Prevalence of Olfactory Dysfunction with the Omicron Variant of SARS-CoV-2: A Systematic Review and Meta-analysis

Abstract

The omicron variant is thought to cause less olfactory dysfunction than previous variants of SARS-CoV-2, but the reported prevalence differs greatly between populations and studies. Our systematic review and meta-analysis provide information about regional differences in prevalence as well as an estimate of the global prevalence of olfactory dysfunction based on 41 studies reporting on nearly 600,000 patients infected with the omicron variant. Our estimate of the omicron-induced prevalence of olfactory dysfunction in populations of European ancestry is 11.6%, while it is significantly lower in all other populations, at 2.9-5.4%. When ethnic differences and population sizes are taken into account, the global prevalence of omicron-induced hyposmia in adults is estimated at 5.2%. Omicron's effect on olfaction is 3-4fold lower than that of the alpha or delta variant, according to previous meta-analyses and our analysis of studies that directly compared prevalence of olfactory dysfunction between omicron and previous variants. The profile of prevalence differences between ethnicities mirrors the results of a recent genome-wide association study that implicated a gene locus encoding an odorant-metabolizing enzyme, UDP glycosyltransferase, to be linked to the extent of COVID-related loss of smell. Our analysis is consistent with the hypothesis that this enzyme contributes to the observed population differences.

Detection of anti-nucleocapsid antibodies associated with primary SARS-CoV-2 infection in unvaccinated and vaccinated blood donors

“…As a result, a large majority of survey-reported SCIs in the validation set were associated with COVID-19 symptoms (92%). In contrast, a meta-analysis of Omicron infections estimated 32.4% of infections were asymptomatic (31). This may result in a slight upward bias in overall sensitivity estimates.…”

Assessment of clinical characteristics and viral load in individuals infected by Delta and Omicron variants of SARS-CoV-2

“…The lower prevalence of olfactory and taste disorders among Omicron-infected individuals when compared to other previous variants has been reported previously [ [28] , [29] , [30] , [31] , [32] , [33] ]. A recent meta-analysis including 62 studies and 626,035 patients reported that olfactory disturbances caused by Omicron are about 2–10 times less common than observed with the Alpha or Delta variants [ 34 ]. Features associated with the mechanism of Omicron entry into the host cell may explain, at least in part, a lower efficiency in infecting olfactory epithelial cells [ 28 ].…”

Position paper on olfactory dysfunction: 2023

“…Similar results were demonstrated by the REal-time Assessment of Community Transmission (REACT-1) study, which reported subjective symptoms from 1,542,510 randomly selected participants in England from 1.5.20 to 31.3.22 (121) . A recent systematic review and meta-analysis of OD in patients infected with the omicron variant demonstrated a global prevalence of 3.7% (122) . However, this varied geographically, with higher rates seen in people of European ancestry (11.7%).…”