The sudden inability to smell or taste (anosmia and ageusia) was once considered a hallmark sign of COVID-19 infection. This unique neurological symptom frequently served as an immediate clue that an illness was caused by SARS-CoV-2 rather than a common cold or the seasonal flu. The virus’s symptom profile has changed considerably as new variants have emerged. While the loss of smell or taste is still possible, it is now a far less frequent occurrence than it was during the initial waves.
Changing Prevalence of Taste and Smell Loss
The frequency of chemosensory loss (the combined loss of smell and taste) has drastically diminished since the emergence of earlier viral strains. During the initial waves of the pandemic, when the Alpha and Delta variants were dominant, approximately 50% of infected individuals reported losing their sense of smell or taste. This high rate positioned the symptom as a reliable early indicator of infection.
Data collected during the height of the Omicron variant’s spread showed a substantial reduction in this symptom. Studies found that the risk of chemosensory loss dropped by as much as 83% compared to the original strain. For instance, one analysis reported that the prevalence of anosmia was 34% during the Delta period, but it fell to 13% for the Omicron variant.
More recent research tracking evolving Omicron subvariants suggests the prevalence has fallen even further. Estimates indicate that only 3% to 4% of patients infected with current strains report the loss of smell or taste. This dramatic shift means that while the symptom remains associated with COVID-19, it is no longer the defining feature for the average case. The vast majority of people contracting the virus today retain their sense of smell and taste.
Viral Evolution and Symptom Shift
The reduction in smell and taste loss is a direct consequence of genetic changes in the virus, specifically in the spike protein. The spike protein determines which host cells the virus can infect, a concept known as viral tropism. Early SARS-CoV-2 variants were highly effective at infecting and damaging the sustentacular cells within the olfactory epithelium, the tissue responsible for detecting odors.
The latest variants, which are highly transmissible, have developed a different cellular preference due to spike protein mutations. These newer strains rely less on the host cell protease TMPRSS2 for entry, a protein found in abundance in the lower respiratory tract and the olfactory epithelium. Instead, the virus primarily utilizes the endocytic pathway, which involves cathepsin enzymes, for cell entry.
This shift in cellular mechanism means the virus is less likely to replicate in the cells that support the olfactory nerves. Current variants tend to replicate more effectively in the upper respiratory tract, such as the nasal passages and throat. This change in tropism results in more localized, cold-like symptoms and reduces the viral impact on the neurological components responsible for smell and taste perception.
The Current Typical COVID-19 Symptom Profile
Since the loss of smell and taste has become infrequent, the current typical COVID-19 symptom profile strongly resembles other common respiratory infections. The most frequently reported symptoms are milder and concentrated in the upper respiratory system. These symptoms include a sore throat, which is often one of the earliest signs of infection.
Congestion and a runny nose are also common complaints, making the infection difficult to distinguish from a common cold without testing. Many people also experience a prominent cough, which can sometimes persist, along with muscle aches and fatigue.
A fever or chills can still occur, but the overall duration of acute symptoms is often shorter than with earlier variants, lasting an average of about seven days. Less common but still reported symptoms include a headache, nausea, vomiting, or diarrhea. The overall presentation is now defined by a range of symptoms, none of which is as unique as the sudden loss of chemosensation was in the pandemic’s initial phase.
Recovery and Treatment for Anosmia
For the small percentage of individuals who still experience smell loss, recovery usually occurs spontaneously over time, though the timeline varies significantly. Most people who lose their sense of smell see it return within two to three weeks of the infection’s onset. However, for some, the condition can persist for weeks or several months.
The standard recommended non-invasive treatment for prolonged anosmia is olfactory training, often referred to as smell training. This therapy involves repeated, conscious exposure to a set of potent scents, typically twice daily for months. The training protocol usually includes four distinct odors representing different scent categories:
- Rose (flowery)
- Lemon (fruity)
- Eucalyptus (resinous)
- Clove (spicy)
The goal of this repetitive exposure is to stimulate and encourage the repair of the damaged olfactory nerve pathways. While the process requires patience, consistency is key to helping the olfactory system regenerate and regain function. A healthcare provider may also recommend a short course of nasal corticosteroid sprays to reduce inflammation in the nasal passages.