Monday, 26 February, 2024
HomeCoronavirus WatchLong-term damaged sense of smell in 50% of 1st wave COVID cases...

Long-term damaged sense of smell in 50% of 1st wave COVID cases – Karolinska study

Nearly half of those who became ill with COVID-19 in the first wave of infections may have long-term and even permanent changes to their sense of smell, according to preliminary research from Sweden.

A sudden loss of smell, or an impaired or distorted perception of odours, emerged as an unusual symptom of COVID early in the pandemic. While many people recovered quickly, others found their sense of smell never quite returned to normal.

To find out how common the impairments might be, scientists at the Karolinska Institute in Stockholm ran comprehensive tests on 100 people who caught COVID in the first wave that swept through Sweden in 2020.

Their early findings show that 18 months after recovering from COVID, very few people – only 4% – had lost their sense of smell entirely, but a third had a reduced ability to detect odours, and nearly half complained of parosmia, where the sense of smell is distorted. Most of those with a reduced sense of smell were unaware of it before joining the study, reports The Guardian.

The scientists then ran the same tests on a control group of people who tested negative for COVID antibodies, indicating that they had managed to avoid the virus. About a fifth were found to have similar deficiencies in their sense of smell, implying that smell disorders were common in the general population before COVID struck.

Writing in a preprint on medRxiv that has not yet been peer reviewed, the scientists conclude that 65% of those who recovered from COVID displayed either a loss of smell, a reduced sense of smell, or distortions to the sense 18 months after the infection, compared with 20% of those who had not caught the virus. “Given the amount of time since [the] initial insult to the olfactory system, it’s possible these olfactory problems are permanent,” they wrote.

The volunteers recruited for the study were healthcare workers who were regularly tested for COVID from the start of the epidemic in Sweden. Because the study focused on people who were infected in the first wave, none of the volunteers had been vaccinated at the time. For the same reason, their infections were caused by older versions of the virus, not the latest Omicron variant.

Analysis by the UK Health Security Agency suggests a loss of smell or taste is less than half as common with Omicron than the Delta variant, but Dr Johan Lundström, who led the research at the Karolinska Institute, said there were no reliable data proving Omicron was less dangerous to the olfactory system.

A minor loss of smell, or noticing that certain odours smell weird, may not be life changing for many, but Lundström said a severe loss of smell could lead to depression and to people changing their diets, often for the worse, causing them to put on weight.

“When you cannot smell, all you can sense is the five basic taste qualities, tactile sensations and spices,” he said. “Unconsciously, people start to add more sugar and fat, or have an increased urge for fried food for the texture, all to get some enjoyment out of eating.”

Lundström said the greatest surprise of the study was that nearly half of the people who had recovered from COVID reported a distorted sense of smell so long after the infection. “Many of these individuals can get help by doing olfactory training,” he added. “They might not regain 100% of past performance, but most of them will, with training, get back to a point where their reduced sense of smell will not affect their lives.”

Study details

High prevalence of olfactory disorders 18 months after contracting COVID-19

Arnaud Tognetti, Evelina Thunell, Mats J Olsson, Nina Greilert Norin, Sebastian Havervall, Charlotte Thalin, Johan N Lundstrom.

Reduced olfactory function is the symptom with the highest prevalence in COVID-19 with nearly 70% of individuals with COVID-19 experiencing partial or total loss of their sense of smell at some point during the disease.

Recent reports suggest that more than 7 months after recovering from COVID-19, a large proportion of these individuals still have olfactory dysfunction of some form.
To establish the prevalence of olfactory dysfunction 18 months and beyond, we tested 100 individuals with established COVID-19 in the first wave of the pandemic using psychophysical full-scale testing of smell and taste functions as well as assessments of parosmia. Participants were recruited from an ongoing study, comprising healthcare workers at a hospital in Stockholm, Sweden, that are regularly tested for SARS-CoV-2 IgG antibodies since the start of the pandemic in Sweden.

To assess potential skewed recruitment of individuals with prior olfactory dysfunction and assess normal rate of dysfunctions in the used population, 44 SARS-CoV-2 IgG naive individuals were also tested as a control group. One and a half year after COVID-19, more than one third of individuals recovered from COVID-19 demonstrated a clinical reduction in their sense of smell. Critically, nearly half of COVID-19-recovered individuals complaint about parosmia. Prevalence of gustatory dysfunction was, however, low (3%). In summary, a full 65% of individuals recovered from COVID-19 experience olfactory dysfunction of some form 18 months later. Given the amount of time since initial insult to the olfactory system, it is likely that these olfactory problems are permanent.


The Guardian – Half of first-wave Covid cases may have lasting harm to sense of smell (Open access)


medRxiv article – High prevalence of olfactory disorders 18 months after contracting COVID-19 (Open access)


See more from MedicalBrief archives:


Association between loss of smell in after SARS-CoV-2 infection and cognitive impairment


French wine tasters ask for vaccine priority to protect sense of smell and taste


Long COVID less common than previously estimated — UK National Statistics


Long COVID-19 may have affected 2m in England – REACT-2


Many post-COVID patients get new medical problems, US study finds



MedicalBrief — our free weekly e-newsletter

We'd appreciate as much information as possible, however only an email address is required.