Half of first-wave Covid cases may have lasting harm to sense of smell

According to preliminary research from Sweden, nearly half of those who became ill with Covid in the first wave may have long-term and even permanent changes to their sense of smell.

Early on in the Pandemic, a sudden loss of smell, or an impaired or distorted perception of odours, emerged as an unusual symptom. Many people recovered quickly, but others found that their sense of smell never returned to normal.

To find out how common the impairments might be, scientists at the Karolinska Institute ran comprehensive tests on 100 individuals who caught Covid in the first wave of infections that swept through Sweden in spring 2020.

Only 4% of people had lost their sense of smell completely after recovering from Covid, but a third had a reduced ability to detect odors, and nearly half complained of parosmia, where the sense of smell is distorted. Most of the people with a reduced sense of smell were unaware of it before they joined the study.

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The scientists ran the same tests on a group of people who had tested negative for Covid and found that they had avoided the virus. It was found that about a fifth of them had the same deficiency in their sense of smell, suggesting that smell disorders were common in the general population before Covid struck.

In a preprint that has not yet been peer reviewed, the scientists conclude that 70% of those who recovered from Covid showed a loss of smell, a reduced sense of smell, or distortions to the sense 18 months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 disease It is likely that the olfactory problems are permanent because of the amount of time since the initial insult.

The volunteers for the study were healthcare workers who were regularly tested for Covid. The study focused on people who caught Covid in the first wave, so none of the volunteers had beenvaccinated at the time. Older versions of the virus caused their infections, not the Omicron variant that is spreading rapidly around the world.

According to the analysis by the UK Health Security Agency, a loss of smell or taste is less common with Omicron than the Delta variant, but Dr. Lundstrm said there was no reliable data showing that Omicron was less.

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

He said that when you can't smell, all you can sense is the five taste qualities. People start to add more sugar and fat, or have an increased urge for fried food, all to get some enjoyment out of eating.

Almost half of people who had recovered from Covid reported a distorted sense of smell, which was the greatest surprise of the study. Many of these people can get help by doing olfactory training. Most of them will get back to a point where their reduced sense of smell won't affect their lives if they train hard.