Imperial College London

Steven Riley

Faculty of MedicineSchool of Public Health

Professor of Infectious Disease Dynamics
 
 
 
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Contact

 

+44 (0)20 7594 2452s.riley

 
 
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Location

 

UG8Medical SchoolSt Mary's Campus

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Summary

 

Publications

Publication Type
Year
to

226 results found

Ainslie KEC, Riley S, 2022, Is annual vaccination best? A modelling study of influenza vaccination strategies in children., Vaccine, Vol: 40, Pages: 2940-2948

INTRODUCTION: Annual vaccination of children against influenza is a key component of vaccination programs in many countries. However, past infection and vaccination may affect an individual's susceptibility to infection. Little research has evaluated whether annual vaccination is the best strategy. Using the United Kingdom as our motivating example, we developed a framework to assess the impact of different childhood vaccination strategies, specifically annual and biennial (every other year), on attack rate and expected number of infections. METHODS AND FINDINGS: We present a multi-annual, individual-based, stochastic, force of infection model that accounts for individual exposure histories and disease/vaccine dynamics influencing susceptibility. We simulate birth cohorts that experience yearly influenza epidemics and follow them until age 18 to determine attack rates and the number of infections during childhood. We perform simulations under baseline conditions, with an assumed vaccination coverage of 44%, to compare annual vaccination to no and biennial vaccination. We relax our baseline assumptions to explore how our model assumptions impact vaccination program performance. At baseline, we observed less than half the number of infections between the ages 2 and 10 under annual vaccination in children who had been vaccinated at least half the time compared to no vaccination. When averaged over all ages 0-18, the number of infections under annual vaccination was 2.07 (2.06, 2.08) compared to 2.63 (2.62, 2.64) under no vaccination, and 2.38 (2.37, 2.40) under biennial vaccination. When we introduced a penalty for repeated exposures, we observed a decrease in the difference in infections between the vaccination strategies. Specifically, the difference in childhood infections under biennial compared to annual vaccination decreased from 0.31 to 0.04 as exposure penalty increased. CONCLUSION: Our results indicate that while annual vaccination averts more childhood infect

Journal article

Whitaker M, Elliott J, Chadeau M, Riley S, Darzi A, Cooke G, Ward H, Elliott Pet al., 2022, Persistent COVID-19 symptoms in a community study of 606,434 people in England, Nature Communications, Vol: 13, ISSN: 2041-1723

Long COVID remains a broadly defined syndrome, with estimates of prevalence and duration varying widely. We use data from rounds 3–5 of the REACT-2 study (n=508,707; September 2020 – February 2021), a representative community survey of adults in England, and replication data from round 6 (n=97,717; May 2021) to estimate the prevalence and identify predictors of persistent symptoms lasting 12 weeks or more; and unsupervised learning to cluster individuals by reported symptoms. At 12 weeks in rounds 3–5, 37.7% experienced at least one symptom, falling to 21.6% in round 6. Female sex, increasing age, obesity, smoking, vaping, hospitalisation with COVID-19, deprivation, and being a healthcare worker are associated with higher probability of persistent symptoms in rounds 3–5, and Asian ethnicity with lower probability. Clustering analysis identifies a subset of participants with predominantly respiratory symptoms. Managing the long-term sequelae of COVID-19 will remain a major challenge for affected individuals and their families and for health services.

Journal article

Cramer EY, Ray EL, Lopez VK, Bracher J, Brennen A, Castro Rivadeneira AJ, Gerding A, Gneiting T, House KH, Huang Y, Jayawardena D, Kanji AH, Khandelwal A, Le K, Mühlemann A, Niemi J, Shah A, Stark A, Wang Y, Wattanachit N, Zorn MW, Gu Y, Jain S, Bannur N, Deva A, Kulkarni M, Merugu S, Raval A, Shingi S, Tiwari A, White J, Abernethy NF, Woody S, Dahan M, Fox S, Gaither K, Lachmann M, Meyers LA, Scott JG, Tec M, Srivastava A, George GE, Cegan JC, Dettwiller ID, England WP, Farthing MW, Hunter RH, Lafferty B, Linkov I, Mayo ML, Parno MD, Rowland MA, Trump BD, Zhang-James Y, Chen S, Faraone SV, Hess J, Morley CP, Salekin A, Wang D, Corsetti SM, Baer TM, Eisenberg MC, Falb K, Huang Y, Martin ET, McCauley E, Myers RL, Schwarz T, Sheldon D, Gibson GC, Yu R, Gao L, Ma Y, Wu D, Yan X, Jin X, Wang Y-X, Chen Y, Guo L, Zhao Y, Gu Q, Chen J, Wang L, Xu P, Zhang W, Zou D, Biegel H, Lega J, McConnell S, Nagraj VP, Guertin SL, Hulme-Lowe C, Turner SD, Shi Y, Ban X, Walraven R, Hong Q-J, Kong S, van de Walle A, Turtle JA, Ben-Nun M, Riley S, Riley P, Koyluoglu U, DesRoches D, Forli P, Hamory B, Kyriakides C, Leis H, Milliken J, Moloney M, Morgan J, Nirgudkar N, Ozcan G, Piwonka N, Ravi M, Schrader C, Shakhnovich E, Siegel D, Spatz R, Stiefeling C, Wilkinson B, Wong A, Cavany S, España G, Moore S, Oidtman R, Perkins A, Kraus D, Kraus A, Gao Z, Bian J, Cao W, Lavista Ferres J, Li C, Liu T-Y, Xie X, Zhang S, Zheng S, Vespignani A, Chinazzi M, Davis JT, Mu K, Pastore Y Piontti A, Xiong X, Zheng A, Baek J, Farias V, Georgescu A, Levi R, Sinha D, Wilde J, Perakis G, Bennouna MA, Nze-Ndong D, Singhvi D, Spantidakis I, Thayaparan L, Tsiourvas A, Sarker A, Jadbabaie A, Shah D, Della Penna N, Celi LA, Sundar S, Wolfinger R, Osthus D, Castro L, Fairchild G, Michaud I, Karlen D, Kinsey M, Mullany LC, Rainwater-Lovett K, Shin L, Tallaksen K, Wilson S, Lee EC, Dent J, Grantz KH, Hill AL, Kaminsky J, Kaminsky K, Keegan LT, Lauer SA, Lemaitre JC, Lessler J, Meredith HR, Perez-Saez J, Shah S, Smithet al., 2022, Evaluation of individual and ensemble probabilistic forecasts of COVID-19 mortality in the United States., Proc Natl Acad Sci U S A, Vol: 119

SignificanceThis paper compares the probabilistic accuracy of short-term forecasts of reported deaths due to COVID-19 during the first year and a half of the pandemic in the United States. Results show high variation in accuracy between and within stand-alone models and more consistent accuracy from an ensemble model that combined forecasts from all eligible models. This demonstrates that an ensemble model provided a reliable and comparatively accurate means of forecasting deaths during the COVID-19 pandemic that exceeded the performance of all of the models that contributed to it. This work strengthens the evidence base for synthesizing multiple models to support public-health action.

