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August 03, 2023

Loss of smell no longer a common sign of COVID-19 infection, researchers find

Once a hallmark of the illness, the symptom has become rare since the omicron variant arrived

Illness COVID-19
COVID Loss Smell Živa Trajbarič/Pexels

The loss of smell is far less likely with a COVID-19 infection now than it was at the start of the pandemic, according to new research from Virginia Commonwealth University Health.

At the start of the COVID-19 pandemic, the loss of smell and taste were often telltale signs that a person had been infected b the coronavirus. The unusual symptom added another layer of misery to the illness by interfering with the enjoyment of food and way people sense the world around them.

More than three years later, the risk of smell loss from a COVID-19 infection is now only 6% as likely as it was during the early months of the pandemic, a new study finds.

"Our research has shown that incidents of COVID-related smell and taste loss have dramatically changed over the course of the pandemic, to the point now that smell loss is no longer a common symptom of infection," said study leader Evan Reiter, the medical director of Virginia Commonwealth University Health's Smell and Taste Disorders Center.

Reiter and his colleagues analyzed data from more than 7 million COVID-19 patients in the U.S. to track the evolution of symptoms and how people have recovered from them over time. It's estimated that about 700,000 people lost their sense of smell as a result of a COVID-19 infection.

The reason that COVID-19 can cause the loss of smell has not been definitively answered, but some research points to the possibility that it's caused by a strong immune response that targets nerve cells at the top of the nasal cavity. When these olfactory cells become damaged, it's possible that the sensory signals sent from the nose to the brain get weakened and distorted.

The VCU Health researchers believe the loss of smell may have become less common because of increased immunity to the virus through infection and vaccination.

"This typically helps reduce the severity of future infections," Reiter said.

The study, published in the journal Otolaryngology — Head and Neck Surgery, examined patient data from April 2020 through October 2022, using the early period of the pandemic as a baseline. The researchers found that by the time the alpha and delta variants became dominant in 2021, the risk of losing smell had fallen to 74% and 64% as likely as it was when the virus was first spreading. And when omicron variants become dominant, the risk was only 6% as likely.

COVID-19 infections have been rising again in the U.S. The uptick is believe to be connected to summer travel and people congregating more indoors to stay out of the heat. People are advised to use rapid tests when they feel unwell or are planning to attend crowded indoor events, even though the pandemic is no longer front-of-mind in the way it had been over the past few years.

During the early stages of the pandemic, before there was widespread access to testing, symptoms like the loss of smell were a good indicator of infection and could be used to decide if it was necessary to quarantine. In some patients, the loss of smell was more noticeable than other common symptoms, like coughing and sore throat.

Although the loss of smell is no longer common in COVID-19 infections, it continues to have an impact on many people with long COVID. Earlier research from the VCU Health group found that two years after infection, about 7.5% of people who lost their sense of smell had not regained it and 54% had only partially recovered it. Most people who lost their sense of smell regained it within a year, according to another study published last December.

The loss of smell often has a significant impact on quality of life. It can result in an altered sense of taste, since the nose helps distinguish flavors and can ruin certain foods for people with persistent problems. About 43% of people surveyed by VCU Health in 2020 and 2021 reported feeling depressed, with many struggling to maintain a healthy diet.

For people with persistent loss of smell from COVID-19, there is ongoing research being done to better understand how to retrain the nose. Some suggest regularly sniffing essential oils to help heal damaged senses over a period of weeks or months.

"There have been a lot of different therapies out there and touted for help with this, and we've combed through all the research," said Greg Vanichkachorn, an occupational medicine specialist at the Mayo Clinic. "But the thing that we have seen to be the most effective, both in practice and in research, is something called 'olfactory retraining.' So the idea is that if we can challenge those nerves with different smells, that will help them regrow in the proper fashion."

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