Résumé
Since the emergence of Omicron variant of SARS-CoV-2 in late 2021, a number of sub-lineages have arisen and circulated internationally. Little is known about the relative severity of Omicron sub-lineages BA.2.75, BA.4.6 and BQ.1. We undertook a case-control analysis to determine the clinical severity of these lineages relative to BA.5, using whole genome sequenced, PCR-confirmed infections, between 1 August 2022 to 27 November 2022, among those who presented to emergency care in England 14 days after and up to one day prior to the positive specimen. A total of 10,375 episodes were included in the analysis, of which 5,207 (50.2%) were admitted to hospital or died. Multivariable conditional regression analyses found no evidence for greater odds of hospital admission or death among those with BA.2.75 (OR= 0.96, 95% CI: 0.84 to 1.09), and BA.4.6 (OR= 1.02, 95% CI: 0.88 to 1.17) or BQ.1 (OR= 1.03, 95 % CI: 0.94 to 1.13) compared to BA.5. Future lineages may not follow the same trend and there remains a need for continued surveillance of COVID-19 variants and their clinical outcomes to inform the public health response.
Sujets)
Mort , COVID-19Résumé
Purpose The Gamma variant of SARS-CoV-2, first detected in travellers from Brazil, was found to have high transmissibility and virulence; following this finding, this paper aims to describe the epidemiology of Gamma cases in England from its first detection on 12 February 2021 to 31 August 2021. Methods The demographic analysis of Gamma cases was stratified by travel exposure. Travel-associated cases were further analysed by countries travelled from, stratified by categories set in place by the Red (highest risk countries), Amber, Green (lowest risk countries) travel policy, which was implemented from May to October 2021. Results There were 251 confirmed Gamma cases detected in England in the study period. 35.1% were imported, 5.6% were secondary, and 29.5% were not travel associated. Early cases were predominantly travel-associated, with later cases likely obtained through community transmission. 51.0% of travel-related cases were travellers from Amber countries, and 40.2% had at least one Red country in their journey. Conclusion The Gamma variant has not seen the same expansion as other variants such as Delta, most likely due to Delta out-competing community transmission of Gamma. Findings indicate the travel policy requiring quarantine for Red and Amber list travellers may have also contributed to preventing onward transmission of Gamma.
Résumé
Background The SARS-CoV-2 Omicron variant (B.1.1.529) has rapidly replaced the Delta variant (B.1.617.2) to become dominant in England. This epidemiological study assessed differences in transmissibility between the Omicron and Delta using two methods and data sources. Methods Omicron and Delta cases were identified through genomic sequencing, genotyping and S-gene target failure in England from 5-11 December 2021. Secondary attack rates for Omicron and Delta using named contacts and household clustering were calculated using national surveillance and contact tracing data. Logistic regression was used to control for factors associated with transmission. Findings Analysis of contact tracing data identified elevated secondary attack rates for Omicron vs Delta in household (15.0% vs 10.8%) and non-household (8.2% vs 3.7%) settings. The proportion of index cases resulting in residential clustering was twice as high for Omicron (16.1%) compared to Delta (7.3%). Transmission was significantly less likely from cases, or in named contacts, in receipt of three compared to two vaccine doses in household settings, but less pronounced for Omicron (aRR 0.78 and 0.88) compared to Delta (aRR 0.62 and 0.68). In non-household settings, a similar reduction was observed for Delta cases and contacts (aRR 0.84 and 0.51) but only for Omicron contacts (aRR 0.76, 95% CI: 0.58-0.93) and not cases in receipt of three vs two doses (aRR 0.95, 0.77-1.16). Interpretation Our study identified increased risk of onward transmission of Omicron, consistent with its successful global displacement of Delta. We identified a reduced effectiveness of vaccination in lowering risk of transmission, a likely contributor for the rapid propagation of Omicron.