Journal article

Chadeau-Hyam M, Wang H, Eales O, Haw D, Bodinier B, Whitaker M, Walters CE, Ainslie KEC, Atchison C, Fronterre C, Diggle PJ, Page AJ, Trotter AJ, Ashby D, Barclay W, Taylor G, Cooke G, Ward H, Darzi A, Riley S, Donnelly CA, Elliott Pet al., 2022, SARS-CoV-2 infection and vaccine effectiveness in England (REACT-1): a series of cross-sectional random community surveys, The Lancet Respiratory Medicine, Vol: 10, Pages: 355-366, ISSN: 2213-2600

SummaryBackground England has experienced a third wave of the COVID-19 epidemic since the end of May, 2021, coincidingwith the rapid spread of the delta (B.1.617.2) variant, despite high levels of vaccination among adults. Vaccinationrates (single dose) in England are lower among children aged 16–17 years and 12–15 years, whose vaccination inEngland commenced in August and September, 2021, respectively. We aimed to analyse the underlying dynamicsdriving patterns in SARS-CoV-2 prevalence during September, 2021, in England.Methods The REal-time Assessment of Community Transmission-1 (REACT-1) study, which commenced datacollection in May, 2020, involves a series of random cross-sectional surveys in the general population of Englandaged 5 years and older. Using RT-PCR swab positivity data from 100 527 participants with valid throat and noseswabs in round 14 of REACT-1 (Sept 9–27, 2021), we estimated community-based prevalence of SARS-CoV-2 andvaccine effectiveness against infection by combining round 14 data with data from round 13 (June 24 to July 12, 2021;n=172 862).Findings During September, 2021, we estimated a mean RT-PCR positivity rate of 0·83% (95% CrI 0·76–0·89), with areproduction number (R) overall of 1·03 (95% CrI 0·94–1·14). Among the 475 (62·2%) of 764 sequenced positiveswabs, all were of the delta variant; 22 (4·63%; 95% CI 3·07–6·91) included the Tyr145His mutation in the spikeprotein associated with the AY.4 sublineage, and there was one Glu484Lys mutation. Age, region, key worker status,and household size jointly contributed to the risk of swab positivity. The highest weighted prevalence was observedamong children aged 5–12 years, at 2·32% (95% CrI 1·96–2·73) and those aged 13–17 years, at 2·55% (2·11–3·08).The SARS-CoV-2 epidemic grew in those aged 5–11 years, with an R of 1&m

Journal article

Eales O, Ainslie KEC, Walters CE, Wang H, Atchison C, Ashby D, Donnelly CA, Cooke G, Barclay W, Ward H, Darzi A, Elliott P, Riley Set al., 2022, Appropriately smoothing prevalence data to inform estimates of growth rate and reproduction number

<jats:title>Abstract</jats:title><jats:p>The time-varying reproduction number (<jats:bold><jats:italic>R</jats:italic></jats:bold><jats:sub><jats:bold><jats:italic>t</jats:italic></jats:bold></jats:sub>) can change rapidly over the course of a pandemic due to changing restrictions, behaviours, and levels of population immunity. Many methods exist that allow the estimation of <jats:bold><jats:italic>R</jats:italic></jats:bold><jats:sub><jats:bold><jats:italic>t</jats:italic></jats:bold></jats:sub> from case data. However, these are not easily adapted to point prevalence data nor can they infer <jats:bold><jats:italic>R</jats:italic></jats:bold><jats:sub><jats:bold><jats:italic>t</jats:italic></jats:bold></jats:sub> across periods of missing data. We developed a Bayesian P-spline model suitable for fitting to a wide range of epidemic time-series, including point-prevalence data. We demonstrate the utility of the model by fitting to periodic daily SARS-CoV-2 swab-positivity data in England from the first 7 rounds (May 2020 – December 2020) of the REal-time Assessment of Community Transmission-1 (REACT-1) study. Estimates of <jats:bold><jats:italic>R</jats:italic></jats:bold><jats:sub><jats:bold><jats:italic>t</jats:italic></jats:bold></jats:sub> over the period of two subsequent rounds (6-8 weeks) and single rounds (2-3 weeks) inferred using the Bayesian P-spline model were broadly consistent with estimates from a simple exponential model, with overlapping credible intervals. However, there were sometimes substantial differences in point estimates. The Bayesian P-spline model was further able to infer changes in <jats:bold><jats:italic>R</jats:italic></jats:bold><jats:sub><jats

Journal article

Eales O, Page AJ, de Oliveira Martins L, Wang H, Bodinier B, Haw D, Jonnerby J, Atchison C, Ashby D, Barclay W, Taylor G, Cooke G, Ward H, Darzi A, Riley S, Chadeau-Hyam M, Donnelly CA, Elliott Pet al., 2021, SARS-CoV-2 lineage dynamics in England from September to November 2021: high diversity of Delta sub-lineages and increased transmissibility of AY.4.2

<jats:title>Abstract</jats:title><jats:p>Since the emergence of SARS-CoV-2, evolutionary pressure has driven large increases in the transmissibility of the virus. However, with increasing levels of immunity through vaccination and natural infection the evolutionary pressure will switch towards immune escape. Here we present phylogenetic relationships and lineage dynamics within England (a country with high levels of immunity), as inferred from a random community sample of individuals who provided a self-administered throat and nose swab for rt-PCR testing as part of the REal-time Assessment of Community Transmission-1 (REACT-1) study. From 9 to 27 September 2021 (round 14) and 19 October to 5 November 2021 (round 15), all lineages sequenced within REACT-1 were Delta or a Delta sub-lineage with 44 unique lineages identified. The proportion of the original Delta variant (B.1.617.2) was found to be increasing between September and November 2021, which may reflect an increasing number of sub-lineages which have yet to be identified. The proportion of B.1.617.2 was greatest in London, which was further identified as a region with an increased level of genetic diversity. The Delta sub-lineage AY.4.2 was found to be robustly increasing in proportion, with a reproduction number 15% (8%, 23%) greater than its parent and most prevalent lineage, AY.4. Both AY.4.2 and AY.4 were found to be geographically clustered in September but this was no longer the case by late October/early November, with only the lineage AY.6 exhibiting clustering towards the South of England. Though no difference in the viral load based on cycle threshold (Ct) values was identified, a lower proportion of those infected with AY.4.2 had symptoms for which testing is usually recommend (loss or change of sense of taste, loss or change of sense of smell, new persistent cough, fever), compared to AY.4 (p = 0.026). The evolutionary rate of SARS-CoV-2, as measured by the mutation rate, was fou

