Comparison of clinical characteristics between SARS-CoV-2 Omicron variant and Delta variant infections in China

Associations between clinical data, vaccination status, antibody responses, and post-COVID-19 symptoms in Thais infected with SARS-CoV-2 Delta and Omicron variants: a 1-year follow-up study

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), led to a global pandemic from 2020. In Thailand, five waves of outbreaks were recorded, with the fourth and fifth waves driven by the Delta and Omicron variants, resulting in over 20,000 new confirmed cases daily at their peaks.

METHODS

This cross-sectional study investigated the associations between clinical symptoms, vaccination status, antibody responses, and post-COVID-19 sequelae in COVID-19 patients. Plasma samples and clinical data were collected from participants admitted to hospitals in Thailand between July 2021 and August 2022, with follow-ups conducted for one year. The study included 110 participants infected with either the Delta (n = 46) or Omicron (n = 64) variants. Virus genotypes were confirmed by RT-PCR of nasal swab RNA and partial nucleotide sequencing of the S gene. IgG and IgA antibody levels against the receptor-binding domain (RBD) of SARS-CoV-2 Delta and Omicron variants were measured in plasma samples using ELISA.

RESULTS

Pneumonia was found to be associated with Delta variant infections, while sore throat, congestion or runny nose, and headache were linked to Omicron infections. Vaccination with fewer than two doses and diabetes mellitus were significantly associated with higher disease severity. Specific IgG and IgA antibodies against the RBD of the Delta variant generally rose by day 14 and were maintained for up to two months, whereas the pattern of antibody response to the Omicron variant was less clear. Antibody risings were found to be positively associated with pneumonia, certain underlying conditions (obesity, hypertension, dyslipidemia, and diabetes mellitus), and age ≥ 60 years. Delta variant infections were associated with forgetfulness, hair loss, and headache during the 1-year post-infection period. Females were more likely to experience hair loss, forgetfulness, and joint pain, while older age was associated with joint pain.

CONCLUSIONS

This study enhances our understanding of SARS-CoV-2 infections in Thais, particularly concerning the Delta and Omicron variants. The findings can inform public health planning and response strategies for future outbreaks of SARS-CoV-2 or other emerging viral diseases.

Clinical characteristics and severity markers in hospitalized COVID-19 patients from western Mexico: a comparative analysis of Delta and Omicron variants

Introduction

COVID-19 is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a virus notable for its rapid mutation rate, which has led to the emergence of various variants such as Delta and Omicron, each with potentially different levels of transmissibility and virulence. Therefore, this study aims to compare clinical charactheristics and markers associated with the severity of COVID-19 in hospitalized patients from western Mexico who were infected with the Delta and Omicron variants of SARS-CoV-2.

Methods

This cross-sectional study involved 66 patients hospitalized for COVID-19, diagnosed by RT-qPCR. SARS-CoV-2 variants were identified through whole genome sequencing using the COVIDseq platform from Illumina. Upon admission, patients underwent a clinical history assessment, blood gas analysis, and blood biometry. Additionally, several tests and markers were measured, including the percentage of neutralizing antibodies, erythrocyte sedimentation rate (ESR), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNFα), D-dimer, lactate dehydrogenase (LDH), C-reactive protein (CRP), and ferritin.

Results and discussion

Patients hospitalized with the Omicron were found to be older, compared to those infected with the Delta (64 vs. 54 years, p = 0.006). Additionally, a higher proportion of male patients were observed in the Omicron compared to the Delta (p = 0.029). Both Omicron and Delta variants were associated with lymphopenia, although the lymphocyte count was lower in Omicron (0.9 vs. 0.56 10x3/L; p = 0.007). The COVID-GRAM scale indicated a high risk for severe disease in both groups, but the score was higher in Omicron compared to Delta (157 vs. 128 points; p = 0.0004). Patients infected with Omicron exhibited a lower percentage of neutralizing antibodies than those with Delta (35.99 vs. 81%; p < 0.05), regardless of their vaccination status. Among the markers assessed, globular ESR was found to be lower in Omicron compared to Delta (30.5 vs. 41.5 mm/h; p = 0.001), while ferritin levels were higher in patients infected with the Omicron (1,359 vs. 960.6 μg/L; p = 0.007). In patients with severe COVID-19, markers such as lymphopenia, neutralizing antibody levels, ferritin, and COVID-GRAM scores are elevated in the Omicron variant, while only the leukocyte count and ESR for the Delta variant.

