulating treatment approaches in the setting of severe influenza, especially in pregnant women.” Blish adds, “I wonder if this is an inflammatory pathway that is normally activated later in pregnancy to prepare the body for birth, but that flu happens to overlap with the pathway and aberrantly activates it too early.”

Both Kay and Blish intend to continue their research by studying non-pregnant and pregnant women who have contracted the flu, in their day-to-day lives. Both researchers also hope that this research will remind women who are planning to get pregnant or who already are, to be sure to receive their flu immunizations. Kay said, “Flu vaccination is very important to avoid this inflammatory response we’re seeing. But only 50 percent of pregnant women are currently vaccinated for influenza.



About the author


Jennifer is a stay-at-home mom who spends her days chasing around the never-ending ball of energy that is her son. By night you can find her at her computer, drafting up her next great blog post about parenting with chronic illnesses. She is also an avid photographer and jewelry artisan.

She is the founder of the Fibromyalgia support website,, where Fibromyalgia patients can go to gain support, learn how to advocate for themselves, and spread awareness of this still relatively unheard of condition.

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