Journal article

Elliott P, Haw D, Wang H, Eales O, Walters C, Ainslie K, Atchison C, Fronterre C, Diggle P, Page A, Trotter A, Prosolek S, The COVID-19 Genomics UK Consortium COG-UK, Ashby D, Donnelly C, Barclay W, Taylor G, Cooke G, Ward H, Darzi A, Riley Set al., 2021, Exponential growth, high prevalence of SARS-CoV-2 and vaccine effectiveness associated with Delta variant, Science, Vol: 374, Pages: 1-11, ISSN: 0036-8075

SARS-CoV-2 infections were rising during early summer 2021 in many countries associated with the Delta variant. We assessed RT-PCR swab-positivity in the REal-time Assessment of Community Transmission-1 (REACT-1) study in England. We observed sustained exponential growth with average doubling time (June-July 2021) of 25 days driven by complete replacement of Alpha variant by Delta, and by high prevalence at younger less-vaccinated ages. Unvaccinated people were three times more likely than double-vaccinated people to test positive. However, after adjusting for age and other variables, vaccine effectiveness for double-vaccinated people was estimated at between ~50% and ~60% during this period in England. Increased social mixing in the presence of Delta had the potential to generate sustained growth in infections, even at high levels of vaccination.

Journal article

Pollett S, Johansson MA, Reich NG, Brett-Major D, Del Valle SY, Venkatramanan S, Lowe R, Porco T, Berry IM, Deshpande A, Kraemer MUG, Blazes DL, Pan-ngum W, Vespigiani A, Mate SE, Silal SP, Kandula S, Sippy R, Quandelacy TM, Morgan JJ, Ball J, Morton LC, Althouse BM, Pavlin J, van Panhuis W, Riley S, Biggerstaff M, Viboud C, Brady O, Rivers Cet al., 2021, Recommended reporting items for epidemic forecasting and prediction research: The EPIFORGE 2020 guidelines, PLOS MEDICINE, Vol: 18, ISSN: 1549-1277

Journal article

Elliott J, Whitaker M, Bodinier B, Eales O, Riley S, Ward H, Cooke G, Darzi A, Chadeau M, Elliott Pet al., 2021, Predictive symptoms for COVID-19 in the community: REACT-1 study of over one million people, PLoS Medicine, Vol: 18, Pages: 1-14, ISSN: 1549-1277

Background:Rapid detection, isolation and contact tracing of community COVID-19 cases are essential measures to limit the community spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We aimed to identify a parsimonious set of symptoms that jointly predict COVID-19 and whether predictive symptoms differ between B.1.1.7 (Alpha) lineage (predominating as of April 2021in the USA, UK and elsewhere) and wild type.Methods and Findings:We obtained throat and nose swabs with valid SARS-CoV-2 polymerase chain reaction (PCR) test results from 1,147,370 volunteers aged 5 years and above (6,450 positives) in the REal-time Assessment of Community Transmission-1 (REACT-1) study. This involved repeated community-based random surveys of prevalence in England (study rounds 2 to 8, June 2020 to January 2021, response rates 22%-27%). Participants were asked about symptoms occurring in the week prior to testing. Viral genome sequencing was carried out for PCR positive samples with N-gene cycle threshold value < 34 (N = 1,079) in round 8 (January 2021). In univariate analysis, all 26 surveyed symptoms were associated with PCR positivity compared with non-symptomatic people. Stability selection (1,000 penalized logistic regression models with 50% subsampling) among people reporting at least one symptom identified seven symptoms as jointly and positively predictive of PCR positivity in rounds 2–7 (June to December 2020): loss or change of sense of smell, loss or change of sense of taste, fever, new persistent cough, chills, appetite loss and muscle aches. The resulting model (rounds 2–7) predicted PCR positivity in round 8 with area under the curve (AUC) of 0.77. The same seven symptoms were selected as jointly predictive of B.1.1.7 infection in round 8, although comparing B.1.1.7 with wild type, new persistent cough and sore throat were more predictive of B.1.1.7 infection while loss or change of sense of smell was more predictive of the wild type. Main

Journal article

Eales O, Walters C, Wang H, Haw D, Ainslie K, Atchison C, Page A, Prosolek S, Trotter A, Viet TL, Alikhan N-F, Jackson LM, Ludden C, COG UK TCGUKC, Ashby D, Donnelly C, Cooke G, Barclay W, Ward H, Darzi A, Elliott P, Riley Set al., 2021, Characterising the persistence of RT-PCR positivity and incidence in a community survey of SARS-CoV-2

BackgroundCommunity surveys of SARS-CoV-2 RT-PCR swab-positivity provide prevalence estimates largely unaffected by biases from who presents for routine case testing. The REal-time Assessment of Community Transmission-1 (REACT-1) has estimated swab-positivity approximately monthly since May 2020 in England from RT-PCR testing of self-administeredthroat and nose swabs in random non-overlapping cross-sectional community samples. Estimating infection incidence from swab-positivity requires an understanding of the persistence of RT-PCR swab positivity in the community.MethodsDuring round 8 of REACT-1 from 6 January to 22 January 2021, of the 2,282 participants who tested RT-PCR positive, we recruited 896 (39%) from whom we collected up to two additional swabs for RT-PCR approximately 6 and 9 days after the initial swab. We estimated sensitivity and duration of positivity using an exponential model of positivity decay, for all participants and for subsets by initial N-gene cycle threshold (Ct) value, symptom status, lineage and age. Estimates of infection incidence were obtained for the entire duration of the REACT-1 study using P-splines.ResultsWe estimated the overall sensitivity of REACT-1 to detect virus on a single swab as 0.79 (0.77, 0.81) and median duration of positivity following a positive test as 9.7 (8.9, 10.6) days. We found greater median duration of positivity where there was a low N-gene Ct value, in those exhibiting symptoms, or for infection with the Alpha variant. The estimated proportionof positive individuals detected on first swab, was found to be higher 𝑃 for those with an 0 initially low N-gene Ct value and those who were pre-symptomatic. When compared to swab-positivity, estimates of infection incidence over the duration of REACT-1 included sharper features with evident transient increases around the time of key changes in socialdistancing measures.DiscussionHome self-swabbing for RT-PCR based on a single swab, as implemented in REACT-1, has hig

