Is There Less Alteration of Smell Sensation in Patients With Omicron SARS-CoV-2 Variant Infection?

Abstract

The ongoing pandemic Coronavirus Disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a matter of global concern in terms of public health Within the symptoms secondary to SARS-CoV-2 infection, hyposmia and anosmia have emerged as characteristic symptoms during the onset of the pandemic. Although many researchers have investigated the etiopathogenesis of this phenomenon, the main cause is not clear. The appearance of the new variant of concern Omicron has meant a breakthrough in the chronology of this pandemic, presenting greater transmissibility and less severity, according to the first reports. We have been impressed by the decrease in anosmia reported with this new variant and in patients reinfected or who had received vaccination before becoming infected. Based on the literature published to date, this review proposes different hypotheses to explain this possible lesser affectation of smell. On the one hand, modifications in the SARS-CoV-2 spike protein could produce changes in cell tropism and interaction with proteins that promote virus uptake (ACE-2, TMPRSS2, and TMEM16F). These proteins can be found in the sustentacular cells and glandular cells of the olfactory epithelium. Second, due to the characteristics of the virus or previous immunity (infection or vaccination), there could be less systemic or local inflammation that would generate less cell damage in the olfactory epithelium and/or in the central nervous system.

In vitro and in vivo differences in neurovirulence between D614G, Delta And Omicron BA.1 SARS-CoV-2 variants

“…However, several studies have shown that in mice and hamsters respiratory disease is less severe after inoculation with Omicron BA.1 variant compared to earlier variants [9][10][11][12], and epidemiological data suggest that hospitalization rates are lower with the Omicron BA.1 variant compared to earlier SARS-CoV-2 variants [13,14]. Indirect evidence suggest that neurological complications in humans might be less common after infection with Omicron BA.1 compared to earlier variants such as D614G or the Delta variant, since both anosmia and Long Covid occur less frequently, although this might be-in part-related to pre-existing immunity [15][16][17][18]. A recent study in transgenic mice-in which ACE-2 expression is higher in the brain compared to the human brain [19,20] -shows frequent neuroinvasion and neurovirulence of D614G and Delta variant but not Omicron BA.1 [21].…”

Two-Year Follow-Up on Chemosensory Dysfunction and Adaptive Immune Response after Infection with SARS-CoV-2 in a Cohort of 44 Healthcare Workers

“…In general, evidence is accumulating that chemosensory dysfunction occurs less frequently in more recent variants with a prevalence of only 4–33% in Omicron [ 5 , 6 , 54 , 60 ]. This may be due to modifications in the spike protein and herewith reduced interaction with proteins of the olfactory epithelium responsible for virus uptake, such as angiotensin-converting enzyme 2 (ACE2) and transmembrane protease, serine 2 (TMPRSS2) [ 61 , 62 , 63 ].…”

Pathogenesis and progression of anosmia and dysgeusia during the COVID-19 pandemic

“…Another proposed mechanism by Rodriguez-Sevilla et al alludes to the significance of previous immunity among those infected by Omicron, postulating that re-infection in previously exposed populations would lead to a diminished systemic and local inflammatory response, causing less cellular damage in the olfactory epithelium. [ 33 ]…”