Independent report

REACT-1 study of coronavirus transmission: June 2021 final results

Published 10 August 2021

Applies to England

Methodology

A representative cross-section of volunteers in England, ages 5 and over, tested themselves in round 13 of REACT with swabs from 24 June to 12 July inclusive. Swabs were analysed using polymerase chain reaction (PCR) for the presence of SARs-CoV-2.

Results

Over the 19 days of testing in round 13 of REACT-1, 527 of 98,233 swab results were positive giving a weighted national prevalence of 0.63% (0.57%, 0.69%), or 63 people per 10,000 infected. This represents a greater than 4-fold increase when compared with prevalence during the previous round, round 12 (20 May to 7 June), when weighted prevalence was 0.15% (0.12%, 0.18%).

The period between round 12 and 13 showed evidence of exponential growth with an estimated doubling time of 15 days (13, 17), and a corresponding R number during this period of 1.28 (1.24, 1.31).

Exponential growth appeared to have slowed down during round 13, with an estimated doubling time of 25 days (lower credible interval 15 days) with a corresponding R of 1.19 (1.06, 1.32).

Other relevant findings reported in round 13 were as follows:

The number of infections increased in all regions of England, when compared with round 12. The largest increase was in London where prevalence increased more than 8-fold from 0.13% (0.08%, 0.20%) in round 12 to 0.94% (0.76%, 1.16%) in round 13.

In terms of age, there was a substantial increase in prevalence in all age groups under the age of 75 years, and especially at younger ages.

The highest weighted prevalence was among 13 to 17 year olds at 1.56% (1.25%, 1.95%) and 18 to 24 year olds at 1.56% (1.15%, 2.13%). For 13 to 17 years olds, this represents a 9-fold increase when compared with round 12 – 0.16% (0.08%, 0.31%).

Ethnicity, household size and local levels of deprivation appeared to jointly contribute to the risk of testing positive. The highest prevalence was observed:

• in people who self-reported Black ethnicity at 1.21% (0.75%, 1.93%) compared with 0.59% (0.53%, 0,65%) in people who self-reported White ethnicity
• in those in the largest households of 6 or more people at 1.35% (0.90%, 2.01%) compared with 0.44% (0.32%, 0.61%) and 0.44% (0.36%, 0.53%) in single and 2-person households respectively
• in participants living in the most deprived neighbourhoods at 0.82% (0.65%, 1.04%) compared with least deprived at 0.48% (0.39%, 0.59%)

Of the samples which were sequenced for variants, of SARS-CoV-2 (the virus causing COVID-19), 100% were the Delta variant, in comparison with round 12 where 78.3% were the Delta variant and remaining samples were the Alpha variant.

In round 13, vaccinated participants were substantially less likely to test positive for virus compared with those unvaccinated. The chance of testing positive was 3-fold greater in those who were unvaccinated at 1.21% (1.03%, 1.41%) when compared with those who had 2 doses of the vaccine (0.40% (0.34%, 0.48%)). The ratio of prevalence in those that were unvaccinated versus those that were vaccinated was similar to that observed in round 12.

Double-vaccinated people in the most recent round were estimated to have around 50% to 60% reduced risk of infection, including asymptomatic infection, compared with unvaccinated people.

Conclusion

During the period 24 June to 12 July (round 13 of REACT), the number of SARS-CoV-2 infections continued to rise exponentially when compared with the previous round from 20 May to 7 June, with 63 in 10,000 infected (1 in 170 people infected). The highest rates were observed regionally in London and in those aged 13 to 24 years nationally. All positive samples from this round that could be sequenced were found to be the Delta variant.