Working paper

Ward H, Atchison C, Whitaker M, Donnelly CA, Riley S, Ashby D, Darzi A, Barclay WS, Cooke G, Elliott Pet al., 2021, Increasing SARS-CoV-2 antibody prevalence in England at the start of the second wave: REACT-2 Round 4 cross-sectional study in 160,000 adults

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>REACT-2 Study 5 is a population survey of the prevalence of SARS-CoV-2 antibodies in the community in England.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We contacted a random sample of the population by sending a letter to named individuals aged 18 or over from the NHS GP registrations list. We then sent respondents a lateral flow immunoassay (LFIA) kit for SARS-CoV-2 antibody self-testing and asked them to perform the test at home and complete a questionnaire, including reporting of their test result. Overall, 161,537 adults completed questionnaires and self-administered LFIA tests for IgG against SARS-CoV-2 between 27 October and 10 November 2020.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>The overall adjusted and weighted prevalence was 5.6% (95% CI 5.4-5.7). This was an increase from 4.4% (4.3-4.5) in round 3 (September), a relative increase of 26.9% (24.0-29.9).The largest increase by age was in the 18 to 24 year old age group, which increased (adjusted and weighted) from 6.7% (6.3-7.2) to 9.9% (9.3-10.4), and in students, (adjusted, unweighted) from 5.9% (4.8-7.1) to 12.1% (10.8-13.5). Prevalence increased most in Yorkshire and The Humber, from 3.4% (3.0-3.8) to 6.3% (5.9-6.8) and the North West from 4.5% (4.2-4.9) to 7.7% (7.2-8.1). In contrast, the prevalence in London was stable, at 9.5% (9.0-9.9) and 9.5% (9.1-10.0) in rounds 3 and 4 respectively. We found the highest prevalence in people of Bangladeshi 15.1% (10.9-20.5), Pakistani 13.9% (11.2-17.2) and African 13.5% (10.7-16.8) ethnicity, and lowest in those of white British ethnicity at 4.2% (4.0-4.3).</jats:p></jats:sec><jats:sec><jats:title>Interpretation</jats:title><jats:p>The second wave of infection in England is apparen

Journal article

Ward H, Whitaker M, Tang SN, Atchison C, Darzi A, Donnelly C, Diggle P, Ashby D, Riley S, Barclay W, Elliott P, Cooke Get al., 2021, Vaccine uptake and SARS-CoV-2 antibody prevalence among 207,337 adults during May 2021 in England: REACT-2 study

Background The programme to vaccinate adults in England has been rapidly implementedsince it began in December 2020. The community prevalence of SARS-CoV-2 anti-spikeprotein antibodies provides an estimate of total cumulative response to natural infection andvaccination. We describe the distribution of SARS-CoV-2 IgG antibodies in adults inEngland in May 2021 at a time when approximately 7 in 10 adults had received at least onedose of vaccine.Methods Sixth round of REACT-2 (REal-time Assessment of Community Transmission-2),a cross-sectional random community survey of adults in England, from 12 to 25 May 2021;207,337 participants completed questionnaires and self-administered a lateral flowimmunoassay test producing a positive or negative result.Results Vaccine coverage with one or more doses, weighted to the adult population inEngland, was 72.9% (95% confidence interval 72.7-73.0), varying by age from 25.1% (24.5-25.6) of those aged 18 to 24 years, to 99.2% (99.1-99.3) of those 75 years and older. Inadjusted models, odds of vaccination were lower in men (odds ratio [OR] 0.89 [0.85-0.94])than women, and in people of Black (0.41 [0.34-0.49]) compared to white ethnicity. Therewas higher vaccine coverage in the least deprived and highest income households. Peoplewho reported a history of COVID-19 were less likely to be vaccinated (OR 0.61 [0.55-0.67]).There was high coverage among health workers (OR 9.84 [8.79-11.02] and care workers (OR4.17 [3.20-5.43]) compared to non-key workers, but lower in hospitality and retail workers(OR 0.73 [0.64-0.82] and 0.77 [0.70-0.85] respectively) after adjusting for age and keycovariates.

Working paper

Riley S, Eales O, Haw D, Wang H, Walters C, Ainslie K, Christina A, Fronterre C, Diggle P, Ashby D, Donnelly C, Barclay W, Cooke G, Ward H, Darzi A, Elliott Pet al., 2021, REACT-1 round 13 interim report: acceleration of SARS-CoV-2 Delta epidemic in the community in England during late June and early July 2021

BackgroundDespite high levels of vaccination in the adult population, cases of COVID-19 have risenexponentially in England since the start of May 2021 driven by the Delta variant. However,with far fewer hospitalisations and deaths per case during the recent growth in casescompared with 2020, it is intended that all remaining social distancing legislation in Englandwill be removed from 19 July 2021.MethodsWe report interim results from round 13 of the REal-time Assessment of CommunityTransmission-1 (REACT-1) study in which a cross-sectional sample of the population ofEngland was asked to provide a throat and nose swab for RT-PCR and to answer aquestionnaire. Data collection for this report (round 13 interim) was from 24 June to 5 July2021.ResultsIn round 13 interim, we found 237 positives from 47,729 swabs giving a weighted prevalenceof 0.59% (0.51%, 0.68%) which was approximately four-fold higher compared with round 12at 0.15% (0.12%, 0.18%). This resulted from continued exponential growth in prevalencewith an average doubling time of 15 (13, 17) days between round 12 and round 13.However, during the recent period of round 13 interim only, we observed a shorter doublingtime of 6.1 (4.0, 12) days with a corresponding R number of 1.87 (1.40, 2.45). There weresubstantial increases in all age groups under the age of 75 years, and especially at youngerages, with the highest prevalence in 13 to 17 year olds at 1.33% (0.97%, 1.82%) and in 18 to24 years olds at 1.40% (0.89%, 2.18%). Infections have increased in all regions with thelargest increase in London where prevalence increased more than eight-fold from 0.13%(0.08%, 0.20%) in round 12 to 1.08% (0.79%, 1.47%) in round 13 interim. Overall,prevalence was over 3 times higher in the unvaccinated compared with those reporting twodoses of vaccine in both round 12 and round 13 interim, although there was a similarproportional increase in prevalence in vaccinated and unvaccinated individuals between thetwo rounds.DiscussionWe

