REACT-1 study of coronavirus transmission: February 2021 final results
Updated 23 April 2021
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Methodology
A representative cross-section of volunteers tested themselves with swabs from 4 February to 23 February inclusive. Swabs were analysed using polymerase chain reaction (PCR).
Results
Swab results reported for the period 4 February to 12 February are referred to as round 9a. Swab results reported for the period 13 February to 23 February are referred to as round 9b. Round 9 results are also compared with round 8 (6 January to 22 January) results.
REACT-1 round 9 (4 February to 23 February) included 165,456 individuals with a valid swab result of whom 689 tested positive, giving a weighted prevalence overall of 0.49% (0.44%, 0.55%), down by over two thirds from 1.57% (1.49%, 1.66%) in round 8 (6 January to 22 January). Over the 11 days of testing for round 9b (13 February to 23 February), out of 78,047 swab results, 301 were positive, giving an overall weighted prevalence of 0.47% (95% CI, 0.40%, 0.55%) or 47 people per 10,000 infected. This represents a small decrease from round 9a (4 February to 12 February) where 0.51%, or 51 per 10,000 people were infected.
Across the results for the latter half of round 8 (16 January to 22 January) and first half of round 9 (4 February to 12 February), a halving time of 15 days has been estimated, corresponding to R of 0.73 (0.69, 0.76). There was also evidence of decline over the period of round 9a and 9b with an estimated halving time of 31 days and a corresponding R of 0.86 (0.76, 0.97). A slowing in the rate of decline has been observed.
From round 8 (6 January to 22 January) to round 9 (4 February to 23 February) there was a decline of at least 50% in prevalence in all age groups. In round 9b (13 February to 23 February) prevalence varied from 0.21% in those aged 65 and over, to 0.71% in those aged 13 to 17 years.
Between rounds 8 (6 January to 22 January) and 9 (4 February to 23 February), regional prevalence fell in seven of the nine regions with smaller apparent falls in Yorkshire and The Humber, and in North East. However, between rounds 9a (4 February to 12 February) and 9b (13 February to 23 February), while there were apparent falls in North East, North West, East of England and South West, and no apparent change in Yorkshire and The Humber, there were apparent rises in London, South East, East Midlands and West Midlands.
In round 8 (6 January to 22 January), unweighted prevalence among Bangladeshi participants was very high at 6.1% (4.0%, 9.3%) compared to 1.2% (1.2%, 1.3%) in white participants. However unweighted prevalence in Bangladeshi participants fell to 0.85% (0.29%, 2.5%) in round 9 (unweighted prevalence for Bangladeshi participants reported because of small numbers of positives in round 9). In round 9 (4 February to 23 February), the highest weighted prevalence was amongst Pakistani participants at 2.1% (1.0%, 4.2%) compared with white participants at 0.41% (0.37%, 0.46%).
Healthcare workers and care home workers had higher adjusted odds of infection at 1.48 (1.25, 1.77) in round 8 and 1.37 (1.02, 1.86) in round 9 compared with other workers. Higher adjusted odds were seen in participants who worked in public transport at 2.17 (1.58, 2.97) in round 8, and 2.14 (1.20, 3.83) in round 9, compared with those who did not; higher adjusted odds were also seen in those working in education, school, nursery or childcare at 1.20 (1.03, 1.39) in round 8 and 1.43 (1.07, 1.91) in round 9 compared with participants not working in those settings. Lower adjusted odds of swab-positivity were seen among those not currently required to work outside their home at 0.67 (0.61, 0.74) in round 8 and 0.64 (0.54, 0.76) in round 9 compared with those currently required to work outside their home.
Conclusion
During the period 13 February to 23 February, SARS-CoV-2 virus was circulating with a lower prevalence than between 4 February to 12 February with 47 in 10,000 infected.
Subsequent rounds of REACT-1 will allow further accurate assessment of trends in prevalence and transmission.