Millions of Patients Still Lack Smell, Taste After Recovering from COVID-19

Up to 5% of adults may have long-lasting distorted smell and taste after recovering from COVID-19, according to research published in the BMJ, which can cause distress and future neurological issues.^1,2 Researchers also found that these symptoms manifested in womResearchers also found that these symptoms manifested in womene more than men.¹

More than 550 million individuals contracted COVID-19 since July 2022.1 With 50% of patients reporting smell or taste dysfunction, 15 million people (5.6%) and 12 million (4.4%) could face permanent smell or taste issues, respectively.¹ This can result in certain smells or tastes being “disgusting and emotionally distressing” for patients with long COVID-19.²

“This is a strong and important study, alerting us once again to the difficulties inherent in charting the scale of long-term damage caused by COVID-19,” said Danny Altmann, PhD, a professor of immunology at Imperial College London, who was not involved with the research, to The Guardian. “The authors conducted a rather rigorous meta-analysis across several cohorts, modelling the time to recovery of taste and smell. It goes without saying that problems with taste and smell are non-trivial for quality of life.”²

Taste and smell dysfunction, also known as chemosensory dysfunction, occurs when receptors that send signals of tastes and odors to the brain are blocked.¹ These sensorineural mechanisms are thought to facilitate the specific manifestation of COVID-19 symptoms.¹ They were some of the most early and prominent symptoms of COVID-19.¹

The experts performed a meta-analysis of 3699 patients across 18 studies, using statistical cure models and time-to-event data to estimate the recovery of patients with chemosensory dysfunction post-COVID-19.¹

Individual patient data (IPD) at 30, 60, 90, and 180 days show that 96% of patients reported smell recovery after 6 months, whereas 98% of patients self-reported taste recovery.¹ This aligned with scientists’ predictions that patients were most likely to recover smell within 3 months of COVID-19.¹

Further data at the 6-month mark revealed that many patients may not fully recover from chemosensory dysfunction, with some findings showing that at least 7% to 8% of patients dealt with a year of impaired smell and taste.¹ These results were comparable to the researchers’ prediction.¹

Some underlying factors including heavy nasal congestion and severe chemosensory dysfunction at the onset of infection, which resulted in patients less likely to recover their sense of smell.¹ Women were also more likely to face these permanent consequences.¹

Smell dysfunction was found to potentially predict depression and other neurodegenerative disorders, as well.¹ Dysfunctional taste and smell were also associated with malnutrition, cognitive decline, and accelerated neurodegenerative disease.¹

Recovery could look different depending on the variant.¹ Only 16% of people with the omicron variant experienced chemosensory dysfunction, compared to 44% who had these symptoms during the spread of the delta variant.¹

Although recovery seems unlikely for these individuals, past studies prove that it is not impossible.¹ Personalized treatment and follow-up are necessary, and relevant future research should be done on the stratified recovery with different variants, according to the researchers.¹

References

1. Tan B, Han R, Zhao J, Tan N, et al. Prognosis and persistence of smell and taste dysfunction in patients with covid-19: meta-analysis with parametric cure modelling of recovery curves. The BMJ. June 14, 2022. Accessed August 8, 2022. doi:10.1136/bmj-2021-069503. https://www.bmj.com/content/378/bmj-2021-069503
2. Gregory, A. Covid study finds millions have long-term smell or taste problems. The Guardians. July 27, 2022. Accessed August 5, 2022. https://www.theguardian.com/world/2022/jul/27/covid-study-finds-millions-have-long-term-smell-or-taste-problems