Scientists are working to determine the cause of one of the most distinctive side effects of earlier strains of COVID-19: loss of smell.
Although this symptom has become less common as new variants spread, in 2020 a sudden loss of smell was an immediate sign to go get tested for COVID-19.
And while this loss of smell was temporary for many, for others that sense never returned properly, leaving millions of people struggling with a loss of smell for months or even years. In order to uncover the mechanisms behind this, a new study looked at olfactory epithelial samples taken from 24 people, including nine people with long-term loss of their sense of smell due to a case of COVID-19.
“One of the first symptoms commonly associated with COVID-19 infection is loss of smell,” said Bradley Goldstein, associate professor in the department of head and neck surgery and communication sciences and the department of neurobiology and lead author of the new research. , said in a press release.
“Fortunately, many people who have an impaired sense of smell during the acute phase of viral infection will regain their sense of smell within one to two weeks, but some don’t. We need to better understand why this subset of people will continue to have persistent smell loss for months or even years following being infected with SARS-CoV2.
According to a study published earlier this year, up to 5% of COVID-19 survivors have long-lasting problems with loss of smell, affecting around 15 million people. And it’s still happening, even though the rate has gone down: around 17% of people lost their sense of smell to the Omicron variant when it became dominant in 2021.
In this recent study, researchers found that among people with chronic loss of smell following COVID-19 infection, there was inflammation in the tissue of the nose where the nerve cells for smell are located, and that there were also fewer olfactory neurons in the nose. overall compared to control groups, which the researchers suspect is due to damage caused by inflammation.
In a paper published in the journal Science Translational Medicine in mid-December, researchers describe how they found no detectable SARS-CoV-2, the virus that causes COVID-19, in subjects, but inflammation continued nevertheless persisted in those with chronic odor problems.
The researchers obtained additional samples from those who had suffered from chronic loss of smell for at least four months since contracting COVID-19. None of the patients were critically ill with COVID-19 at the time of sampling, nor had they undergone medical interventions such as intubation.
A big problem was that in affected patients who previously had COVID-19, part of the immune system had been thrown out of balance – the T cells in the olfactory samples were working overtime, causing the inflammation.
The job of T cells is to attack specific foreign particles to help the body fight off a virus, but in these patients the virus is long gone.
“The results are striking,” Goldstein said. “It almost looks like some sort of autoimmune-like process in the nose.”
This is important research into a problem that has left some without the ability to smell anything, a condition called anosmia, and others with a distorted sense of smell that affects their ability to eat food without nausea. Parosmia is the term for when a person’s sense of smell is disturbed to the point that many things smell rancid or have a chemical plaster.
Previous research on the subject has largely focused on autopsies of patients who died following having COVID-19, meaning they weren’t able to ask patients regarding their smell experiences or give them tests. of smell as the researchers did in this new study.
While this research answers some questions, much more needs to be done to truly determine the reason for the long-term loss of smell in patients with COVID-19. The study notes that there are still several possibilities for the cause of the long-term damage, one being that the initial cellular damage of the acute illness may have exceeded the ability of stem cells in the olfactory area to rebuild the cells responsible. smell.
One theory seemingly disproved by this new research is that the long-term loss of smell was due to an ongoing infection, of which the researchers found no signs.
There were signs of hope – researchers observed neurons attempting to repair themselves even following long-term damage.
“We hope that modulating the abnormal immune response or repair processes in the noses of these patients might help to at least partially restore the sense of smell,” Goldstein said.
His laboratory is currently working on the study of this aspect of the question. The researchers acknowledged that their current study is limited by its smaller scope.