Working paper

Gaythorpe K, Bhatia S, Mangal T, Unwin H, Imai N, Cuomo-Dannenburg G, Walters C, Jauneikaite E, Bayley H, Kont M, Mousa A, Whittles L, Riley S, Ferguson Net al., 2021, Children’s role in the COVID-19 pandemic: a systematic review of early surveillance data on susceptibility, severity, and transmissibility, Scientific Reports, Vol: 11, Pages: 1-14, ISSN: 2045-2322

Background: SARS-CoV-2 infections have been reported in all age groups including infants, children, and adolescents. However, the role of children in the COVID-19 pandemic is still uncertain. This systematic review of early studies synthesises evidence on the susceptibility of children to SARS-CoV-2 infection, the severity and clinical outcomes in children with SARS-CoV-2 infection, and the transmissibility of SARS-CoV-2 by children in the early phases of the COVID-19 pandemic. Methods and findings: A systematic literature review was conducted in PubMed. Reviewers extracted data from relevant, peer-reviewed studies published up to July 4th 2020 during the first wave of the SARS-CoV-2 outbreak using a standardised form and assessed quality using the NIH Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. For studies included in the meta-analysis, we used a random effects model to calculate pooled estimates of the proportion of children considered asymptomatic or in a severe or critical state. We identified 2,775 potential studies of which 128 studies met our inclusion criteria; data were extracted from 99, which were then quality assessed. Finally, 29 studies were considered for the meta-analysis that included information of symptoms and/or severity, these were further assessed based on patient recruitment. Our pooled estimate of the proportion of test positive children who were asymptomatic was 21.1% (95% CI: 14.0 - 28.1%), based on 13 included studies, and the proportion of children with severe or critical symptoms was 3.8% (95% CI: 1.5 - 6.0%), based on 14 included studies. We did not identify any studies designed to assess transmissibility in children and found that susceptibility to infection in children was highly variable across studies.Conclusions: Children’s susceptibility to infection and onward transmissibility relative to adults is still unclear and varied widely between studies. However, it is evident that most children e

Journal article

Turtle J, Riley P, Ben-Nun M, Riley Set al., 2021, Accurate influenza forecasts using type-specific incidence data for small geographic units, PLOS COMPUTATIONAL BIOLOGY, Vol: 17, ISSN: 1553-734X

Journal article

Whitaker M, Elliott J, Chadeau-Hyam M, Riley S, Darzi A, Cooke G, Ward H, Elliott Pet al., 2021, Persistent symptoms following SARS-CoV-2 infection in a random community sample of 508,707 people

IntroductionLong COVID, describing the long-term sequelae after SARS-CoV-2 infection, remains a poorlydefined syndrome. There is uncertainty about its predisposing factors and the extent of theresultant public health burden, with estimates of prevalence and duration varying widely.MethodsWithin rounds 3–5 of the REACT-2 study, 508,707 people in the community in England wereasked about a prior history of COVID-19 and the presence and duration of 29 differentsymptoms. We used uni- and multivariable models to identify predictors of persistence ofsymptoms (12 weeks or more). We estimated the prevalence of symptom persistence at 12weeks, and used unsupervised learning to cluster individuals by symptoms experienced.ResultsAmong the 508,707 participants, the weighted prevalence of self-reported COVID-19 was 19.2%(95% CI: 19.1,19.3). 37.7% of 76,155 symptomatic people post COVID-19 experienced at leastone symptom, while 14.8% experienced three or more symptoms, lasting 12 weeks or more. Thisgives a weighted population prevalence of persistent symptoms of 5.75% (5.68, 5.81) for one and2.22% (2.1, 2.26) for three or more symptoms. Almost a third of people 8,771/28,713 (30.5%)with at least one symptom lasting 12 weeks or more reported having had severe COVID-19symptoms (“significant effect on my daily life”) at the time of their illness, giving a weightedprevalence overall for this group of 1.72% (1.69,1.76). The prevalence of persistent symptomswas higher in women than men (OR: 1.51 [1.46,1.55]) and, conditional on reporting symptoms,risk of persistent symptoms increased linearly with age by 3.5 percentage points per decade oflife. Obesity, smoking or vaping, hospitalisation , and deprivation were also associated with ahigher probability of persistent symptoms, while Asian ethnicity was associated with a lowerprobability. Two stable clusters were identified based on symptoms that persisted for 12 weeks ormore: in the largest cluster, tiredness predominated

Working paper

Kiti MC, Aguolu OG, Liu CY, Mesa AR, Regina R, Woody M, Willebrand K, Couzens C, Bartelsmeyer T, Nelson KN, Jenness S, Riley S, Melegaro A, Ahmed F, Malik F, Lopman BA, Omer SBet al., 2021, Social contact patterns among employees in 3 US companies during early phases of the COVID-19 pandemic, April to June 2020, EPIDEMICS, Vol: 36, ISSN: 1755-4365

Journal article

Riley S, Wang H, Eales O, Haw D, Walters C, Ainslie K, Atchison C, Fronterre C, Diggle P, Page A, Prosolek S, Trotter AJ, Le Viet T, Alikhan N-F, The COVID-19 Genomics UK Consortium COG-UK, Ashby D, Donnelly C, Cooke G, Barclay W, Ward H, Darzi A, Elliott Pet al., 2021, REACT-1 round 12 report: resurgence of SARS-CoV-2 infections in England associated with increased frequency of the Delta variant

BackgroundEngland entered a third national lockdown from 6 January 2021 due to the COVID-19pandemic. Despite a successful vaccine rollout during the first half of 2021, cases andhospitalisations have started to increase since the end of May as the SARS-CoV-2 Delta(B.1.617.2) variant increases in frequency. The final step of relaxation of COVID-19restrictions in England has been delayed from 21 June to 19 July 2021.MethodsThe REal-time Assessment of Community Transmision-1 (REACT-1) study measures theprevalence of swab-positivity among random samples of the population of England. Round12 of REACT-1 obtained self-administered swab collections from participants from 20 May2021 to 7 June 2021; results are compared with those for round 11, in which swabs werecollected from 15 April to 3 May 2021.ResultsBetween rounds 11 and 12, national prevalence increased from 0.10% (0.08%, 0.13%) to0.15% (0.12%, 0.18%). During round 12, we detected exponential growth with a doublingtime of 11 (7.1, 23) days and an R number of 1.44 (1.20, 1.73). The highest prevalence wasfound in the North West at 0.26% (0.16%, 0.41%) compared to 0.05% (0.02%, 0.12%) in theSouth West. In the North West, the locations of positive samples suggested a cluster inGreater Manchester and the east Lancashire area. Prevalence in those aged 5-49 was 2.5times higher at 0.20% (0.16%, 0.26%) compared with those aged 50 years and above at0.08% (0.06%, 0.11%). At the beginning of February 2021, the link between infection ratesand hospitalisations and deaths started to weaken, although in late April 2021, infectionrates and hospital admissions started to reconverge. When split by age, the weakened linkbetween infection rates and hospitalisations at ages 65 years and above was maintained,while the trends converged below the age of 65 years. The majority of the infections in theyounger group occurred in the unvaccinated population or those without a stated vaccinehistory. We observed the rapid replacement of the Alpha (

