Loss of taste or smell, once a hallmark COVID-19, has become a relatively rare symptom.
Less than 20% of people with COVID-19 in the UK are reporting loss of smell, new data suggests.
Among vaccinated people, Omicron may resemble a traditional cold more than prior COVID-19 variants.
Loss of taste and smell has gone from a hallmark symptom of COVID-19 to a relatively rare one.
Until recently, many people with the disease reported trouble detecting strong scents, like perfume, or tasting sweet, bitter, or spicy foods that went beyond the sense-diminishing symptoms associated with the common cold. In 2020, researchers at Massachusetts General Hospital and King's College London found that loss of taste and smell was the strongest predictor of a coronavirus infection, based on the daily symptoms of 2.6 million people.
But the Omicron variant has made traditional COVID-19 symptoms less common, while coldlike symptoms, such as a runny nose, sneezing, and a sore throat, have become more prevalent — particularly among vaccinated people.
"Loss of smell was something that many people used to report with COVID-19-symptom onset. With Omicron, that doesn't seem to be reported much at all," Dr. Andy Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health, told Insider, adding that there was "much more talk about coughs and scratchy throats with Omicron than we saw with other variant infections previously."
According to the latest data from the Zoe COVID Symptom Study, which uses a smartphone app to log how hundreds of thousands of people are feeling every day across the UK, less than 20% of people who recorded a positive test for COVID-19 in the past few weeks reported a loss of smell. The data didn't distinguish between vaccinated and unvaccinated people, but 70% of the UK population has had at least two vaccine doses.
Loss of smell now ranks 17th on Zoe's list of COVID-19 symptoms, which means it's "relatively rare," the study's principal investigator, Tim Spector, wrote Sunday on Twitter. By contrast, loss of smell was the sixth most common COVID-19 symptom among fully vaccinated people in June, when the Delta variant was dominant in the UK. In March, before Delta was detected and vaccines were widely available, 60% of UK adults ages 16 to 65 on the Zoe app reported loss of smell at some point in their illness.
Other countries have noticed a similar pattern. A December report from the Centers for Disease Control and Prevention identified just three instances of loss of taste or smell among the first 43 Omicron cases confirmed in the US.
After an outbreak at a Christmas party in Norway, just 23% of people infected with Omicron reported reduced taste, and 12% reported reduced smell, compared with 83% who reported a cough and 78% who reported a runny or stuffy nose. Most of the infected people were vaccinated with two doses of an mRNA vaccine.
Scientists are still trying to understand the link between COVID-19 and loss of taste or smell
Some people with COVID-19 may have temporary issues tasting or smelling because their nasal passages are blocked, much like what happens with a run-of-the-mill cold.
But a small 2020 study found that participants with COVID-19 lost their sense of smell even when they could breathe freely and their noses weren't runny or congested. What's more, the patients had a harder time detecting bitter or sweet tastes than patients with bad colds did.
The researchers theorized that loss of taste or smell may be related to the coronavirus interfering with the nervous system.
Another 2020 study suggested that the virus invaded cells that support olfactory neurons — the brain's messengers that help us process tastes and smells. Damage to these supporting cells could trigger swelling in the nose and inhibit a person's sense of smell, even when that person isn't congested. In severe cases, inflammation from COVID-19 could cause direct damage to olfactory neurons, leaving patients without their sense of smell for several months, years, or, perhaps, permanently.
Still, loss of taste and smell is commonly associated with mild COVID-19 symptoms. A January 2021 study found that 86% of people with mild COVID-19 cases across 18 European hospitals had a reduced sense of smell.
Scientists aren't sure why the symptom is rarer now that Omicron is spreading.
"I would not be surprised if the answer is due to differences in viral behavior in terms of where the virus best replicates," Scott Roberts, an assistant professor at Yale School of Medicine, told Insider. "With Omicron compared to Delta, we know this replicates 70 times faster in the bronchi but 10 times slower in the lung tissue."
But there's a lot left to understand about Omicron infections, Pekosz said.
"There are three things Omicron is doing — transmitting more efficiently from person to person, causing different symptoms, and showing less severe disease," he said. "We just don't know if these things are related to each other or if they are completely separate things that changed in Omicron at the same time."
At the very least, experts said, Omicron has changed the nature of a mild COVID-19 case.
"These are coldlike symptoms," Dr. Claire Steves, a scientist involved with the Zoe study, said of the latest Omicron data in a video last week. "All the classic symptoms — fever, cough, and loss of smell — are much less prevalent in the current positive cases."
Read the original article on Business Insider