Why is the Flu Dangerous for Pregnant Women?

A new preclinical study has revealed just how dangerous the flu can be for pregnant women, with findings suggesting the virus not only infects the lungs but also spreads to other areas of the body. Working from RMIT University, the team of researchers say the study could help explain why pregnant women with influenza often suffer from potentially fatal complications. The study could also offer new insight into how COVID-19 infects the lungs, spreads throughout the body and compromises the vascular system.

A hyperactive response

The team used animal models to map the progression of the flu in pregnant women. They noticed that as well as infecting the lungs the virus infiltrates the circulatory system through blood vessels. This sends the immune system into overdrive and triggers a potentially life-threatening state of hyperactivity. The findings were published in the Proceedings of the National Academy of Sciences and explain how inflammation in the vascular system can lead to dire outcomes for pregnant women.

“We've known for a long time that flu can cause serious maternal and foetal complications, but how this happens has not been clearly understood," says Dr Stella Liong, lead author of the study and a Vice-Chancellor's Postdoctoral Fellow at RMIT. “Conventional thinking has blamed the suppressed immune system that occurs in pregnancy but what we see is the opposite effect - flu infection leads to a drastically heightened immune response.”

Flu virus triggers a “vascular storm”

Not only are pregnant mothers who contract influenza more likely to be hospitalised with complications such as pneumonia, their babies are also at risk. Miscarriages, foetal growth restriction and preterm births are just some of the issues linked to influenza during pregnancy.

“The inflammation we found in the circulatory system is so overwhelming, it's like a vascular storm wreaking havoc throughout the body,” adds Liong.

Moving forward, Liong hopes the research can be used to develop specialist influenza therapies targeting pregnant women. Co-author Professor John O'Leary of Trinity College Dublin agrees, saying the study is a leap forward for scientists attempting to understand how viral infections, including COVID-19, impact pregnancy.

“The discovery of an influenza-induced 'vascular storm' is one of the most significant developments in inflammatory infectious diseases over the last 30 years and has significant implications for other viral infections, including COVID-19," says O’Leary.

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