Losing one’s sense of smell and taste is perhaps one of the more bizarre symptoms of COVID-19. If it’s happened to you, you undoubtedly remember it: Waking up one morning, and suddenly discovering that your cup of coffee no longer tastes as bitter as it did before. If you were feeling up to it, you may have experimented during your isolation by dousing meals in hot sauce just to feel a faint tingle, or biting into a lemon or lime for a subtle acidity. Soon, however, the novelty would wear off, and you’d just hope your sense of smell would come back eventually.
Many respiratory infections disrupt a person’s sense of smell by creating inflammation in the nasal cavity, leading to sniffles, stuffy noses, and a hard time smelling. But SARS-CoV-2 takes its interference to a new level by entering into supporting cells in the nose and crossing the wires that connect the nose and brain.
That sounds pretty scary, and that side-effect may reveal the course of your infection and recovery. Researchers at Columbia University published a study in PLoS ONE on Wednesday that linked chemosensory disruption—the loss of smell or taste following a COVID infection—to a person’s immune reaction to the virus, the remnants of which can linger for months in their bloodstream. To do this, they measured the levels of antibodies of 306 people who donated convalescent plasma in the spring of 2020 following a self-reported COVID-19 infection.
They found that people who lost their sense of smell or taste were each about twice as likely as those who didn’t lose those senses to have high levels of IgG antibodies. These antibodies signify an immune response, and have also been shown to rise once a person has recovered from a COVID-19 infection, as well as following vaccination. Having higher levels of IgG antibodies isn’t necessarily better or worse than having lower levels, but the researchers noted that high antibody levels are characteristic of a severe bout of COVID-19.
We don’t know if this association would hold today—the patients sampled all reported a COVID-19 infection in early 2020, and new research has found that the rates of smell and taste loss are lower with newer COVID variants. The study participants were not followed over time, so there’s no way to know how these high antibody levels affected them, either in the persistence of their symptoms or upon re-exposure to the virus. Some people who lose their sense of smell or taste following a COVID-19 infection take months or longer to regain it; further research is needed to drill down to why this happens, and determine ways to return these senses to patients.
Still, the new findings add another wrinkle into our ongoing attempts to understand what COVID infection means in the long run—especially as we see reinfection rates rising higher and higher.