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.

Keywords: COVID-19; Omicron variant; anosmia; inflammation; vaccines.

Figure 1

Schematic mechanism proposal of anosmia/hyposmia in COVID-19. (A) SARS-CoV-2 alpha variant. (1) Infection and destruction of olfactory epithelial supporting cells (olfactory sustentacular cells), resulting in inflammation, and abnormalities in local homeostasis; (2) infection or immune-mediated damage of surrounding cells (vascular cells) resulting in hypoperfusion, inflammatory cell recruitment, cytokine release, and the production of chemical neurotoxins. (B) SARS-CoV-2 Omicron variant. Omicron mechanism of cell entry based on a TMPRS22 dependent and non-dependent manner may involve a more heterogenous tropism with less replication and the consequent minor local inflammation produced. (C) SARS-CoV-2 vaccines may not alter the levels of replicating virus in the olfactory epithelium once viral infection establishes but may instead protect through accelerated clearance or enhanced neutralization of infectious viral particles.