More than 5% of people who were infected with the virus that causes COVID-19 may have a long lasting loss of the senses of smell and taste, a new study finds.
Using a mathematical model and data from 18 earlier studies, an international team of researchers estimated that among those who had COVID-19, 5.6% were left with a persistent loss of smell, and 4.4% had long lasting loss of taste. The researchers also found that women were more likely than men to have persistent issues with smell and taste, according to the report published in The BMJ on Wednesday.
“We’re pretty excited about this new study,” said study coauthor Dr. Christopher von Bartheld, a neuroscientist and a professor of physiology and cell biology at the University of Nevada at Reno. “Now we know approximately how many people lose their sense of smell, and it’s a pretty huge number.”
The knowledge that so many people are affected may help spur research to find better therapies, von Bartheld said.
Five percent may not seem like a lot, but with 90.6 million COVID-19 cases in the U.S., that potentially translates into 4.5 million Americans with smell and taste issues due to the virus.
Loss of smell and taste is common among those who get COVID —historically around 40 to 50% — von Bartheld said, adding that the numbers might be different with omicron. However, most people get these senses back in a fairly short amount of time, he said.
Scientists now know how SARS-CoV-2, the virus that causes COVID-19, causes a loss of smell and taste, von Bartheld said. Fortunately, the nerve cells that carry messages to the brain about odors are not damaged, he explained. Rather, it’s mostly the support cells — the ones that help maintain the nerve cells’ health — that are infected and destroyed. These cells aren’t lost forever and in most cases they can regrow quickly, von Bartheld said.
The support cells are especially vulnerable to SARS-CoV-2 because they express lots of the kind of receptors that the virus latches onto, von Bartheld said. The nerve cells themselves do not have those receptors, which is why the virus doesn’t harm them.
What’s not yet known is why in some people the support cells don’t recover. It’s possible that lingering inflammation due to COVID may damage the lining of the nasal passages, von Bartheld said.
There is some good news, von Bartheld said. There is a therapy —olfactory training — that seems to help people get back at least some of their sense of smell. With that therapy people try to smell several common scents, such as coffee, lemon and vanilla, one at a time, several times a day over a course of weeks.
For the new research, von Bartheld and his colleagues scoured the medical literature for studies that followed people who lost their senses of taste and smell when they got COVID-19, eventually settling on 18 papers that included a total of 3,699 patients.
Using data from those studies in a mathematical model, von Bartheld and his colleagues estimated that 5.6% of people still were experiencing persistent loss of smell and taste after 180 days. Their analysis also suggested that this number was most likely an underestimate.
The new study tells us “that about 5 to 10% of people might take a long time to recover their senses of taste and smell and we don’t know if they ever will,” said Dr. Gary Desir, Paul. B. Beeson Professor of Medicine and chair of internal medicine at the Yale School of Medicine.
“COVID-19 is very new and there are a lot of things we don’t know about it,” Desir said. “A question I would ask is if people are vaccinated are they any less likely to develop changes in taste and smell. Also, does treatment of the virus make a difference.”
Desir points to a study he coauthored that is available on a preprint site but has not yet made its way through peer review to publication in a journal. In that study, researchers found that patients who had recently become infected and were given a medication to lower levels of the SARS-CoV-2 were less likely to end up with persistent loss of smell and taste.
“It would be interesting to see if giving people a drug like Paxlovid early prevents the loss of smell,” Desir said. “But researchers have to do the study to try to find that out.”