Hospital admission and emergency care attendance risk for SARS-CoV-2 delta (B.1.617.2) compared with alpha (B.1.1.7) variants of concern: a cohort study

COVID-19 Genomics UK (COG-UK) Consortium, Andrew Beggs

Research output: Contribution to journalArticlepeer-review

56 Downloads (Pure)


BACKGROUND: The SARS-CoV-2 delta (B.1.617.2) variant was first detected in England in March, 2021. It has since rapidly become the predominant lineage, owing to high transmissibility. It is suspected that the delta variant is associated with more severe disease than the previously dominant alpha (B.1.1.7) variant. We aimed to characterise the severity of the delta variant compared with the alpha variant by determining the relative risk of hospital attendance outcomes.

METHODS: This cohort study was done among all patients with COVID-19 in England between March 29 and May 23, 2021, who were identified as being infected with either the alpha or delta SARS-CoV-2 variant through whole-genome sequencing. Individual-level data on these patients were linked to routine health-care datasets on vaccination, emergency care attendance, hospital admission, and mortality (data from Public Health England's Second Generation Surveillance System and COVID-19-associated deaths dataset; the National Immunisation Management System; and NHS Digital Secondary Uses Services and Emergency Care Data Set). The risk for hospital admission and emergency care attendance were compared between patients with sequencing-confirmed delta and alpha variants for the whole cohort and by vaccination status subgroups. Stratified Cox regression was used to adjust for age, sex, ethnicity, deprivation, recent international travel, area of residence, calendar week, and vaccination status.

FINDINGS: Individual-level data on 43 338 COVID-19-positive patients (8682 with the delta variant, 34 656 with the alpha variant; median age 31 years [IQR 17-43]) were included in our analysis. 196 (2·3%) patients with the delta variant versus 764 (2·2%) patients with the alpha variant were admitted to hospital within 14 days after the specimen was taken (adjusted hazard ratio [HR] 2·26 [95% CI 1·32-3·89]). 498 (5·7%) patients with the delta variant versus 1448 (4·2%) patients with the alpha variant were admitted to hospital or attended emergency care within 14 days (adjusted HR 1·45 [1·08-1·95]). Most patients were unvaccinated (32 078 [74·0%] across both groups). The HRs for vaccinated patients with the delta variant versus the alpha variant (adjusted HR for hospital admission 1·94 [95% CI 0·47-8·05] and for hospital admission or emergency care attendance 1·58 [0·69-3·61]) were similar to the HRs for unvaccinated patients (2·32 [1·29-4·16] and 1·43 [1·04-1·97]; p=0·82 for both) but the precision for the vaccinated subgroup was low.

INTERPRETATION: This large national study found a higher hospital admission or emergency care attendance risk for patients with COVID-19 infected with the delta variant compared with the alpha variant. Results suggest that outbreaks of the delta variant in unvaccinated populations might lead to a greater burden on health-care services than the alpha variant.

FUNDING: Medical Research Council; UK Research and Innovation; Department of Health and Social Care; and National Institute for Health Research.

Original languageEnglish
Pages (from-to)35-42
Number of pages8
JournalThe Lancet Infectious Diseases
Issue number1
Early online date27 Aug 2021
Publication statusPublished - Jan 2022

Bibliographical note

Funding Information:
We acknowledge the national collaborative effort undertaken by the institutions participating in the COVID-19 Genomics UK (COG-UK) consortium that enables this national public health response. We thank the Hospital-onset COVID Team (Simon Collin and Efejiro Ashano) and NHS-Digital. We thank Lara Utsi for assisting with the linkage to the vaccination dataset. We thank Natalie Groves for work on the variant case definitions and supporting the genome classification process. We acknowledge the Public Health England DataLake, DataStore, and Second Generation Surveillance System teams for maintenance of the databases in which data are stored. This research was funded by the Medical Research Council (MRC; authors DDA and AMP: Unit Programme number MC_UU_00002/11; author SRS: Unit Programme number MC_UU_00002/10); and via a grant from the MRC UK Research and Innovation (UKRI)/Department of Health and Social Care National Institute for Health Research (NIHR) COVID-19 rapid response call (authors TN, AC, DDA, and AMP: grant reference MC_PC_19074). The COG-UK consortium is supported by funding from the MRC part of UKRI, the NIHR and Genome Research Limited, operating as the Wellcome Sanger Institute.

GD's employer, Public Health England, has received funding from GlaxoSmithKline for a research project related to seasonal influenza and antiviral treatment; this project preceded and had no relation to COVID-19, and GD had no role in and received no funding from the project. All other authors declare no competing interests.

Publisher Copyright:
Crown copyright © 2022 Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license.

ASJC Scopus subject areas

  • Infectious Diseases


Dive into the research topics of 'Hospital admission and emergency care attendance risk for SARS-CoV-2 delta (B.1.617.2) compared with alpha (B.1.1.7) variants of concern: a cohort study'. Together they form a unique fingerprint.

Cite this