Differential immunometabolic responses to Delta and Omicron SARS-CoV-2 variants in golden syrian hamsters

Delta (B.1.617.2) and Omicron (B.1.1.529) variants of SARS-CoV-2 represents unique clinical characteristics. However, their role in altering immunometabolic regulations during acute infection remains convoluted. Here, we evaluated the differential immunopathogenesis of Delta vs. Omicron variants in Golden Syrian hamsters (GSH). The Delta variant resulted in higher virus titers in throat swabs and the lungs and exhibited higher lung damage with immune cell infiltration than the Omicron variant. The gene expression levels of immune mediators and metabolic enzymes, Arg-1 and IDO1 in the Delta-infected lungs were significantly higher compared to Omicron. Further, Delta/Omicron infection perturbed carbohydrates, amino acids, nucleotides, and TCA cycle metabolites and was differentially regulated compared to uninfected lungs. Collectively, our data provide a novel insight into immunometabolic/pathogenic outcomes for Delta vs. Omicron infection in the GSH displaying concordance with COVID-19 patients associated with inflammation and tissue injury during acute infection that offered possible new targets to develop potential therapeutics.

Comparison of the Measurement Properties of EQ-5D-5L and SF-6Dv2 in COVID-19 Patients in China

BACKGROUND AND OBJECTIVES

There are limited studies comparing the health utility values of EQ-5D-5L and SF-6Dv2 within the same patient cohorts. The widespread transmission and recurring infections associated with Omicron variants amid the COVID-19 pandemic have resulted in substantial health detriments and increased utilisation of health care resources. This highlights the crucial need to assess the loss in quality-adjusted life years (QALYs). Therefore, this study aims to compare the ceiling and floor effects, agreement, correlation and responsiveness between EQ-5D-5L and SF-6Dv2 based on COVID-19 patients during the Omicron outbreak in China.

METHODS

We recruited 694 COVID-19 patients across mainland China to participant in an online questionnaire survey from January to February 2023. The questionnaire encompassed queries concerning the sociodemographic and health details of the participants, who were requested to recollect their health status during and after experiencing COVID-19 using the EQ-5D-5L and SF-6Dv2 questionnaires. Epanechnikov kernel density plots were used to visualise the ceiling and floor effects for both instruments. Agreement was assessed by Bland-Altman graph and intraclass correlation coefficient (ICC). Correlation was evaluated using linear regression, Pearson's correlation and Spearman's correlation. The standardised response mean (SRM) and relative efficiency (RE) were used to examine the responsiveness of EQ-5D-5L and SF-6Dv2 at detecting the health improvement after COVID-19 infection and the difference in dichotomous health indicators.

RESULTS

In total, 648 valid responses from patients aged 35.6 ± 15.0 years were involved in analysis. The EQ-5D-5L utility indices were 0.58 ± 0.33 and 0.92 ± 0.14 during and after COVID-19 infection, respectively, which were significantly higher than indices of the SF-6Dv2 utility (0.43 ± 0.31 and 0.81 ± 0.19, p < 0.001). A ceiling effect of EQ-5D-5L larger than that of SF-6Dv2 was observed during COVID-19 infection (49.5% vs 21.6%). Intraclass correlation coefficients between EQ-5D-5L and SF-6Dv2 during and after COVID-19 infection were 0.69 and 0.55, respectively. The utility indices of EQ-5D-5L and SF-6Dv2 were highly correlated, with Pearson's correlation coefficients of 0.76 and 0.70 (p < 0.001) during and after COVID-19 infection, respectively. The spearman's correlations were moderate to high between dimensions of EQ-5D-5L and SF-6Dv2 (p < 0.01). Both EQ-5D-5L and SF-6Dv2 were responsive to detect health improvement after COVID-19 and the differences in dichotomous health indicators.

CONCLUSIONS

The utility indices generated by EQ-5D-5L and SF-6Dv2 in COVID-19 patients demonstrate strong correlation and responsiveness. However, the agreement between these two instruments does not reach a satisfactory level. Consequently, these two measures cannot be used interchangeably. In situations where apprehensions about ceiling effects affecting outcome measurement arise, it is advisable to consider SF-6Dv2 as a preferable outcome measure for studies on patients with COVID-19.

