REACT-1 round 12 report: resurgence of SARS-CoV-2 infections in England associated with increased frequency of the Delta variant
File(s)react1_r12_preprint_final.pdf (1.88 MB)
Working paper
Author(s)
Type
Working Paper
Abstract
Background
England entered a third national lockdown from 6 January 2021 due to the COVID-19
pandemic. Despite a successful vaccine rollout during the first half of 2021, cases and
hospitalisations have started to increase since the end of May as the SARS-CoV-2 Delta
(B.1.617.2) variant increases in frequency. The final step of relaxation of COVID-19
restrictions in England has been delayed from 21 June to 19 July 2021.
Methods
The REal-time Assessment of Community Transmision-1 (REACT-1) study measures the
prevalence of swab-positivity among random samples of the population of England. Round
12 of REACT-1 obtained self-administered swab collections from participants from 20 May
2021 to 7 June 2021; results are compared with those for round 11, in which swabs were
collected from 15 April to 3 May 2021.
Results
Between rounds 11 and 12, national prevalence increased from 0.10% (0.08%, 0.13%) to
0.15% (0.12%, 0.18%). During round 12, we detected exponential growth with a doubling
time of 11 (7.1, 23) days and an R number of 1.44 (1.20, 1.73). The highest prevalence was
found in the North West at 0.26% (0.16%, 0.41%) compared to 0.05% (0.02%, 0.12%) in the
South West. In the North West, the locations of positive samples suggested a cluster in
Greater Manchester and the east Lancashire area. Prevalence in those aged 5-49 was 2.5
times higher at 0.20% (0.16%, 0.26%) compared with those aged 50 years and above at
0.08% (0.06%, 0.11%). At the beginning of February 2021, the link between infection rates
and hospitalisations and deaths started to weaken, although in late April 2021, infection
rates and hospital admissions started to reconverge. When split by age, the weakened link
between infection rates and hospitalisations at ages 65 years and above was maintained,
while the trends converged below the age of 65 years. The majority of the infections in the
younger group occurred in the unvaccinated population or those without a stated vaccine
history. We observed the rapid replacement of the Alpha (B.1.1.7) variant of SARS-CoV-2
with the Delta variant during the period covered by rounds 11 and 12 of the study.
Discussion
The extent to which exponential growth continues, or slows down as a consequence of the
continued rapid roll-out of the vaccination programme, including to young adults, requires
close monitoring. Data on community prevalence are vital to track the course of the epidemic
and inform ongoing decisions about the timing of further lifting of restrictions in England.
England entered a third national lockdown from 6 January 2021 due to the COVID-19
pandemic. Despite a successful vaccine rollout during the first half of 2021, cases and
hospitalisations have started to increase since the end of May as the SARS-CoV-2 Delta
(B.1.617.2) variant increases in frequency. The final step of relaxation of COVID-19
restrictions in England has been delayed from 21 June to 19 July 2021.
Methods
The REal-time Assessment of Community Transmision-1 (REACT-1) study measures the
prevalence of swab-positivity among random samples of the population of England. Round
12 of REACT-1 obtained self-administered swab collections from participants from 20 May
2021 to 7 June 2021; results are compared with those for round 11, in which swabs were
collected from 15 April to 3 May 2021.
Results
Between rounds 11 and 12, national prevalence increased from 0.10% (0.08%, 0.13%) to
0.15% (0.12%, 0.18%). During round 12, we detected exponential growth with a doubling
time of 11 (7.1, 23) days and an R number of 1.44 (1.20, 1.73). The highest prevalence was
found in the North West at 0.26% (0.16%, 0.41%) compared to 0.05% (0.02%, 0.12%) in the
South West. In the North West, the locations of positive samples suggested a cluster in
Greater Manchester and the east Lancashire area. Prevalence in those aged 5-49 was 2.5
times higher at 0.20% (0.16%, 0.26%) compared with those aged 50 years and above at
0.08% (0.06%, 0.11%). At the beginning of February 2021, the link between infection rates
and hospitalisations and deaths started to weaken, although in late April 2021, infection
rates and hospital admissions started to reconverge. When split by age, the weakened link
between infection rates and hospitalisations at ages 65 years and above was maintained,
while the trends converged below the age of 65 years. The majority of the infections in the
younger group occurred in the unvaccinated population or those without a stated vaccine
history. We observed the rapid replacement of the Alpha (B.1.1.7) variant of SARS-CoV-2
with the Delta variant during the period covered by rounds 11 and 12 of the study.
Discussion
The extent to which exponential growth continues, or slows down as a consequence of the
continued rapid roll-out of the vaccination programme, including to young adults, requires
close monitoring. Data on community prevalence are vital to track the course of the epidemic
and inform ongoing decisions about the timing of further lifting of restrictions in England.
Date Issued
2021-06-17
Citation
2021
Copyright Statement
© 2021 The Author(s)
Publication Status
Published