New research involving Irish scientists has revealed why flu can be devastating for pregnant women.

According to the findings, during pregnancy, flu spreads from the lungs through the blood vessels into the circulatory system and this triggers a damaging hyperactive immune response.

Currently in Ireland, pregnant women are considered to be one of the ‘at risk' groups for flu and they are recommended to get the flu vaccine.

The research, which was carried out in animal models, was led by a team at RMIT University in Australia, who worked in collaboration with other Australian universities, along with researchers and clinicians from Trinity College Dublin (TCD).

According to TCD, this pre-clinical study "has overturned current scientific thinking on the reasons why flu infections affect pregnant women and their babies so severely", and marks a "landmark advance" in our understanding of viral infections and 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," commented Prof John O'Leary of TCD.

The study's lead author, Dr Stella Liong of RMIT University, noted that these findings suggest that the vascular system is key to potentially devastating complications caused by flu during pregnancy.

"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. 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," she explained.

She said that the inflammation they discovered in the circulatory system is so overwhelming, "it's like a vascular storm wreaking havoc throughout the body".

"We need further research to clinically validate our findings, but the discovery of this new mechanism is a crucial step towards the development of flu therapies designed specifically for pregnant women," Dr Liong noted.

In this new study, the researchers found that pregnant mice with flu had severe inflammation in the large blood vessels and the aorta.

While a healthy blood vessel dilates 90-100% to let blood flow freely, these flu-infected blood vessels functioned at only 20-30% capacity.

According to the study's lead investigator, Associate Prof Stavros Selemidis of RMIT University, even a small change in the diameter of a blood vessel could lead to major changes in blood flow.

"We found a dramatic difference in these inflamed blood vessels, which can seriously affect how much blood makes it to the placenta and all the organs that help support the growing baby.

"We've known that flu infection in pregnancy results in an increased risk of babies being smaller and suffering oxygen starvation. Our research shows the critical role that the vascular system could be playing in this, with inflammation in the blood vessels reducing blood flow and nutrient transfer from mum to baby," he explained.

The researchers also pointed out that their findings could have implications for our understanding of how the COVID-19 virus could be affecting the vascular system.

"Flu and coronavirus are different but there are parallels and we do know that COVID-19 causes vascular dysfunction, which can lead to strokes and other cardiovascular problems.

"Our studies in pregnancy offer new insights into the fundamental biology of how respiratory viruses can drive dysfunction in the vascular system. This could be valuable knowledge for those scientists working directly on treatments and vaccines for COVID-19," Dr Liong added.