Chronic loss of smell (anosmia) following COVID-19 happens to people worldwide and is a growing problem. Though many spontaneously recover, many others live with significantly reduced quality of life from lingering loss of smell and associated loss of taste after recovering from their initial infection. To address this, a study led by researchers at Stanford University suggests that nasal injections of a person’s own plasma may help them recover their sense of smell.*

Smell loss therapies to now

Stanford Medicine otolaryngology professor Zara Patel, M.D. and colleagues surveyed people with Long COVID in 2022, and found that about 15% of those experiencing loss of smell during COVID-19 continued to have sensory loss six months later—the equivalent of about nine million Americans.

In the journal International Forum of Allergy & Rhinology, Patel and colleagues explain there are few treatments for post-COVID smell loss, and even those lack effectiveness and scientific support. Olfactory training has shown mixed results over time. Other proposed therapies with a moderate level of evidence include topical intranasal medications and oral anti-inflammatory medications.

It now appears that platelet-rich plasma (PRP), which has been used to treat mild arthritis and facial wrinkles, may also be effective for treating COVID-related chronic smell loss. PRP is composed of the liquid part of blood, and contains a high concentration of platelets and growth factors that help regrow damaged tissue. 

What the researchers did

In a randomized, double-blind, controlled trial involving 26 participants, Patel and colleagues put PRP to the test for lingering smell loss from COVID-19. Could PRP help regenerate COVID-damaged (sustentacular) cells that provide vital support to sensory cells in the nose? ”It’s a nerve damage and nerve regeneration issue that we’re dealing with,” she said. Participants:

• Had COVID-related smell loss from six (6) months to a year,
• Had already tried other therapies like olfactory training, and
• Received either three nasal injections of PRP, or a sterile saline solution (placebo) every other week for six (6) weeks.

The primary outcome sought was a change in participants’ Sniffin’ Sticks test® scores, a measure of smell threshold, discrimination (distinguishing between odors), and identification.

Smell threshold, or odor detection threshold, refers to the lowest concentration of a given odor-producing chemical compound that the human sense of smell can normally perceive.

What they found

The study results showed that patients receiving PRP injections had 12.5 times greater likelihood of improved sense of smell, and better smell discrimination, than those receiving the placebo. 

After three months from their first injection, PRP recipients:

• Gained an average of 6.25 points on their smell test versus 2.58 points for the placebo,
• Experienced their greatest gain in smell discrimination ability, and
• Showed significant improvement in smell ability (57.1% PRP v.  8.3% placebo).

There was no difference in threshold and identification improvement between groups. When self-rating smell ability, however, both groups reported similar gains. This could be due to the placebo effect or spontaneous recovery over time, the researchers explained.

What it means

Patel says post-COVID smell loss has highlighted the importance of our sense of smell. Her patients often confide that they never realized how important their sense of smell was until losing it. “People say, ‘My life has gone gray.'”

Patel already showed PRP’s safety in the nasal cavity in previous research and has now begun offering PRP injections for post-COVID smell loss outside the trial. “[T[he sooner you perform some sort of definitive intervention,” she says, “probably the better chance you have of improvement.”

*Bai, N. & Stanford University. (2023, January 13). Nasal injections could treat long-term COVID-19–related smell loss. MDLinx. https://www.mdlinx.com/news/nasal-injections-could-treat-long-term-covid-19-related-smell-loss