Clinical characteristics and outcomes of maintenance hemodialysis patients with COVID-19 during the Omicron wave of the pandemic in Beijing: a single center retrospective study

BACKGROUND

The clinical manifestations and prognosis of hemodialysis patients with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) during the Omicron wave of the pandemic infection were still unclear. This study investigated the clinical characteristics of patients undergoing maintenance hemodialysis (MHD) infected with it.

METHODS

This retrospective single-center study included 151 patients undergoing MHD. Healthcare workers were selected as control group were assessed from December 1, 2022 to March 31, 2023. Clinical data, laboratory test results, treatment protocols, and prognoses were collected and analyzed.

RESULTS

The study population included 146 patients with MHD, 93 (63.7%) of whom were infected with SARS-CoV-2. The number of non-severe, severe, and critical cases was 84 (90.3%), 4 (4.3%), and 5 (5.3%), respectively. Six patients (6.5%) died during the study period. The main symptoms of SARS-CoV-2 infection, including fever, cough, and fatigue, were less common in patients with MHD than the controls. During SARS-CoV-2 infection, the C-reactive protein (2.9 vs. 11.8 mg/dl, p < 0.0001) and ferritin levels(257.7 vs. 537 ng/l, p < 0.0001) were elevated. The hemoglobin(113vs 111 g/L, p = 0.0001) and albumin levels(39.4 vs. 36.1 g/L, p < 0.0001) decreased. Generally, it took two months for the hemoglobin levels to recover. Positivity rate for SARS-COV-2 serum immunoglobin G (IgG) antibodies and IgG titers were lower in dialysis patients than the controls. Age was positively associated with disease severity, while age and hyponatremia were associated with death.

CONCLUSIONS

Patients with MHD and COVID-19 were primarily classified as non-severe. SARS-CoV-2 infection would soon lead to the increase of inflammation related acute response protein in dialysis patients, and then lead to the decrease of hemoglobin and albumin. About 9.6% in HD patients were severe cases and had poor prognosis. Advanced age and hyponatremia were associated with disease severity and prognosis.

Molecular characterization of SARS-CoV-2 Omicron clade and clinical presentation in children

Since its emergence, SARS-CoV-2 Omicron clade has shown a marked degree of variability and different clinical presentation compared with previous clades. Here we demonstrate that at least four Omicron lineages circulated in children since December 2021, and studied until November 2022: BA.1 (33.6%), BA.2 (40.6%), BA.5 (23.7%) and BQ.1 (2.1%). At least 70% of infections concerned children under 1 year, most of them being infected with BA.2 lineages (n = 201, 75.6%). Looking at SARS-CoV-2 genetic variability, 69 SNPs were found to be significantly associated in pairs, (phi <  - 0.3 or > 0.3 and p-value < 0.001). 16 SNPs were involved in 4 distinct clusters (bootstrap > 0.75). One of these clusters (A23040G, A27259C, T23617G, T23620G) was also positively associated with moderate/severe COVID-19 presentation (AOR [95% CI] 2.49 [1.26-4.89] p-value: 0.008) together with comorbidities (AOR [95% CI] 2.67 [1.36-5.24] p-value: 0.004). Overall, these results highlight the extensive SARS-CoV-2 Omicron circulation in children, mostly aged < 1 year, and provide insights on viral diversification even considering low-abundant SNPs, finally suggesting the potential contribution of viral diversification in affecting disease severity.

Effects of Recombinant SARS-CoV-2 Spike Protein Variants on Platelet Morphology and Activation

