The majority of people—about 80% according to research—only suffer mild symptoms with COVID-19. Others may require hospitalization—but for some patients, the new coronavirus can be deadly.

One life-threatening complication that can arise from the new coronavirus is acute respiratory distress syndrome, commonly referred to as ARDS. And new research from the Journal of the American Medical Association (JAMA) suggests that more than 40 per cent of individuals in the study hospitalized for severe and critical COVID-19 developed ARDS—and over 50% of those diagnosed died from the disease.

What exactly is ARDS?

The American Lung Association (ALA) says ARDS is a rapidly progressive disease that can occur in critically ill patients—most notably now, in those diagnosed with severe illness resulting from coronavirus.

ARDS is sometimes initially diagnosed as pneumonia or pulmonary edema (fluid in the lungs from heart disease), and, per the ALA, those with ARDS often have severe shortness of breath, cough, and fever. Fast heart rate and rapid breathing also shows up in ARDS patients, along with chest pain, particularly during inhaling. “ARDS is manifested as rapid and progressive shortness of breath,” Shervin Takyar, MD, PhD, a Yale Medicine pulmonologist, tells Health.

The disease can be caused by direct injuries to the lungs (pneumonia, aspiration, near drowning, or smoke inhalation), or indirect injuries to the lungs (sepsis, blood transfusions, or medication reactions). While many still won’t develop ARDS even with those injuries, some risk factors—like a smoking history, oxygen use, obesity, and recent chemotherapy—can increase a person’s risk of developing the disease.

In most cases of ARDS, patients will have to be supported by supplemental oxygen and mechanical ventilation soon after the start of their symptoms, says Dr. Takyar. In some cases, if inflammation and fluid in the lungs persists, some ARDS patients will develop scarring of the lungs (the fibrotic stage of ARDS). In others, the lung or lungs can eventually pop and deflate, leading to a pneumothorax or a collapsed lung.

Similar to many other viruses, coronaviruses—including the novel coronavirus, or SARS-CoV-2—can infect and damage the lung cells, setting the stage for the occurrence of ARDS, explains Dr. Takyar. “It is thought that the infection-induced damage and inflammation cause a malfunction of the lung vasculature [the pulmonary vessels within the lungs],” he says. When that happens, the exchange of oxygen within the body is impaired. Among viruses, the ones that cause pneumonia (like COVID-19) are more likely to cause ARDS.

When patients are in the late stages of novel coronavirus infection—after severe damage has already been done to their lungs—their body will try to fight off the virus by sending immune cells to the lungs, which is what ultimately causes the inflammatory reaction, explains Dr Takyar. In fact, ARDS in coronavirus “seems to be less directly due to the virus itself and more related to inflammation, or the body’s response to the virus,” adds Jaimie Meyer, MD, a Yale Medicine infectious disease specialist.

While experts are still in the early stages of learning about COVID-19, research surrounding ARDS and coronavirus has found that the two often go hand-in-hand. According to the earlier JAMA study, researchers also concluded that an older age translated to a higher risk factor of developing ARDS and dying, “likely owing to less rigorous immune response,” per the study authors. Additionally, the authors noted that if an ARDS patient was running a higher fever, they were more likely to recover, due to the body fighting off the infection.

An alternate study published in January in peer-reviewed journal The Lancet also found that ARDS can develop incredibly quickly in critically ill coronavirus patients. Those researchers found that ARDS developed in 17% of those diagnosed COVID-19, among whom, 11 worsened in a short period of time and died of either ARDS or other serious complications like multiple organ failure.