Pregnancy and the Flu: A Vascular Storm?

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Researchers are still learning about the effects of COVID-19 on pregnancy and on babies born to mothers infected with the virus. You can read a good update here. They have had a longer time to study the effects of influenza virus in pregnancy.

A new study published in the prestigious journal Proceedings of the National Academy of Sciences, is a reminder that flu during pregnancy is a serious disease for moms and babies. It also upends the understanding of how flu effects pregnancy and developing babies. In fact, flu during pregnancy may act a bit like COVID.

If you are pregnant, you can’t avoid at least part of the flu season. Pregnant women are more likely to experience complications like flu-related pneumonia and acute respiratory distress. Effects on pregnancy include growth restriction, preterm birth, and loss of pregnancy. Flu during pregnancy has also been linked to cerebral palsy, seizures in newborns, and even an increased risk for schizophrenia and heart disease in children born to flu-infected moms years later. In short, you want to avoid flu in pregnancy.

Up till now, researchers have assumed that complications from flu during pregnancy are due to a lower immune response caused by pregnancy. The theory is that because you are growing a new person inside your womb, with different proteins and DNA, your immune system becomes less alert. This keeps your immune system from overreacting to these “foreign” substances. The relaxed immune system puts you at higher risk from the flu. You get sicker because you don’t fight it well.

The effects on developing babies has been blamed on overall weakness from the infection. We know it is not a direct effect of the virus because, unlike Zika, flu virus does not cross the placenta. The jury is still out on COVID passing through the placenta. Researchers at Royal Melbourne Institute of Technology University in Australia may have changed the way we understand the danger of flu during pregnancy. In fact, it may not be a relaxed immune system. It may be a drastic immune system over reaction.

Using pregnant and nonpregnant mice, the researchers were able to show that flu virus remains in the lungs of the nonpregnant mice. However, in the pregnant mice, the virus passes from the lungs into the major blood vessels leaving the lungs and disperses through the circulatory system. Viral spread through the circulation triggers a drastic immune response that causes enough inflammation in blood vessels to decrease their ability to open (dilate) by about 75 percent.

The researchers call this response a “vascular storm.” Immune system proteins and white blood cells flood blood vessels causing the inside of blood vessels 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. This reaction is similar to the reaction of the immune system seen in some people with COVID-19. A similar type reaction is also seen in women develop toxemia of pregnancy.

The researchers will need more studies to understand why the vascular storm occurs. One theory is that when the placenta releases proteins and fetal DNA into a mothers circulation the mothers immune system does react to these substances as foreign invaders and goes on stand-by alert. Adding flu virus coursing through the circulatory system may somehow tip the immune system into a drastic response.

It will also take further research to confirm this response in humans, but vascular inflammation is being targeted by new drugs currently being tested for disease like COVID. They may someday be repurposed to treat flu also. For now, the best defense against the flu and a vascular storm in pregnancy is for pregnant women to get their flu shots.

Christopher Iliades
Dr. Chris Iliades is a medical doctor with 20 years of experience in clinical medicine and clinical research. Chris has been a full time medical writer and journalist since 2004. His byline appears in over 1,000 articles online including EverydayHealth, The Clinical Advisor, and Healthgrades. He has also written for print media including Cruising World Magazine, MD News, and The Johns Hopkins Children's Center Magazine. Chris lives with his wife and close to his three children and four grandchildren in the Boston area.

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