Independent report

REACT-1 study of coronavirus transmission: March 2022 final results

Published 11 April 2022

Methodology

A representative cross-section of volunteers in England, aged 5 and over, tested themselves with swabs from 8 March to 31 March 2022 (inclusive). Swabs were analysed using polymerase chain reaction (PCR) for the presence of SARS-CoV-2.

Results

Over the 24 days of testing which form these round 19 findings of REACT-1, 6,902 samples tested positive from a total of 109,181 valid swab results, giving a weighted prevalence of 6.37% (6.21%, 6.53%) or 637 people per 10,000 infected. This compares to a weighted prevalence in the previous round, round 18 (8 February to 1 March 2022), of 2.88% (2.76%, 3.00%), and is the highest weighted prevalence observed throughout the REACT-1.

In round 19 we observed very high and increasing weighted prevalence at all ages ranging from 4.61% (4.20%, 5.07%) in those aged 75 years and over to 8.81% (7.89%, 9.82%) in those aged 5 to 11 years.

Weighted prevalence increased between round 18 and round 19 and showed a peak in round 17, a decrease in round 18 and a subsequent increase in round 19 at all ages.

Weighted prevalence in those aged 5 to 11 years in round 19 final was higher than in all other age groups and has more than doubled since round 18.

P-spline model fit to all REACT-1 data in 4 broad age groups separately showed rapidly increasing weighted prevalence between round 18 and round 19 final at all ages and:

• a possibly decreasing prevalence within round 19 in those aged 5 to 17 years
• a possibly plateauing prevalence in those aged 18 to 35 and 35 to 54 years
• a within-round increasing trend in those aged 55 years and over

At regional level, weighted prevalence in round 19 was very high and higher than in round 18 in all regions across England. The highest weighted prevalence in round 19 was 8.13% (7.59%,8.71%) in South West, and the lowest weighted prevalence observed was in the West Midlands at 5.28% (4.85%, 5.75%).

The highest weighted prevalence in round 19 was observed in:

• larger households including 2 persons at 6.03% (5.79%, 6.28%), 3 persons at 6.91% (6.54%, 7.30%), 4 persons at 7.13% (6.74%, 7.53%) and 5 persons at 6.97% (6.28%, 7.73%), compared to 5.26% (4.92%, 5.63%) in single-person households
• households with one or more children at 7.55% (7.22%, 7.89%) compared to 5.89% (5.71%, 6.08%) in households without children
• those having been in contact with a confirmed coronavirus (COVID-19) case at 17.8% (17.2%, 18.5%) or a suspected COVID-19 case at 12.5% (11.3%, 13.8%) compared to 4.00% (3.86%, 4.16%) for those without such contact
• those reporting not shielding at 6.64% (6.45%, 6.84%) compared to 6.00% (5.66%, 6.37%) in those reporting shielding
• those reporting classic COVID-19 symptoms (loss or change of sense of smell or taste, fever, new persistent cough) in the month prior to swabbing at 27.6% (26.7%, 28.5%) or other symptoms at 7.87% (7.43%, 8.33%) compared to 2.60% (2.47%, 2.74%) in those without symptoms

Of those who tested positive and reported on symptoms, 26.7% reported no symptoms in round 19 final compared to 28.6% in round 18.

Viral lineages were determined for 3,383 of 4,038 positive samples collected up to 22 March 2022, 89.7% corresponded with the Omicron BA.2 variant or its sub-lineages. The other determined samples corresponded with Omicron BA.1 (10.2%), BA.3 (0.16%) and the Delta AY.4 sub-lineage (0.003%).

Conclusion

During the 24 days covered by the period of this report, high levels of infection with SARS-CoV-2 were observed in England in March 2022.

The prevalence of SARS-CoV-2 infections overall was 637 per 10,000 people infected. The highest rates were observed regionally in the South West and nationally in those aged 5 to 11 years.

Of all the positive samples sequenced in this round, 99.9% all but one of those were Omicron variant, with one sub-lineage of Delta detected.