Working paper

Riley S, Ainslie KEC, Eales O, Walters CE, Wang H, Atchison C, Fronterre C, Diggle PJ, Ashby D, Donnelly CA, Cooke G, Barclay W, Ward H, Darzi A, Elliott Pet al., 2021, Resurgence of SARS-CoV-2: detection by community viral surveillance, Science, Vol: 372, Pages: 990-995, ISSN: 0036-8075

Surveillance of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has mainly relied on case reporting, which is biased by health service performance, test availability, and test-seeking behaviors. We report a community-wide national representative surveillance program in England based on self-administered swab results from ~594,000 individuals tested for SARS-CoV-2, regardless of symptoms, between May and the beginning of September 2020. The epidemic declined between May and July 2020 but then increased gradually from mid-August, accelerating into early September 2020 at the start of the second wave. When compared with cases detected through routine surveillance, we report here a longer period of decline and a younger age distribution. Representative community sampling for SARS-CoV-2 can substantially improve situational awareness and feed into the public health response even at low prevalence.

Journal article

Ward H, Cooke GS, Atchison C, Whitaker M, Elliott J, Moshe M, Brown JC, Flower B, Daunt A, Ainslie K, Ashby D, Donnelly CA, Riley S, Darzi A, Barclay W, Elliott Pet al., 2021, Prevalence of antibody positivity to SARS-CoV-2 following the first peak of infection in England: Serial cross-sectional studies of 365,000 adults, The Lancet Regional Health - Europe, Vol: 4, Pages: 1-7, ISSN: 2666-7762

BackgroundThe time-concentrated nature of the first wave of the COVID-19 epidemic in England in March and April 2020 provides a natural experiment to measure changes in antibody positivity at the population level before onset of the second wave and initiation of the vaccination programme.MethodsThree cross-sectional national surveys with non-overlapping random samples of the population in England undertaken between late June and September 2020 (REACT-2 study). 365,104 adults completed questionnaires and self-administered lateral flow immunoassay (LFIA) tests for IgG against SARS-CoV-2.FindingsOverall, 17,576 people had detectable antibodies, a prevalence of 4.9% (95% confidence intervals 4.9, 5.0) when adjusted for test characteristics and weighted to the adult population of England. The prevalence declined from 6.0% (5.8, 6.1), to 4.8% (4.7, 5.0) and 4.4% (4.3, 4.5), over the three rounds of the study a difference of -26.5% (-29.0, -23.8). The highest prevalence and smallest overall decline in positivity was in the youngest age group (18-24 years) at -14.9% (-21.6, -8.1), and lowest prevalence and largest decline in the oldest group (>74 years) at -39.0% (-50.8, -27.2). The decline from June to September 2020 was largest in those who did not report a history of COVID-19 at -64.0% (-75.6, -52.3), compared to -22.3% (-27.0, -17.7) in those with SARS-CoV-2 infection confirmed on PCR.InterpretationA large proportion of the population remained susceptible to SARS-CoV-2 infection in England based on naturally acquired immunity from the first wave. Widespread vaccination is needed to confer immunity and control the epidemic at population level.FundingThis work was funded by the Department of Health and Social Care in England.

Journal article

Kwok KO, Wei WI, Huang Y, Kam KM, Chan EYY, Riley S, Chan HHH, Hui DSC, Wong SYS, Yeoh EKet al., 2021, Evolving Epidemiological Characteristics of COVID-19 in Hong Kong From January to August 2020: Retrospective Study, JOURNAL OF MEDICAL INTERNET RESEARCH, Vol: 23, ISSN: 1438-8871

Journal article

Riley S, Eales O, Haw D, Walters C, Wang H, Ainslie K, Atchison C, Fronterre C, Diggle P, Ashby D, Donnelly C, Cooke G, Barclay W, Ward H, Darzi A, Elliott Pet al., 2021, REACT-1 round 10 report: Level prevalence of SARS-CoV-2 swab-positivity in England during third national lockdown in March 2021

BackgroundIn England, hospitalisations and deaths due to SARS-CoV-2 have been falling consistentlysince January 2021 during the third national lockdown of the COVID-19 pandemic. The firstsignificant relaxation of that lockdown occurred on 8 March when schools reopened.MethodsThe REal-time Assessment of Community Transmission-1 (REACT-1) study augmentsroutine surveillance data for England by measuring swab-positivity for SARS-CoV-2 in thecommunity. The current round, round 10, collected swabs from 11 to 30 March 2021 and iscompared here to round 9, in which swabs were collected from 4 to 23 February 2021.ResultsDuring round 10, we estimated an R number of 1.00 (95% confidence interval 0.81, 1.21).Between rounds 9 and 10 we estimated national prevalence has dropped by ~60% from0.49% (0.44%, 0.55%) in February to 0.20% (0.17%, 0.23%) in March. There weresubstantial falls in weighted regional prevalence: in South East from 0.36% (0.29%, 0.44%)in round 9 to 0.07% (0.04%, 0.12%) in round 10; London from 0.60% (0.48%, 0.76%) to0.16% (0.10%, 0.26%); East of England from 0.47% (0.36%, 0.60%) to 0.15% (0.10%,0.24%); East Midlands from 0.59% (0.45%, 0.77%) to 0.19% (0.13%, 0.28%); and NorthWest from 0.69% (0.54%, 0.88%) to 0.31% (0.21%, 0.45%). Areas of apparent higherprevalence remain in parts of the North West, and Yorkshire and The Humber. The highestprevalence in March was found among school-aged children 5 to 12 years at 0.41% (0.27%,0.62%), compared with the lowest in those aged 65 to 74 and 75 and over at 0.09% (0.05%,0.16%). The close approximation between prevalence of infections and deaths (suitablylagged) is diverging, suggesting that infections may have resulted in fewer hospitalisationsand deaths since the start of widespread vaccination.ConclusionWe report a sharp decline in prevalence of infections between February and March 2021.We did not observe an increase in the prevalence of SARS-CoV-2 following the reopening ofschools in England, although the decline of p

