A new study led by researchers in Australia may change the way we understand the danger of flu during pregnancy. The prevalent theory has been that pregnancy decreases the woman’s immune response, leading to more severe flu complications. The new study, published in PNAS, flips this theory, suggesting instead a drastic over response—what the researchers call a “vascular storm.”
The finding is important because all pregnant women will be exposed to some part of flu season. Those who are infected with the flu virus are at higher risk for pneumonia and other lung and heart complications. Even though the flu virus itself does not cross into the placenta to affect the developing baby directly, the fetus is at higher risk from brain damage, low birth weight and preterm birth.
Study details: Using pregnant and nonpregnant mice, the researchers were able to show that the flu virus remained in the lungs of nonpregnant mice. In the pregnant mice, however, the virus passed from the lungs into the major blood vessels and spread through the circulatory system. This triggered a drastic immune response. The response caused inflammation in blood vessels that reduced their ability to dilate by about 70% to 80%.
This vascular storm is caused by immune-system proteins and white blood cells that flood blood vessels, causing the insides to swell and narrow. This reaction may explain why flu that does not cross into the womb still affects developing babies. It may drastically cut down their blood and oxygen supply. Vascular inflammation can also occur with preeclampsia (pregnancy hypertension) and with certain individuals suffering from COVID-19.
More studies are needed to understand why the vascular storm occurs. One theory is that the placenta releases proteins and fetal DNA into a mother’s circulatory system…foreign elements that put the immune response on high alert. Adding the flu virus may somehow tip the immune system into a drastic response. Further research will also be needed to confirm this response in humans, but vascular inflammation is being targeted by new drugs currently being tested.
Takeaway: For now, the best defense against the flu and a vascular storm during pregnancy is for pregnant women to get their flu shots.
Source: Study titled “Influenza A Virus Causes Maternal and Fetal Pathology Via Innate and Adaptive Vascular Inflammation in Mice,” by researchers at Royal Melbourne Institute of Technology University, Australia, published in PNAS.