In-Depth: Why omicron alters smell less frequently

COVID-19 omicron
Posted at 5:12 PM, Feb 22, 2022
and last updated 2022-02-22 20:36:20-05

SAN DIEGO (KGTV) – Loss of taste or smell were hallmarks of COVID infection throughout most of the pandemic, but new studies reveal the symptoms are much less prevalent with omicron.

This week, Italian researchers released a study on nearly 800 patients with mild-to-moderate COVID. They found that 33 percent of people infected with omicron experienced taste or smell issues compared to 67 percent infected during the first wave in 2020. The study has not yet undergone peer review for an academic journal.

In January, health officials in the United Kingdom released data suggesting these symptoms were even rarer: 13 percent of people infected with omicron experienced loss of smell or taste compared to 34 percent of delta cases.

The UK ZOE study estimates about one in five people report smell or taste loss with omicron.

There are at least three ways that SARS-CoV-2 can cause changes in smell, but one of the leading theories is that the virus can infect the olfactory nerve that conveys smells from the nose to the brain.

“Earlier variants of SARS-CoV-2 attack that very nerve, and omicron just doesn’t do as good a job at getting at that nerve,” said UC San Diego infectious disease expert Dr. Robert Schooley.

Scientists have learned that omicron and delta use different molecular pathways to invade cells, making certain parts of the body more susceptible to one variant over the other.

“The olfactory nerve has a slightly different makeup of receptors that favors the delta variant over the omicron variant,” said Dr. Schooley. “So the omicron variant doesn’t destroy that nerve as effectively as the delta variant does.”

Delta specializes in attaching to cells with a molecule called TMPRSS2, which is plentiful in cells in the olfactory nerve. This molecule acts like a pair of scissors, and delta’s spike protein is easy to cut. Once sliced in half, delta’s spike can easily slide inside the cell and hijack it.

By contrast, omicron’s spike is difficult to cut.

“If you can’t cut it up, it becomes very clunky and clumsy and is much less likely to infect that particular olfactory cell,” said UC San Francisco’s Dr. Peter Chin-Hong.

This pattern plays out in other regions of the body, Chin-Hong noted. Omicron specializes in attacking cells without TMPRSS2, such as those in the upper respiratory tract.

Cells deep inside the lungs have high levels of TMPRSS2, and that’s where delta does its worst damage.