Nearly half of those who fell ill with Covid in the first wave of infection may have long-lasting and even permanent changes in their sense of smell, according to preliminary research from Sweden.

A sudden loss of odor, or a worsened or distorted perception of odors, appeared as an unusual symptom of Covid early in the pandemic. While many people recovered quickly, others found that their sense of smell never really returned to normal.

To find out how common the disabilities can be, researchers at Karolinska Institutet in Stockholm conducted extensive tests on 100 individuals affected by Covid in the first wave of infections that swept through Sweden in the spring of 2020.

Their early findings show that 18 months after recovering from Covid, very few people – only 4% – had completely lost their sense of smell, but a third had a reduced ability to detect odors and almost half complained of parosmia, where the feeling of smell is distorted. Most of those with impaired sense of smell were unaware of this before joining the study.

The researchers 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 one-fifth were found to have similar deficiencies in their sense of smell, suggesting that odor disorders were common in the general population before Covid struck.

To write in one oppression which has not yet been reviewed, the researchers conclude that 65% of those who recovered from Covid showed either an odor loss, a decreased sense of smell or distortions of the mind 18 months after infection, compared to 20% of those who had not caught the virus. “Given how long it has been since then [the] the first insult to the olfactory system, it is likely that these odor problems are permanent, ”they wrote.

The volunteers recruited for the study were healthcare professionals who were regularly tested for Covid from the beginning of the epidemic in Sweden. Because the study focused on people who caught Covid in the first wave, none of the volunteers had been vaccinated at that time. For the same reason, their infections were caused by older versions of the virus, not the Omicron variant, which is now spreading rapidly around the world.

Analyzes from the UK Health Security Agency indicate that there is a loss of smell or taste less than half as common with Omicron than the Delta variant, but Dr Johan Lundström, who led the research at Karolinska Institutet, said that there was no reliable data showing that Omicron was less dangerous for the odor system.

A slight loss of smell, or noticing that certain smells smell strange, may not change the lives of many, but Lundström said that a strong loss of smell can lead to depression and that people change their diet, often for the worse, which makes them weight.

“When you can not smell, all you can feel are the five basic taste properties, tactile sensations and spices,” he said. “Unconsciously, people start adding more sugar and fat, or have an increased craving for fried foods for consistency, all to get some pleasure from eating.”

Lundström said that the biggest surprise with the study was that almost 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 be helped by training odor,” he added. “They may not regain 100% of their previous performance, but most of them will, with training, return to a point where their impaired sense of smell will not affect their lives.”