Platelets are central elements of hemostasis and also play a pivotal role in the pathogenesis of thrombosis in coronavirus disease 2019. This study was planned to investigate the effects of different severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) recombinant spike protein variants on platelet morphology and activation. Citrated whole blood collected from ostensibly healthy subjects was challenged with saline (control sample) and with 2 and 20 ng/mL final concentration of SARS-CoV-2 recombinant spike protein of Ancestral, Alpha, Delta, and Omicron variants. Platelet count was found to be decreased with all SARS-CoV-2 recombinant spike protein variants and concentrations tested, achieving the lowest values with 20 ng/mL Delta recombinant spike protein. The mean platelet volume increased in all samples irrespective of SARS-CoV-2 recombinant spike protein variants and concentrations tested, but especially using Delta and Alpha recombinant spike proteins. The values of both platelet function analyzer-200 collagen-adenosine diphosphate and collagen-epinephrine increased in all samples irrespective of SARS-CoV-2 recombinant spike protein variants and concentrations tested, and thus reflecting platelet exhaustion, and displaying again higher increases with Delta and Alpha recombinant spike proteins. Most samples where SARS-CoV-2 recombinant spike proteins were added were flagged as containing platelet clumps. Morphological analysis revealed the presence of a considerable number of activated platelets, platelet clumps, platelet-monocyte, and platelet-neutrophils aggregates, especially in samples spiked with Alpha and Delta recombinant spike proteins at 20 ng/mL. These results provide support to the evidence that SARS-CoV-2 is capable of activating platelets through its spike protein, though such effect varies depending on different spike protein variants.

It's in the blood: a review of the hematological system in SARS-CoV-2-associated COVID-19

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to an unprecedented global healthcare crisis. While SARS-CoV-2-associated COVID-19 affects primarily the respiratory system, patients with COVID-19 frequently develop extrapulmonary manifestations. Notably, changes in the hematological system, including lymphocytopenia, neutrophilia and significant abnormalities of hemostatic markers, were observed early in the pandemic. Hematological manifestations have since been recognized as important parameters in the pathophysiology of SARS-CoV-2 and in the management of patients with COVID-19. In this narrative review, we summarize the state-of-the-art regarding the hematological and hemostatic abnormalities observed in patients with SARS-CoV-2-associated COVID-19, as well as the current understanding of the hematological system in the pathophysiology of acute and chronic SARS-CoV-2-associated COVID-19.

Development of a model by LASSO to predict hospital length of stay (LOS) in patients with the SARS-Cov-2 omicron variant

The length of stay (LOS) in hospital varied considerably in different patients with COVID-19 caused by SARS-CoV-2 Omicron variant. The study aimed to explore the clinical characteristics of Omicron patients, identify prognostic factors, and develop a prognostic model to predict the LOS of Omicron patients. This was a single center retrospective study in a secondary medical institution in China. A total of 384 Omicron patients in China were enrolled. According to the analyzed data, we employed LASSO to select the primitive predictors. The predictive model was constructed by fitting a linear regression model using the predictors selected by LASSO. Bootstrap validation was used to test performance and eventually we obtained the actual model. Among these patients, 222 (57.8%) were female, the median age of patients was 18 years and 349 (90.9%) completed two doses of vaccination. Patients on admission diagnosed as mild were 363 (94.5%). Five variables were selected by LASSO and a linear model, and those with P < 0.05 were integrated into the analysis. It shows that if Omicron patients receive immunotherapy or heparin, the LOS increases by 36% or 16.1%. If Omicron patients developed rhinorrhea or occur familial cluster, the LOS increased by 10.4% or 12.3%, respectively. Moreover, if Omicron patients' APTT increased by one unit, the LOS increased by 0.38%. Five variables were identified, including immunotherapy, heparin, familial cluster, rhinorrhea, and APTT. A simple model was developed and evaluated to predict the LOS of Omicron patients. The formula is as follows: Predictive LOS = exp(1*2.66263 + 0.30778*Immunotherapy + 0.1158*Familiar cluster + 0.1496*Heparin + 0.0989*Rhinorrhea + 0.0036*APTT).

A Comparison of the Epidemiological Characteristics Between Influenza and COVID-19 Patients: A Retrospective, Observational Cohort Study

Background and objective It is crucial to make early differentiation between coronavirus disease 2019 (COVID-19) and seasonal influenza infections at the time of a patient's presentation to the emergency department (ED). In light of this, this study aimed to identify key epidemiological, initial laboratory, and radiological differences that would enable early recognition during co-circulation. Methods This was a retrospective, observational cohort study. All adult patients presenting to our ED at the Watford General Hospital, UK, with a laboratory-confirmed diagnosis of COVID-19 (2019/20) or influenza (2018/19) infection were included in this study. Demographic, laboratory, and radiological data were collected. Binary logistic regression was employed to determine features associated with COVID-19 infection rather than influenza. Results Chest radiographs suggestive of viral pneumonitis and older age (≥80 years) were associated with increased odds of having COVID-19 [odds ratio (OR): 47.00, 95% confidence interval (CI): 21.63-102.13 and OR: 64.85, 95% CI: 19.96-210.69 respectively]. Low eosinophils (<0.02 x 109/L) were found to increase the odds of COVID-19 (OR: 2.12, 95% CI: 1.44-3.10, p<0.001). Conclusions Gaining awareness about the epidemiological, biological, and radiologic presentation of influenza-like illness can be useful for clinicians in ED to differentiate between COVID-19 and influenza. This study showed that older age, eosinopenia, and radiographic evidence of viral pneumonitis significantly increase the odds of having COVID-19 compared to influenza. Further research is needed to determine if these findings are affected by acquired or natural immunity.

