Study: Immune system overreaction explains why flu can be dangerous during pregnancy

A team of researchers from RMIT University has identified the mechanism by which flu can cause severe complications during pregnancy. According to the study, it is not the flu virus itself that directly affects the fetus, but the excessive response of the mother's immune system, which can disrupt the functioning of blood vessels and the placenta. The discovery, published in the prestigious journal Science Advances, could pave the way for new treatments designed to reduce the risks for pregnant women and their children.

• An immune sensor that becomes hyperactive

Researchers have identified an immune system receptor, called Toll-like receptor 7 (TLR7), which detects the genetic material of viruses. During pregnancy, this "sensor" can become overactive, triggering a strong inflammatory reaction. Instead of limiting the infection to the upper respiratory tract, the body mounts a response that affects blood circulation and can cause inflammation of the placenta, reducing the supply of oxygen and nutrients to the fetus.

• Placenta, affected by inflammation

The study authors showed that blocking TLR7 could prevent excessive inflammation of the placenta and protect fetal development during influenza infections. "These findings change the understanding of how respiratory viruses affect pregnancy," explained Stella Liong, the study's lead author.

According to the researcher, the negative effects are not caused by the virus passing to the fetus, but by "a hyperactive maternal immune response, which disrupts vascular function."

• Why is the flu more dangerous during pregnancy

Pregnant women are considered a group at increased risk of influenza complications, because hormonal and immune changes associated with pregnancy can favor severe forms of the disease. Complications can include: Pneumonia; respiratory failure; premature birth; intrauterine growth restriction; in severe cases, miscarriage.

Specialists emphasize that influenza vaccination is the most effective method of preventing severe influenza during pregnancy. Numerous studies have shown that vaccination is safe for the mother and fetus and also provides protection to the newborn in the first months of life. Organizations such as the World Health Organization and the Centers for Disease Control and Prevention recommend immunizing pregnant women in any trimester of pregnancy, during the influenza season.

• A possible new therapeutic target

The discovery of the role of TLR7 offers a promising direction for the development of therapies capable of tempering the excessive inflammatory reaction without compromising the body's antiviral defense. If these results are confirmed by clinical trials, doctors may have specific treatments in the future to protect pregnancy in the event of severe influenza infections. The results of the study are particularly important for Australia, where the influenza season coincides with the austral winter and begins in May-June. In the context of intense circulation of respiratory viruses, the research provides solid biological explanations for the firm recommendation of vaccination of pregnant women. The main message of the scientists is clear: during pregnancy, the flu should not be treated like a simple cold, and prevention by vaccination remains the safest and most effective method of protection for mother and child.