Immune system overreaction linked to deadly flu in pregnancy

Posted on: 19 May 2026

In most people, influenza stays in the upper respiratory tract – mainly the nose – and clears without spreading further. But during pregnancy, the virus can extend beyond the lungs into the cardiovascular system, increasing the risk of severe complications for mothers and babies.

Now a new preclinical study using animal models reveals precisely why the virus can spill into the bloodstream during pregnancy, opening the door for targeted treatment. The study is a bilateral partnership between Trinity College Dublin, with collaborators from RMIT University and the University of Adelaide and is published in Science Advances.

Researchers identified a viral sensor in the immune system, known as TLR7, that can become overactive during pregnancy, amplifying inflammation and spreading disease into the bloodstream.

Blocking TLR7 could help prevent the harmful inflammation that makes flu in pregnancy so dangerous. This work can help protect developing babies by stopping the placenta from becoming overly inflamed during flu infection.

Professor John O’Leary, School of Medicine, Trinity, said: “This international research is of high impact in relation to our understanding of viruses and pregnancy and the role of the maternal immune response.”

What is the potential impact of this research? 

Earlier studies from RMIT have shown that severe flu in pregnancy can have long‑term impacts on babies’ brain development, by inflaming blood vessels and reducing the flow of oxygen and nutrients from mother to baby.

This new study pinpoints the underlying cause of that damage, reshaping our understanding of flu‑related risk in pregnancy and opening the door to more targeted therapies.

RMIT co-lead author, Prof. Stavros Selemidis, said future treatments could focus on the immune system rather than the virus itself.

“Our study shows that in pregnancy, the problem isn’t just the flu virus – it’s the immune system overreacting. That’s where future treatments could really make a difference," he explained.

“We’re ready to work with partners to help develop the next generation of therapies and clinical guidelines.”

Next steps for this work: The team is planning further research on how to target TLR7 to reduce the risk of severe influenza and pregnancy complications.

You can read the paper: ‘TLR7 alters the maternal immune landscape during influenza A infection to increase maternal and fetal morbidity’, on the Science Advances website.

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