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.

The authors have declared no competing interest.

This work was supported by the National Institute of General Medical Sciences at the National Institutes of Health [grant GM103554 to C.S.v.B.].

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