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A descriptive comparison of admission characteristics between pandemic waves and multivariable analysis of the association of the Alpha variant (B.1.1.7 lineage) of SARS-CoV-2 with disease severity in inner London

Research output: Contribution to journalArticlepeer-review

Luke B. Snell, Wenjuan Wang, Adela Alcolea-Medina, Themis Charalampous, Rahul Batra, Leonardo de Jongh, Finola Higgins, COG-UK HOCI Investigators, Gaia Nebbia, Yanzhong Wang, Jonathan Edgeworth, Vasa Curcin

Original languageEnglish
JournalBMJ Open
Accepted/In press7 Oct 2021

King's Authors


Background: The Alpha variant (B.1.1.7 lineage) of SARS-CoV-2 emerged and became the dominant circulating variant in the UK in late 2020. Current literature is unclear on whether the Alpha variant is associated with increased severity. We linked clinical data with viral genome sequence data to compare admitted cases between SARS-CoV-2 waves in London, and to investigate the association between Alpha variant and the severity of disease.

Methods: Clinical, demographic, laboratory and viral sequence data from electronic health record (EHR) systems was collected for all cases with a positive SARS-CoV-2 RNA test between March 13th 2020 and February 17th 2021 in a multi-site London healthcare institution. Multivariate analysis using logistic regression assessed risk factors for severity as defined by hypoxia at admission.

Results: There were 5810 SARS-CoV-2 RNA positive cases of which 2341 were admitted (838 in wave one and 1503 in wave two). Both waves had a temporally aligned rise in nosocomial cases (96 in wave one, 137 in wave two). The Alpha variant was first identified on 15th November 2020 and increased rapidly to comprise 400/472 (85%) of sequenced isolates from admitted cases in wave two. A multivariate analysis identified risk factors for severity on admission, such as age (OR 1.02 [CI 1.01-1.03] for every year older, p<0.001), obesity (OR 1.70 [CI 1.28-2.26], p<0.001) and infection with the Alpha variant (OR 1.68 [CI 1.26-2.24], p<0.001).

Conclusions: Our analysis is the first in hospitalised cohorts to show increased severity of disease associated with the Alpha variant. The number of nosocomial cases was similar in both waves despite the introduction of many infection control interventions before wave two.

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