Working paper

Riley S, Wang H, Eales O, Haw D, Walters C, Ainslie K, Atchison C, Fronterre C, Diggle P, Ashby D, Donnelly C, Cooke G, Barclay W, Ward H, Darzi A, Elliott Pet al., 2021, REACT-1 round 9 final report: Continued but slowing decline of prevalence of SARS-CoV-2 during national lockdown in England in February 2021

BackgroundEngland will start to exit its third national lockdown in response to the COVID-19 pandemicon 8th March 2021, with safe effective vaccines being rolled out rapidly against abackground of emerging transmissible and immunologically novel variants of SARS-CoV-2.A subsequent increase in community prevalence of infection could delay further relaxation oflockdown if vaccine uptake and efficacy are not sufficiently high to prevent increasedpressure on healthcare services.MethodsThe PCR self-swab arm of the REal-time Assessment of Community Transmission Study(REACT-1) estimates community prevalence of SARS-CoV-2 infection in England based onrandom cross-sections of the population ages five and over. Here, we present results fromthe complete round 9 of REACT-1 comprising round 9a in which swabs were collected from4th to 12th February 2021 and round 9b from 13th to 23rd February 2021. We also comparethe results of REACT-1 round 9 to round 8, in which swabs were collected mainly from 6thJanuary to 22nd January 2021.ResultsOut of 165,456 results for round 9 overall, 689 were positive. Overall weighted prevalence ofinfection in the community in England was 0.49% (0.44%, 0.55%), representing a fall of overone third from round 8. However the rate of decline of the epidemic has slowed from 15 (13,17) days, estimated for the period from the end of round 8 to the start of round 9, to 31 daysestimated using data from round 9 alone (lower confidence limit 17 days). When comparinground 9a to 9b there were apparent falls in four regions, no apparent change in one regionand apparent rises in four regions, including London where there was a suggestion ofsub-regional heterogeneity in growth and decline. Smoothed prevalence maps suggest largecontiguous areas of growth and decline that do not align with administrative regions.Prevalence fell by 50% or more across all age groups in round 9 compared to round 8, withprevalence (round 9) ranging from 0.21% in those aged 65 and over to 0

Working paper

Moshe M, Daunt A, Flower B, Simmons B, Brown JC, Frise R, Penn R, Kugathasan R, Petersen C, Stockmann H, Ashby D, Riley S, Atchison C, Taylor GP, Satkunarajah S, Naar L, Klaber R, Badhan A, Rosadas C, Marchesin F, Fernandez N, Sureda-Vives M, Cheeseman H, O'Hara J, Shattock R, Fontana G, Pallett SJC, Rayment M, Jones R, Moore LSP, Ashrafian H, Cherapanov P, Tedder R, McClure M, Ward H, Darzi A, Cooke GS, Barclay WS, On behalf of the REACT Study teamet al., 2021, SARS-CoV-2 lateral flow assays for possible use in national covid-19 seroprevalence surveys (REACT2): diagnostic accuracy study, BMJ: British Medical Journal, Vol: 372, Pages: 1-8, ISSN: 0959-535X

Objective: To evaluate the performance of new lateral flow immunoassays (LFIAs) suitable for use in a national COVID-19 seroprevalence programme (REACT2).Design: Laboratory sensitivity and specificity analyses were performed for seven LFIAs on a minimum of 200 sera from individuals with confirmed SARS-CoV-2 infection, and 500 pre-pandemic sera respectively. Three LFIAs were found to have a laboratory sensitivity superior to the finger-prick sensitivity of the LFIA currently used in REACT2 seroprevalence studies (84%). These LFIAs were then further evaluated through finger-prick testing on participants with confirmed previous SARS-CoV-2 infection. Two LFIAs (Surescreen, Panbio) were evaluated in clinics in June-July, 2020, and a third LFIA (AbC-19) in September, 2020. A Spike protein enzyme-linked immunoassay (S-ELISA) and hybrid double antigen binding assay (DABA) were used as laboratory reference standards.Setting: Laboratory analyses were performed at Imperial College, London and University facilities in London, UK. Research clinics for finger-prick sampling were run in two affiliated NHS trusts.Participants: Sensitivity analysis on sera were performed on 320 stored samples from previous participants in the REACT2 programme with confirmed previous SARS-CoV-2 infection. Specificity analysis was performed using 1000 pre-pandemic sera. 100 new participants with confirmed previous SARS-CoV-2 infection attended study clinics for finger-prick testing.Main outcome measures: The accuracy of LFIAs in detecting IgG antibodies to SARS-CoV-2 in comparison to two in-house ELISAs.Results: The sensitivity of seven new LFIAs using sera varied between 69% and 100% (vs S-ELISA/hybrid DABA). Specificity using sera varied between 99.6% and 100%. Sensitivity on finger-prick testing for Panbio, Surescreen and AbC-19 was 77% (CI 61.4 to 88.2), 86% (CI 72.7 to 94.8) and 69% (CI 53.8 to 81.3) respectively vs S-ELISA/hybrid DABA. Sensitivity for sera from matched clinical samples performe

Journal article

Ward H, Cooke G, Whitaker M, Redd R, Eales O, Brown J, Collet K, Cooper E, Daunt A, Jones K, Moshe M, Willicombe M, Day S, Atchison C, Darzi A, Donnelly C, Riley S, Ashby D, Barclay W, Elliott Pet al., 2021, REACT-2 Round 5: increasing prevalence of SARS-CoV-2 antibodies demonstrate impact of the second wave and of vaccine roll-out in England

BackgroundEngland has experienced high rates of SARS-CoV-2 infection during the COVID-19 pandemic, affecting in particular minority ethnic groups and more deprived communities. A vaccination programme began in England in December 2020, with priority given to administering thefirst dose to the largest number of older individuals, healthcare and care home workers.MethodsA cross-sectional community survey in England undertaken between 26 January and 8 February 2021 as the fifth round of the REal-time Assessment of Community Transmission-2 (REACT-2) programme. Participants completed questionnaires, including demographic details and clinical and COVID-19 vaccination histories, and self-administered a lateral flowimmunoassay (LFIA) test to detect IgG against SARS-CoV-2 spike protein. There were sufficient numbers of participants to analyse antibody positivity after 21 days from vaccination with the PfizerBioNTech but not the AstraZeneca/Oxford vaccine which was introduced slightly later.ResultsThe survey comprised 172,099 people, with valid IgG antibody results from 155,172. The overall prevalence of antibodies (weighted to be representative of the population of England and adjusted for test sensitivity and specificity) in England was 13.9% (95% CI 13.7, 14.1) overall, 37.9% (37.2, 38.7) in vaccinated and 9.8% (9.6, 10.0) in unvaccinated people.The prevalence of antibodies (weighted) in unvaccinated people was highest in London at 16.9% (16.3, 17.5), and higher in people of Black (22.4%, 20.8, 24.1) and Asian (20.0%, 19.0, 21.0) ethnicity compared to white (8.5%, 8.3, 8.7) people. The uptake of vaccination by age was highest in those aged 80 years or older (93.5%). Vaccine confidence was high with 92.0% (91.9, 92.1) of people saying that they had accepted or intended to accept the offer.Vaccine confidence varied by age and ethnicity, with lower confidence in young people and those of Black ethnicity. Particular concerns were identified around pregnancy, fertility and alle

