Study finds why some COVID-19 patients never regain sense of smell

An analysis olfactory epithelium with a biopsy-like approach found that COVID-19 patients with a prolonged loss of smell may have their nerve cells fallen victim to T cells.

A man is seen smelling champagne at a wine tasting session in France on April 14, 2021. (photo credit: PASCAL ROSSIGNOL/REUTERS)
A man is seen smelling champagne at a wine tasting session in France on April 14, 2021.
(photo credit: PASCAL ROSSIGNOL/REUTERS)

Why don't some people who suffered from COVID-19 ever get their sense of smell back? According to a new study, it may be due to a declining number of olfactory nerve cells caused by an ongoing immune assault.

The findings of this study, published in online in the peer-reviewed academic journal Science Translational Medicine, sheds light on an ongoing sensory consequence from the global pandemic.

The study was led by scientists from Duke Health and further examined the causes of several other symptoms of long COVID.

Sniffing out the truth: Why some COVID-19 patients never get their smell back

Of the millions of people who have contracted COVID-19 over the past two years, there have been many who have continued to suffer from symptoms long after the infection itself has subsided.

These symptoms range from fatigue, brain fog and heart palpitations. However, among the most prominent of these is the loss of a sense of smell, also known as asomnia.

 Anosmia or smell blindness, loss of the ability to smell, one of the possible symptoms of COVID-19. (credit: INGIMAGE PICTURES) Anosmia or smell blindness, loss of the ability to smell, one of the possible symptoms of COVID-19. (credit: INGIMAGE PICTURES)

It is unclear how persistent asomnia happens after infection with COVID-19, though there have been many theories. 

To figure this out, the researchers, led by Bradley Goldstein from Duke University and including experts from Harvard University and the University of California San Diego, conducted a biopsy-based approach to analyze olfactory epithelial samples, including from COVID-19 patients with long-term loss of smell.

This biopsy revealed an interesting finding regarding T cells.

T cells are the immune system's "long-term memory. They are a specific type of immune cell that essentially finds and kills infected cells and pathogens. 

The researchers found that the T cells are seemingly engaged in an autoimmune-like response in the nose, with the cells being inflamed in the part of the nose where the nerve cells for cells are located, the olfactory epithelium.

This area has very delicate tissue. Since whatever autoimmune-like response with the T cells that's happening here causes damage, it may cause the number of nerve cells to decline, which in turn would impair one's sense of smell.

Why this happens isn't clear. However, the fact that it is happening does make sense for why some people never get their sense of smell back.

In addition, this discovery also may reveal something else important: A path toward restoring the sense of smell.

The T cells are what is damaging the olfactory epithelium, which causes the number of nerve cells to decline. Knowing that means knowing what part of the body is being damaged and which cells are involved: Both of which are key to designing a treatment. 

In a statement, Goldstein made clear that this will help pave the way to repairing some of the damage, helped by the fact that the tissue neurons did still have some capacity to repair.

It is hoped that with these developments, Goldstein and his lab may be able to at least partially restore sent to these COVID-19 victims.