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18th May 2021
The study employs two methods of identifying the community prevalence of COVID-19; antigen testing obtained via self-swab testing and lateral flow tests using blood samples, to detect for COVID-19 antibodies. Thus REACT-1 is in effect, a surveillance program to help track patterns of the epidemic which could not easily be achieved based solely on either routine testing, hospitalisations or deaths. The details of the most recent self-reported swab testing results (round 11) cover the period from the middle of April 2021 to the beginning of May 2021. A further analysis of REACT-1 involved genomic testing of a sample of positive swabs to determine the most prevalent circulating COVID-19 variant.
Based on a sample of 127,408 random swab tests, 115 were found to be positive, giving a weighted prevalence of 0.10% (95% CI 0.08 – 0.13%). For comparative purposes, the first samples for the REACT-1 study were obtained between May and June 2020 and with a sample of 120,620 swabs, identified 159 positives, giving a weighted prevalence of 0.16%. Moreover, when compared with round 10 (March – 30 April 2021), when the weighted prevalence was 0.20%, cases have reduced by 50%. A large reduction was seen in those aged 55 to 64, where the prevalence dropped from 0.17% to 0.06% between rounds 10 and 11. In contrast, the prevalence among those aged 25 – 34 years had increased slightly (0.21% vs 0.18%, round 11 vs round 10). Furthermore, there was also a slight increase among those of Asian ethnicity, rising from 0.27% to 0.31% (round 10 vs round 11). In fact, the authors calculated that compared to those of white ethnicity, the odds of testing positive for someone of Asian ethnicity was 1.88 (95% CI 0.95 – 3.74). Genomic analysis of 26 of the 115 positive swabs revealed that the most common variant (92.3%) was B.1.1.7, the variant first identified in the UK, with the remaining samples comprising the B.1.617.2 (the Indian variant).
The authors were encouraged that the data indicated a 50% reduction in positive swabs compared to round 10 with a significant decrease among those aged 55 to 64 years, probably reflecting increased rates of vaccination. However, the slight uptick in rates among 25–34-year-olds was likely due to greater contact as restrictions eased. With an increase observed in those of Asian ethnicity, the data suggests that the virus continues to spread within this community.
1st December 2020
The REal-time Assessment of Community Transmission-1 (REACT-1), which was established by a team at Imperial College, London, has been collecting monthly and random data since May 2020. The study is designed to examine time trends in the prevalence of positive, self-administered nose and throat swab tests in England. The collected data can then be used to estimate the prevalence of COVID-19 by age and in different regions of the England.
The latest data show that there were 821 positive cases from 105,123 swab tests (0.78%), giving a weighted prevalence of 0.96% This is approximately 30% lower than the figure observed during the last period (1.32%) collected between 26 October and 2 November 2020. Using these results, the team have estimated that the R value is 0.88. The information on positivity for the different regions of England show that there has been a reduction of more than 50% in the North West and North East (where levels were previously much higher) though little change in the East and West Midlands and London. Based on their findings, the authors estimate a national prevalence of 0.96%, equivalent to approximately 720,000 infections in England on any one day.
However, the study is not all good news. There appears to be an increased prevalence in those aged 5 to 17 years, i.e., school children. Additionally, the data show that there is no evidence of decline among people of Black and Asian ethnicity, with the latter group having a much higher odds of testing positive (odds ratio = 1.72) compared with White individuals. There were also increased odds of testing positive among those from the most socially deprived areas and among health and care workers.
The authors conclude by noting that while the prevalence of infection appears to be reducing, it is still high at roughly 1% of the population and that measures will be needed to suppress levels further such as widespread vaccination.
Imperial College. REACT-1 round 7 interim report: fall in prevalence of swab-positivity in England during national lockdown.
30th October 2020
The REACT-1 study was established in May 2020 by a team from Imperial College, London and involves obtaining nose and throat swabs from non-overlapping random samples of the population of England, at ages 5 years and above, obtained from a list of GP registered patients as the sampling frame. The swabs are sent to patient’s homes and collected via courier and PCR tested. To date there have been five rounds of data collection and the team use this data to analyse trends in swab positivity and provide weighted and unweighted population estimates. The latest publication includes data from round 6, collected from 16 to 25 October 2020 and is therefore as current as possible.
In the latest round there were 863 positive swabs from a total of 85,971, giving an unweighted prevalence of 1% and a weighted prevalence of 1.28% (95% CI 1.15–1.41%). Compared to round 5 (18 September to 5 October 2020) where the weighted prevalence of was 0.60%, the latest figures suggest that the prevalence of COVID-19 has more than doubled. Putting the data into perspective, the authors estimate that around 960,000 individuals have the virus on any one day and that this will lead to approximately 96,000 new infections per day. Interestingly, this latest weighted prevalence is the highest recorded compared to earlier rounds. For instance, the paper reports that in round 1 (1 May to 1 April 2020), the weighted prevalence was 0.16%. Additionally, the latest figures indicate that the prevalence was highest in Yorkshire and the Humber at 2.72% and lowest in the East of England at 0.55%. Epidemic growth is no longer fastest in the North of England but is increasing in the South East, East of England, London and the South West. Furthermore, prevalence has increased across all age groups with the greatest increase now among those aged 55–64, up threefold from round 5 although the highest weighted prevalence remains in the 18–24-year-olds at 2.25% an increase from 1.59% in round 5.
This increased prevalence gave an average R number of the period of rounds 5 and 6 of 1.20. The authors note that their most recent data suggests a national doubling of infection rates every 9 days and that this corresponds to an R value of 1.56. They conclude by stating that the epidemic has now reached a critical stage and that it is time to introduce more stringent measures to control the virus and thus avoid more hospital admissions and deaths.
Riley S et al. High prevalence of SARS-CoV-2 positivity and increasing R number in England during October 2020: REACT-1 round 6 interim report. MedRxiv 2020. https://doi.org/10.1101/2020.09.30.20204727
1st October 2020
Although previous reports from the REACT-1 team reported falls in the prevalence of COVID-19 between May and early August, by mid-August, they detected an upturn in the rate of infection and estimated the R value to be around 1.7. In their latest report, which covers the period from 18 to 26 September, the numbers suggest that there is some indication that the rate of increase in the prevalence may have slowed. The REACT-1 study uses repeated random samples of the population between the ages of 5 and over-using the NHS list of patients registered with a GP. Identified individuals are contacted by post and asked to complete a registration questionnaire and are provided with a self-administered swab kit which are collected from participants and tested using PCR for the presence of the virus. The team calculate the prevalence as a ratio of positive tests to overall tests and correct this figure for age, sex, region, ethnicity.
The latest report summarises the findings from the first four rounds and interim data for the 5th round. To date over 680,000 swabs have been tested and for the most recent period, there were 363 positive tests from a sample of 84,610, giving a weighted prevalence of 0.55%. This figure represents an upward trend and is the highest prevalence since the beginning of the study. It allowed the authors to estimate a doubling time of 10.6 days, which corresponds to an R number of 1.47 and a prevalence of over 1 in 200 across the population of England.
The authors suggest that the data indicates the epidemic now reflects community transmission rather than through hospitals or care homes and concluded that there is an urgent need to redouble efforts to reduce community transmission.
Riley S et al. High prevalence of SARS-CoV-2 swabs positivity in England during September 2020: Interim report of round 5 of REACT-1 study.