Household transmission of COVID-19 cases associated with SARS-CoV-2 delta variant (B.1.617.2): national case-control study

Allen, Hester, Vusirikala, Amoolya, Flannagan, Joe, Twohig, Katherine A., Zaidi, Asad, Chudasama, Dimple, Lamagni, Theresa, Groves, Natalie, Turner, Charlie, Rawlinson, Christopher, Lopez-Bernal, Jamie, Harris, Ross, Charlett, Andre, Dabrera, Gavin, Kall, Meaghan, The COVID-19 Genomics UK (COG-UK) Consortium, , Bashton, Matthew, Nelson, Andrew, Smith, Darren, Young, Greg and McCann, Clare (2022) Household transmission of COVID-19 cases associated with SARS-CoV-2 delta variant (B.1.617.2): national case-control study. The Lancet Regional Health - Europe, 12. p. 100252. ISSN 2666-7762

1-s2.0-S2666776221002386-main.pdf - Published Version
Available under License Creative Commons Attribution Non-commercial No Derivatives 4.0.

Download (131kB) | Preview
Official URL:


Background: The SARS-CoV-2 Delta variant (B.1.617.2), first detected in India, has rapidly become the dominant variant in England. Early reports suggest this variant has an increased growth rate suggesting increased transmissibility. This study indirectly assessed differences in transmissibility between the emergent Delta variant compared to the previously dominant Alpha variant (B.1.1.7). Methods: A matched case-control study was conducted to estimate the odds of household transmission (≥ 2 cases within 14 days) for Delta variant index cases compared with Alpha cases. Cases were derived from national surveillance data (March to June 2021). One-to-two matching was undertaken on geographical location of residence, time period of testing and property type, and a multivariable conditional logistic regression model was used for analysis. Findings: In total 5,976 genomically sequenced index cases in household clusters were matched to 11,952 sporadic index cases (single case within a household). 43.3% (n=2,586) of cases in household clusters were confirmed Delta variant compared to 40.4% (n= 4,824) of sporadic cases. The odds ratio of household transmission was 1.70 among Delta variant cases (95% CI 1.48-1.95, p <0.001) compared to Alpha cases after adjusting for age, sex, ethnicity, index of multiple deprivation (IMD), number of household contacts and vaccination status of index case. Interpretation: We found evidence of increased household transmission of SARS-CoV-2 Delta variant, potentially explaining its success at displacing Alpha variant as the dominant strain in England. With the Delta variant now having been detected in many countries worldwide, the understanding of the transmissibility of this variant is important for informing infection prevention and control policies internationally.

Item Type: Article
Additional Information: Funding information: We would like to thank all the staff of the Public Health England COVID-19 National Epidemiology Cell, in particular Simon Thelwall and Mary Sinnathamby for their role in genomic surveillance. We would also like to thank the staff of the Public Health England (PHE) Geographic Information System (GIS) team for continuous facilitation of the residential property classification of cases. We thank the Wellcome Sanger Institute and other laboratories involved in whole genome sequencing of COVID-19 samples; and we thank the UK Variant Technical Group for advice and feedback in developing this study. Matthew Bashton, Andrew Nelson, Darren Smith, Greg Young and Clare McCann are member of the COVID-19 Genomics UK (COG-UK) Consortium.
Uncontrolled Keywords: COVID-19; SARS-CoV-2; variant; Delta,household; transmission; England
Subjects: C700 Molecular Biology, Biophysics and Biochemistry
Department: Faculties > Health and Life Sciences > Applied Sciences
Depositing User: Elena Carlaw
Date Deposited: 21 Jul 2022 16:19
Last Modified: 21 Jul 2022 16:30

Actions (login required)

View Item View Item


Downloads per month over past year

View more statistics