Background: The third wave of COVID-19 in England coincided with the rapid spread of the
Delta variant of SARS-CoV-2 from the end of May 2021. Case incidence data from the
national testing programme (Pillar 2) in England may be affected by changes in testing
behaviour and other biases. Community surveys may provide important contextual
information to inform policy and the public health response.
Methods: We estimated patterns of community prevalence of SARS-CoV-2 infection in
England using RT-PCR swab-positivity, demographic and other risk factor data from round
15 (interim) of the REal-time Assessment of Community Transmission-1 (REACT-1) study
(round 15a, carried out from 19 to 29 October 2021). We compared these findings with those
from round 14 (9 to 27 September 2021).
Results: During mid- to late-October 2021 (round 15a) weighted prevalence was 1.72%
(1.61%, 1.84%) compared to 0.83% (0.76%, 0.89%) in September 2021 (round 14). The
overall reproduction number (R) from round 14 to round 15a was 1.12 (1.11, 1.14) with
increases in prevalence over this period (September to October) across age groups and
regions except Yorkshire and The Humber. However, within round 15a (mid- to late-October)
there was evidence of a fall in prevalence with R of 0.76 (0.65, 0.88). The highest weighted
prevalence was observed among children aged 5 to 12 years at 5.85% (5.10%, 6.70%) and
13 to 17 years at 5.75% (5.02%, 6.57%). At regional level, there was an almost four-fold
increase in weighted prevalence in South West from round 14 at 0.59% (0.43%,0.80%) to
round 15a at 2.18% (1.84%, 2.58%), with highest smoothed prevalence at subregional level
also found in South West in round 15a. Age, sex, key worker status, and presence of
children in the home jointly contributed to the risk of swab-positivity. Among the 126
sequenced positive swabs obtained up until 23 October, all were Delta variant; 13 (10.3%)
were identified as the AY.4.2 sub-lineage.
Discussion: We observed the highest overall prevalence of swab-positivity seen in the
REACT-1 study in England to date in round 15a (October 2021), with a two-fold rise in
swab-positivity from round 14 (September 2021). Despite evidence of a fall in prevalence
from mid- to late-October 2021, prevalence remains high, particularly in school-aged
children, with evidence also of higher prevalence in households with one or more children.
Thus, vaccination of children aged 12 and over remains a high priority (with possible
extension to children aged 5-12) to help reduce within-household transmission and
disruptions to education, as well as among adults, to lessen the risk of serious disease
among those infected.