As the annual flu season is underway, it is critical to acknowledge the severity of influenza (flu) viruses. Viruses infect, or hijack, cells and use them to produce even more viruses. The body then reacts to try to clear out the hijackers. The flu is primarily transmitted through respiratory droplets produced when an infected person talks, coughs, or sneezes. Influenza symptoms include fever, body aches, chills, headache, nausea, vomiting, dry cough, runny nose, and sore throat.  

The flu infects millions of people each year. However, some populations are even more susceptible to complications caused by the flu. Flu complications arise when the flu virus weakens the immune system and opens the door to secondary infections such as pneumonia, encephalitis, meningitis, and seizures. Vulnerable populations include young children, the elderly, anyone with chronic, heart, or immune conditions, and pregnant women.  

Pregnant women are at a high risk of flu complications that are detrimental to their health and the health of their fetuses. A recent study from 2022 describes the complications that arise from inflammation, the defense mechanism to fight the infection, since the flu virus can activate an exaggerated defensive inflammatory response. The research article explains vascular inflammation in particular. Vascular inflammation is characterized by blood vessel inflammation, leading to thickening and possible narrowing of vessel walls. This restriction in blood flow may cause damage to organs and tissue, which can cause less creation of blood vessels and less oxygen reaching the fetus. A “vascular storm" triggered by a flu infection during pregnancy is a mechanism that creates short and long-term cardiovascular complications because of the immune system’s intense assault of immune cells.  

The research showed that pregnancy-related adaptations in the immune and cardiovascular systems result in delayed post-viral infection recovery. In other words, the effects of pregnancy make it take longer for the body to recover from an infection. The exact biological mechanisms are unclear, but it is known that the slow clearing of the virus from the lungs during pregnancy involves overactive immune responses. In an alternative pathway, the hormone progesterone, which is increased during pregnancy, can cause harm during a flu infection. Progesterone relaxes the body and lets the influenza virus travel deeper into the lungs.  

The prolonged inflammatory reaction contributes to increased disease severity and widespread inflammation throughout the body. Additional maternal complications of flu during pregnancy include acute cardiopulmonary distress syndrome, which means the body does not receive enough oxygen for the organs to function properly. The complications for the fetus include intrauterine fetal growth restriction (FGR), where the baby is born small, and preterm labor. FGR also can cause birth defects like cleft lip or palate and congenital heart defects. There could also be neural tube defects, which are problems with the spinal cord and brain formation. There are also increased risks of long-term effects on the unborn child such as an increased risk of schizophrenia and other neurological disorders.  

Commonplace flu infections can have frightening consequences. This has prompted ongoing clinical research into developing additional antiviral treatments and exploring ways to manage influenza with over-the-counter medications. More research is needed into the exact mechanisms of how influenza affects the placenta and fetus on a cellular level.