Smell, taste and chemesthesis disorders in patients with the SARS-CoV-2 during Omicron variant pandemic in China

Chemosensory disorders (including smell, taste and chemesthesis) are among the established symptoms of COVID-19 infection; however, new data indicate that the changes in chemosensory sensation caused by COVID-19 may differ among populations and COVID-19 variants. To date, few studies have focused on the influence of the SARS-CoV-2 Omicron variant on qualitative changes and quantitative reductions in chemosensory function in China. We conducted a cross-sectional study of patients with COVID-19 caused by the Omicron variant, to investigate the prevalence of chemosensory disorders and chemosensory function before and during infection, using an online questionnaire. A total of 1245 patients with COVID-19 completed the survey. The prevalence rates of smell, taste, and chemesthesis disorders were 69.2%, 67.7%, and 31.4%, respectively. Our data indicate that sex, age, smoking, and COVID-19-related symptoms, such as lack of appetite, dyspnea, and fatigue, may be associated with chemosensory disorders during COVID-19. Self-rating of chemosensory function revealed that patients experienced a general decline in smell, taste, and chemesthesis function. Further longitudinal research studies are needed to generate additional data based on objective assessment and investigate the factors influencing chemosensory function in COVID-19.

Gastrointestinal symptoms of long COVID-19 related to the ectopic colonization of specific bacteria that move between the upper and lower alimentary tract and alterations in serum metabolites

BACKGROUND

Since the coronavirus disease 2019 (COVID-19) outbreak, many COVID-19 variants have emerged, causing several waves of pandemics and many infections. Long COVID-19, or long-term sequelae after recovery from COVID-19, has aroused worldwide concern because it reduces patient quality of life after rehabilitation. We aimed to characterize the functional differential profile of the oral and gut microbiomes and serum metabolites in patients with gastrointestinal symptoms associated with long COVID-19.

METHODS

We prospectively collected oral, fecal, and serum samples from 983 antibiotic-naïve patients with mild COVID-19 and performed a 3-month follow-up postdischarge. Forty-five fecal and saliva samples, and 25 paired serum samples were collected from patients with gastrointestinal symptoms of long COVID-19 at follow-up and from healthy controls, respectively. Eight fecal and saliva samples were collected without gastrointestinal symptoms of long COVID-19 at follow-up. Shotgun metagenomic sequencing of fecal samples and 2bRAD-M sequencing of saliva samples were performed on these paired samples. Two published COVID-19 gut microbiota cohorts were analyzed for comparison. Paired serum samples were analyzed using widely targeted metabolomics.

RESULTS

Mild COVID-19 patients without gastrointestinal symptoms of long COVID-19 showed little difference in the gut and oral microbiota during hospitalization and at follow-up from healthy controls. The baseline and 3-month samples collected from patients with gastrointestinal symptoms associated with long COVID-19 showed significant differences, and ectopic colonization of the oral cavity by gut microbes including 27 common differentially abundant genera in the Proteobacteria phylum, was observed at the 3-month timepoint. Some of these bacteria, including Neisseria, Lautropia, and Agrobacterium, were highly related to differentially expressed serum metabolites with potential toxicity, such as 4-chlorophenylacetic acid, 5-sulfoxymethylfurfural, and estradiol valerate.

CONCLUSIONS

Our study characterized the changes in and correlations between the oral and gut microbiomes and serum metabolites in patients with gastrointestinal symptoms associated with long COVID-19. Additionally, our findings reveal that ectopically colonized bacteria from the gut to the oral cavity could exist in long COVID-19 patients with gastrointestinal symptoms, with a strong correlation to some potential harmful metabolites in serum.

