About 5% of adults who get COVID-19 may develop long-lasting changes to their sense of smell or taste, based on new study findings.

Previous research already determined most of COVID’s long-lasting effects, including fatigue, shortness of breath, headache, and the so-called brain fog that causes a difficulty in thinking and concentrating.

But a new study published in The BMJ revealed that an estimated 5.6% (15 million) and 4.4% (12 million) of the 500 million COVID cases worldwide could experience long-term deficiencies in their sense of smell and taste, respectively.

Given the huge impact that loss of smell and taste can have on a person’s overall quality of life and health, the researchers warned that the new findings could contribute to the rising burden of long COVID.

On average, about 40-50% of patients with COVID-19 have reported a change in their sense of smell and taste. But little is known about the clinical course of the symptoms or how many patients develop persistent health issues after an acute infection.

To help address this knowledge gap, the researchers analyzed databases for studies of adults with COVID-19-related changes to their smell or taste. The team also looked at studies that described any factors associated with these changes and recovery time.

Studying 3,699 patients that met their criteria, the team found that smell loss persists in 5.5% of patients, while there are about 4.4% that may not recover their sense of taste. After 30 days of initial infection, 74% of patients have reported smell recovery, while 70% reported taste recovery.

The recovery rates increased as time passed, reaching a peak of 96% for smell and 98% for taste after six months. Women were also less likely to recover their sense of smell and taste than men.

Though the researchers acknowledged that their research came with several limitations, the study was well-designed and used rigorous search methods. The findings were also unaltered after further analysis.

"Our findings are likely to be of substantial relevance to general doctors and otolaryngologists in the counseling of patients with smell and taste disorders post-COVID-19," the researchers wrote, concluding that at the moment, health systems are unprepared for the scale of this challenge.