A group of scientists from Duke University Medical Center in the United States said that the reason why some people failed to restore their sense of smell after being infected with COVID-19 was related to the continuous immune attack on olfactory nerve cells and the reduction of the number of related cells. This discovery was published online on the 21st in the journal Science Translational Medicine, which provides an important perspective for people to solve this thorny problem that puzzles millions of COVID-19 infected people. While focusing on the loss of smell, this discovery also revealed the potential causes of other "long-term COVID-19" symptoms, including general fatigue, shortness of breath and brain fog, which may be caused by similar biological mechanisms. One of the first symptoms usually associated with COVID-19 infection is loss of smell, researchers said. Many people with olfactory changes in the acute phase of viral infection will recover within one to two weeks, but some people will not, which requires a better understanding of why these people will lose their sense of smell for months to years after infection with COVID-19. The joint research team, including Duke University, Harvard University and the University of California, San Diego, analyzed olfactory epithelium samples collected from 24 biopsy tissues, including 9 patients with long-term olfactory loss after obtaining the COVID-19. This biopsy based method reveals the extensive infiltration of T cells involved in the inflammation of olfactory epithelium, which is the tissue where olfactory nerve cells are located. Although no virus titer level reaching the diagnosis of COVID-19 has been detected, this unique inflammatory process still exists. In addition, the decrease in the number of olfactory sensory neurons may be due to the destruction of fragile tissues by persistent inflammation. The researchers said, "This is almost like an autoimmune process in the nose." The researchers are encouraged that even after a long-term immune attack, neurons seem to maintain a certain repair ability. The researchers hope that regulating the abnormal immune response or repair process in the nose of these patients can help at least part of the olfactory recovery. (Outlook New Times)