High national prevalence of SARS-CoV-2 with regional variability in England, REACT-1 survey finds

By Dr. Sanchari Sinha Dutta, Ph.D.Feb 1 2021

The REACT-1 survey conducted in the United Kingdom demonstrates a high average prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in England during January 2021. The survey also indicates that a sustained reduction in infection prevalence is urgently needed to avoid burden on healthcare systems and reduce coronavirus disease 2019 (COVID-19)-related mortality. A detailed survey report is currently available on the medRxiv* preprint server.

Background

In England, a 3^rd national-wide lockdown was implemented in January 2021 to curb the rapid spread of SARS-CoV-2 infection and reduce the mortality rate. Simultaneously, an extensive vaccination program was launched for healthcare workers and people at higher risk of developing severe COVID-19.

REACT-1 survey, a community-level survey on COVID-19 prevalence was conducted using repeated cross-sectional analyses of random samples obtained from England's general population. In each round of the survey, respiratory swab samples and other COVID-19 related information were collected from 167,642 people.

The survey provided detailed information about SARS-CoV-2 prevalence in England between January 6 and January 22, 2021.

Important observations

According to the survey findings, about 2,282 of 167,642 samples tested positive for SARS-CoV-2, showing a prevalence of 1.57%. During the survey period, the reproductive number (a mathematical term indicating infectivity of a pathogen) was estimated to be 0.98. In general, the prevalence remained constant during the survey period, with a slightly increasing trend between January 6 and January 15. However, the prevalence appeared to decline afterward.

Compared to the 1^st nation-wide lockdown, a significantly lower prevalence was observed during the 3^rd lockdown. According to the scientists, this discrepancy may be associated with a higher level of mobility, the higher percentage of workplace and school attendees, and the higher infectivity of the new SARS-CoV-2 variant circulating during the 3^rd lockdown in England.

Prevalence of swab-positivity for each region of England estimated using a pspline (with a constant second-order random walk prior distribution) fit to all 8 rounds of data (only shown for the duration of round 8) with central 50% (dark grey) and 95% (light grey) posterior credible intervals. Points show daily estimated unweighted prevalence with vertical solid lines showing 95% confidence intervals.

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Furthermore, a variation in SARS-CoV-2 prevalence was observed at the regional level, with significantly decreasing prevalence in the South West region and increasing prevalence in East Midlands. At the regional level, the highest prevalence (2.8%) was observed in London. Moreover, in this region, more than 2% and 4% prevalence were observed in the elderly (age range: 55 years and above) and younger (age range: 13 – 24 years) population, respectively. This indicates a rapidly increasing prevalence in London and nearby regions.

Regional comparison of REACT-1 estimated prevalence using a p-spline with central 50% (dark grey, left axis) and 95% (light grey, left axis) posterior credible intervals and routine PCR positivity for England (red, right axis) averaged over 7 days, plotted at the midpoint of the interval.

At the national level, the highest prevalence (2.4%) was observed in the low-risk age group (18 – 24 years). However, the prevalence was also high among people aged 65 years and above.       

A significant correlation was observed between higher infection prevalence and family size, socioeconomic status of the neighborhood, and Black and Asian ethnicity. Compared to white people with a 1.4% prevalence, the prevalence in Black and Asian populations was estimated to be 3% and 2.8%, respectively. This indicates that these ethnic groups are at higher risk of SARS-CoV-2 infection.

The frequency of having a SARS-CoV-2-positive test result was significantly higher among healthcare workers, care home workers, and other frontline workers. This indicates a higher risk of occupational transmission of the virus.

Neighborhood prevalence of swab-positivity for round 8. Neighborhood prevalence calculated from nearest neighbors (the median number of neighbors within 30km in the study). Average neighborhood prevalence displayed for individual lower-tier local authorities. Regions: NE = North East, NW = North West, YH = Yorkshire and The Humber, EM = East Midlands, WM = West Midlands, EE = East of England, L = London, SE = South East, SW = South West. Data for unweighted point estimate of prevalence available in the supplementary data file.

Study significance

According to the survey findings, the prevalence of SARS-CoV-2 infection in England was exceptionally high in January 2021. This corresponds with the increased number of hospital and intensive care unit admissions and higher COVID-19-related mortality rate. Although a declining trend in infection prevalence was observed at the end of the survey period, the infection levels remain significantly higher than those observed during the 1^st lockdown.

According to the scientists, pressure on healthcare systems and the mortality rate will continue to increase unless a sustained reduction in infection prevalence is achieved. In this scenario, proper implementation of control measures is highly recommended.

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.