Retrospective Observational Study of Complete Blood Count (CBC) Parameters and ICU Mortality of COVID-19 Disease in Delta Variant and Omicron Variant in a Community-Based Hospital in New York City

BACKGROUND

Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) is the official name of COVID-19, a respiratory infection that had the first case reported from the Hubei province of China on December 8, 2019. This virus is the main etiological agent behind the most dreaded pandemic of pneumonia that has spread to the entire world in a brief period and continues to pose a threat. The first wave corresponded with the period from February 2020 to June 2020, the Delta variant occurred around the middle of June 2021 and the Omicron wave was reported from December 2021 to February 2022. Objective: This study aims to compare the Delta and the Omicron variants of COVID-19 infection in a community-based hospital in New York City considering the comparison of ICU admissions in both variants. We aim to study the comparison of complete blood count (CBC) parameters and inflammatory markers of patients admitted to ICU stratified by two waves of COVID-19 infection. We aim to analyze the association of CBC parameters at admission and the discharge during ICU stay in both variants. We also aim to study the association of CBC parameters at admission and discharge with ICU mortality in both variants.

METHODS

We conducted a retrospective observational study based on data from randomly selected hospitalized patients with COVID-19 in a community-based hospital in New York City during the Delta variant and the Omicron wave. A total of 211 patients COVID-19 positive from June to July 2021 (Delta variant) and 148 patients from December to February 2022 (Omicron wave) were included in the study. A comparison was done between the basic characteristics of patients with and without ICU admissions in both variants of COVID-19. We compared the relationship of different parameters of CBC (hemoglobin (Hgb), white blood count (WBC), lymphocytes, neutrophils, and platelets) on ICU admission and further analyzed any changes associated with ICU mortality. Logistic regression was performed to evaluate the relationship of different presenting CBCs on patients' disposition to ICU.  Result: A total of 211 patients (106 female) in the Delta wave (2021 variant) and 148 patients (80 female) in the Omicron wave (2022 variant) with an average ages of 60.9 ±18.10 (Delta variant) and 63.2 ± 19.10 (Omicron variant) were included in this study. There were 45 patients (21.3%) in the Delta wave and 42 patients (28.4%) in the Omicron wave were admitted to ICU. The average length of hospital stay was seven days in the Delta wave and nine days in the Omicron wave. No significant association was found between presenting cell count and ICU admission (p>0.05). Significant associations were found between different cell counts on admission and discharge and death in Delta waves except Hgb and platelets on admission. However, in the Omicron variant, a significant association was found only between WBC on admission and discharge, and Hgb and neutrophil on discharge with death in the univariate model.

CONCLUSION

 Comparative study of different clinical parameters between the Delta and the Omicron variants of COVID-19 with the correlation of ICU stay and mortality can be used as a beneficial modality in assessing the outcome of the disease.

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

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 regarding regional differences in prevalence as well as an estimate of the global prevalence of olfactory dysfunction based on 62 studies reporting information on 626,035 patients infected with the omicron variant. Our estimate of the omicron-induced prevalence of olfactory dysfunction in populations of European ancestry is 11.7%, while it is significantly lower in all other populations, ranging between 1.9% and 4.9%. When ethnic differences and population sizes are considered, the global prevalence of omicron-induced olfactory dysfunction in adults is estimated to be 3.7%. Omicron's effect on olfaction is twofold to tenfold lower than that of the alpha or delta variants according to previous meta-analyses and our analysis of studies that directly compared the prevalence of olfactory dysfunction between omicron and previous variants. The profile of the prevalence differences between ethnicities mirrors the results of a recent genome-wide association study that connected a gene locus encoding an odorant-metabolizing enzyme, UDP glycosyltransferase, to the extent of COVID-19-related loss of smell. Our analysis is consistent with the hypothesis that this enzyme contributes to the observed population differences.

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

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 62 studies reporting on 626,035 patients infected with the omicron variant. Our estimate of the omicron-induced prevalence of olfactory dysfunction in populations of European ancestry is 11.7%, while it is significantly lower in all other populations, ranging between 1.9% and 4.9%. When ethnic differences and population sizes are taken into account, the global prevalence of omicron-induced olfactory dysfunction in adults is estimated at 3.7%. Omicron’s effect on olfaction is twofold to tenfold 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.