Background: England experienced a third wave of the COVID-19 epidemic from end May
2021 coinciding with the rapid spread of Delta variant. Since then, the population eligible for
vaccination against COVID-19 has been extended to include all 12-15-year-olds, and a
booster programme has been initiated among adults aged 50 years and over, health care
and care home workers, and immunocompromised people. Meanwhile, schoolchildren have
returned to school often with few COVID-19-related precautions in place.
Methods: In the REal-time Assessment of Community Transmission-1 (REACT-1) study,
throat and nose swabs were sent to non-overlapping random samples of the population
aged 5 years and over in England. We analysed prevalence of SARS-CoV-2 using reverse
transcription-polymerase chain reaction (RT-PCR) swab-positivity data from REACT-1 round
14 (between 9 and 27 September 2021). We combined results for round 14 with round 13
(between 24 June and 12 July 2021) and estimated vaccine effectiveness and prevalence of
swab-positivity among double-vaccinated individuals. Unlike all previous rounds, in round 14,
we switched from dry swabs transported by courier on a cold chain to wet swabs using
saline. Also, at random, 50% of swabs (not chilled until they reached the depot) were
transported by courier and 50% were sent through the priority COVID-19 postal service.
Results: We observed stable or rising prevalence (with an R of 1.03 (0.94, 1.14) overall)
during round 14 with a weighted prevalence of 0.83% (0.76%, 0.89%). The highest weighted
prevalence was found in children aged 5 to 12 years at 2.32% (1.96%, 2.73%) and 13 to 17
years at 2.55% (2.11%, 3.08%). All positive virus samples analysed correspond to the Delta
variant or sub-lineages of Delta with one instance of the E484K escape mutation detected.
The epidemic was growing in those aged 17 years and under with an R of 1.18 (1.03, 1.34),
but decreasing in those aged 18 to 54 years with an R of 0.81 (0.68, 0.97). For all
participants and all vaccines combined, vaccine effectiveness against infection (rounds 13
and 14 combined) was estimated to be 62.8% (49.3%, 72.7%) after two doses compared to
unvaccinated people when adjusted for round, age, sex, index of multiple deprivation, region
and ethnicity; the adjusted estimate was 44.8% (22.5%, 60.7%) for AstraZeneca and 71.3%
(56.6%, 81.0%) for Pfizer-BioNTech, and for all vaccines combined it was 66.4% (49.6%,
77.6%) against symptomatic infection (one or more of 26 surveyed symptoms in month
prior). Across rounds 13 and 14, weighted prevalence of swab-positivity was 0.55% (0.50%,
0.61%) for those who received their second dose 3-6 months before their swab compared to
0.35% (0.31%, 0.40%) for those whose second dose was within 3 months of their swab.
However, the prevalence was lower in those with one or two doses of vaccine than in
unvaccinated individuals at 1.76% (1.60%, 1.95%). In round 14, age group, region, key
worker status, and household size jointly contributed to the risk of higher prevalence of
swab-positivity.
Discussion: In September 2021 infections were increasing exponentially in the 5-to-17-year
age group coinciding with the start of the autumn school term in England. Relatively few
schoolchildren aged 5 to 17 years have been vaccinated in the UK though single doses are
now being offered to those aged 12 years and over. In adults, the higher prevalence of
swab-positivity following two doses of vaccine within 3 to 6 months supports the use of a
booster vaccine. It is important that the vaccination programme maintains high coverage and
reaches children and unvaccinated or partially vaccinated adults to reduce transmission and
associated disruptions to work and education.