Remember back in the earliest days of Covid-19, when one of the first telltale signs of infection was loss of sense of smell? Ever wonder why this is no longer a prime issue of infection, despite there still being a very similar form of coronavirus? No? Well, millions of people do remember, and, as reported in Nature, many are studying what the cause was, why it’s no longer as much of an issue, and what can be done for those, now nearly two years after recovery, who are still suffering.
One review of over 600,000 adult patients who had recovered from Covid-19 infections found that approximately 50% of those who were infected with the primary, or alpha, variant suffered altered sense of smell. This dropped to 44% with the delta variant, and 17% with the now prevalent omicron variant. The minor alterations in the spike proteins of each variant likely explain why the earlier forms attacked nerves, but the newer ones do not.
Unfortunately, over half of those who developed altered sense of both smell and taste at the time of initial infection were still reporting disruption in these senses at one year after recovery. This is extremely distressing to millions who continue to have either complete loss, partial loss, or altered function, of these critical senses.
Initial theories of cause were based on a similar concept seen from other viruses such as the influenza virus, which have been known to either alter or knock out olfactory (nerve responsible for sense of smell) nerve fibers. In addition, the thought that swelling of the nasal tissues during acute viral infections may lead to blunting of smell sensory functions continues to come into play, although less so than initially thought. It is more likely due to the former, whereby the viral particles affect the supporting cells of olfactory neurons, blocking the ability of the nerves to perceive smells.
These changes in both the olfactory nerves as well as in the parts of the brain responsible for perceiving smells may be long term and even permanent, which has led researchers to better investigate treatment options. The inflammatory component may be treated with oral or nasal steroids, but there has been little evidence to show benefit from these. Two very small studies, with a total of under 20 patients, showed that use of platelet-rich plasma (PRP) may improve smell function over a period of three to six months.
The Clinical Olfactory Working Group, comprised of 16 smell and taste specialist researchers from around the world, issued a consensus statement recommending olfactory training to help recover sense of smell for those suffering from long term loss of smell (anosmia) due to Covid-19 infections.
The concept of smell retraining therapy is to trigger the memory of a smell, while engaging in the actual act of smelling different scents. It is recommended to use essential oils, inhalant sticks, or even fresh fruits or herbs. It’s best to use one scent from four of the major scent categories (swell, salty, savory, and resinous). Specialists recommend foregoing the foul smells such as bitter or burnt, in this process.
It is recommended to smell each scent for 10 to 20 seconds, several times per day, focusing on the goal of eventually perceiving each smell. There has been evidence that olfactory nerves can recover, and early studies have shown some benefit from this intervention.
Patients have reported anxiety and depression due to ongoing loss of smell, and there are significant risks of inability to detect something burning in the home or a gas leak. Dr. Erin O’Brien, a rhinologist (sinus specialist) from Mayo Clinic, shares some techniques on smell retraining practices here:
While the widely prevalent omicron variants carry with them multiple burdens, including higher likelihood of contagion, as well as symptoms ranging from mild to severe respiratory illness, loss of smell is much less common than it was one or two years ago. However, those who suffered from Covid-19 infections in the earliest months and year of the pandemic continue to suffer from life-altering conditions, now over two years later.