Since the start of the pandemic in 2020, experts have been upfront regarding the common symptoms of COVID-19. One of them is the loss of smell, which goes hand in hand with the loss of taste. In most cases, patients recover both senses after their bout with the initial infection. However, some continue to suffer smell loss long-term.

In a new study published in the journal Science Translational Medicine last week, scientists possibly uncovered why some people fail to recover their sense of smell despite overcoming SARS-CoV-2 infection. Though their research focused on the loss of smell, the findings seemingly shed light on other long COVID symptoms with a similar mechanism, including fatigue, shortness of breath and brain fog.

The team analyzed olfactory epithelial samples collected from 24 biopsies. Nine samples were from patients who had long-term smell loss after COVID-19. Despite the absence of detectable SARS-CoV-2 RNA or protein, researchers identified what was causing the long-term problem in the olfactory cells.

Scientists found that there seemed to be an immune assault on olfactory nerve cells and a decline in the number of those cells. In addition, T cell-mediated inflammation was also present in the olfactory epithelium long after the virus had been eliminated from the tissue.

"The findings are striking. It's almost resembling a sort of autoimmune-like process in the nose," senior author Bradley Goldstein, M.D., Ph.D. said in a press release. He is an associate professor in Duke's Department of Head and Neck Surgery and Communication Sciences and the Department of Neurobiology.

Goldstein noted that their study was a key step toward designing better treatments for the issue because they now have information on which sites get damaged and which types of cells are involved in long-term loss of smell. But more research needs to be done first.

"We are hopeful that modulating the abnormal immune response or repair processes within the nose of these patients could help to at least partially restore a sense of smell," he said.

In May, a study published in SAGE Journals reported decreasing incidence of chemosensory disruptions with the newer coronavirus variants. This led some scientists to surmise that loss of smell was becoming less common as a symptom of COVID-19 as the virus continues to evolve.