BACKGROUND
Rapid transmission of the SARS-CoV-2 Omicron variant has led to record-breaking incidence
rates around the world. Sub-lineages have been detected in many countries with BA.1
replacing Delta and BA.2 replacing BA.1.
METHODS
The REal-time Assessment of Community Transmission-1 (REACT-1) study has tracked
SARS-CoV-2 infection in England using RT-PCR results from self-administered throat and nose
swabs from randomly-selected participants aged 5+ years. Rounds of data collection were
approximately monthly from May 2020 to March 2022.
RESULTS
In March 2022, weighted prevalence was 6.37% (N=109,181), more than twice that in
February 2022 following an initial Omicron peak in January 2022. Of the lineages
determined by viral genome sequencing, 3,382 (99.97%) were Omicron, including 346
(10.2%) BA.1, 3035 (89.7%) BA.2 and one (0.03%) BA.3 sub-lineage; the remainder (1, 0.03%)
was Delta AY.4. The BA.2 Omicron sub-lineage had a growth rate advantage (compared to
BA.1 and sub-lineages) of 0.11 (95% credible interval [CrI], 0.10, 0.11). Prevalence was
increasing overall (reproduction number R=1.07, 95% CrI, 1.06, 1.09), with the greatest
increase in those aged 55+ years (R=1.12, 95% CrI, 1.09, 1.14) among whom estimated
prevalence on March 31, 2022 was 8.31%, nearly 20-fold the median prevalence since May
1, 2020.
CONCLUSIONS
We observed unprecedented levels of SARS-CoV-2 infection in England in March 2022 and an
almost complete replacement of Omicron BA.1 by BA.2. The high and increasing prevalence
in older adults may increase hospitalizations and deaths despite high levels of vaccination.
(Funded by the Department of Health and Social Care in England.)