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

Hearing and vision may not be considered hierarchically superior senses anymore, as a new study sheds light on the importance of taste and smell for quality of life.

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