Working paper

Riley S, Walters C, Wang H, Eales O, Haw D, Ainslie K, Atchison C, Fronterre C, Diggle P, Ashby D, Donnelly C, Cooke G, Barclay W, Ward H, Darzi A, Elliott Pet al., 2021, REACT-1 round 9 interim report: downward trend of SARS-CoV-2 in England in February 2021 but still at high prevalence

Background and Methods: England entered its third national lockdown of the COVID-19pandemic on 6th January 2021 with the aim of reducing the daily number of deaths andpressure on healthcare services. The real-time assessment of community transmission study(REACT-1) obtains throat and nose swabs from randomly selected people in England inorder to describe patterns of SARS-CoV-2 prevalence. Here, we report data from round 9aof REACT-1 for swabs collected between 4th and 13th February 2021.Results: Out of 85,473 tested-swabs, 378 were positive. Overall weighted prevalence ofinfection in the community in England was 0.51%, a fall of more than two thirds since our lastreport (round 8) in January 2021 when 1.57% of people tested positive. We estimate ahalving time of 14.6 days and a reproduction number R of 0.72, based on the difference inprevalence between the end of round 8 and the beginning of round 9. Although prevalencefell in all nine regions of England over the same period, there was greater uncertainty in thetrend for North West, North East, and Yorkshire and The Humber. Prevalence fellsubstantially across all age groups with highest prevalence among 18- to 24-year olds at0.89% (0.47%, 1.67%) and those aged 5 to12 years at 0.86% (0.60%, 1.24%). Largehousehold size, living in a deprived neighbourhood, and Asian ethnicity were all associatedwith increased prevalence. Healthcare and care home workers were more likely to testpositive compared to other workers.Conclusions: There is a strong decline in prevalence of SARS-CoV-2 in England among thegeneral population five to six weeks into lockdown, but prevalence remains high: at levelssimilar to those observed in late September 2020. Also, the number of COVID-19 cases inhospitals is higher than at the peak of the first wave in April 2020. The effects of easing ofsocial distancing when we transition out of lockdown need to be closely monitored to avoid aresurgence in infections and renewed pressure on health services.

Working paper

Nouvellet P, Bhatia S, Cori A, Ainslie K, Baguelin M, Bhatt S, Boonyasiri A, Brazeau N, Cattarino L, Cooper L, Coupland H, Cucunuba Perez Z, Cuomo-Dannenburg G, Dighe A, Djaafara A, Dorigatti I, Eales O, van Elsland S, NASCIMENTO F, Fitzjohn R, Gaythorpe K, Geidelberg L, green W, Hamlet A, Hauck K, Hinsley W, Imai N, Jeffrey, Jeffrey B, Knock E, Laydon D, Lees J, Mangal T, Mellan T, Nedjati Gilani G, Parag K, Pons Salort M, Ragonnet-Cronin M, Riley S, Unwin H, Verity R, Vollmer M, Volz E, Walker P, Walters C, Wang H, Watson O, Whittaker C, Whittles L, Xi X, Ferguson N, Donnelly Cet al., 2021, Reduction in mobility and COVID-19 transmission, Nature Communications, Vol: 12, ISSN: 2041-1723

In response to the COVID-19 pandemic, countries have sought to control SARS-CoV-2 transmission by restricting population movement through social distancing interventions, thus reducing the number of contacts.Mobility data represent an important proxy measure of social distancing, and here, we characterise the relationship between transmission and mobility for 52 countries around the world.Transmission significantly decreased with the initial reduction in mobility in 73% of the countries analysed, but we found evidence of decoupling of transmission and mobility following the relaxation of strict control measures for 80% of countries. For the majority of countries, mobility explained a substantial proportion of the variation in transmissibility (median adjusted R-squared: 48%, interquartile range - IQR - across countries [27-77%]). Where a change in the relationship occurred, predictive ability decreased after the relaxation; from a median adjusted R-squared of 74% (IQR across countries [49-91%]) pre-relaxation, to a median adjusted R-squared of 30% (IQR across countries [12-48%]) post-relaxation.In countries with a clear relationship between mobility and transmission both before and after strict control measures were relaxed, mobility was associated with lower transmission rates after control measures were relaxed indicating that the beneficial effects of ongoing social distancing behaviours were substantial.

Journal article

Colizza V, Grill E, Mikolajczyk R, Cattuto C, Kucharski A, Riley S, Kendall M, Lythgoe K, Bonsall D, Wymant C, Abeler-Dorner L, Ferretti L, Fraser Cet al., 2021, Time to evaluate COVID-19 contact-tracing apps, NATURE MEDICINE, Vol: 27, Pages: 361-362, ISSN: 1078-8956

Journal article

Elliott J, Whitaker M, Bodinier B, Riley S, Ward H, Cooke G, Darzi A, Chadeau-Hyam M, Elliott P, Elliott J, Whitaker M, Bodinier B, Riley S, Ward H, Cooke G, Darzi A, Chadeau-Hyam M, Elliott Pet al., 2021, Symptom reporting in over 1 million people: community detection of COVID-19

Control of the SARS-CoV-2 epidemic requires rapid identification and isolation of infectedindividuals and their contacts. Community testing in England (Pillar 2) by polymerase chainreaction (PCR) is reserved for those reporting at least one of four ‘classic’ COVID-19 symptoms(loss or change of sense of smell, loss or change of sense of taste, fever, new continuous cough). 1Detection of positive cases in the community might be improved by including additionalsymptoms and their combinations. We used data from the REal-time Assessment of CommunityTransmission-1 (REACT-1) study to investigate symptom profiles for PCR positivity at differentages. Among rounds 2–7 (June to December 2020), an age-stratified, variable selection approachstably selected chills (all ages), headache (5–17 years), appetite loss (18–54 and 55+ years) andmuscle aches (18–54 years) as jointly and positively predictive of PCR positivity together withthe classic four symptoms. Between round 7 (November to December 2020) and round 8(January 2021) when new variant B.1.1.7 predominated, only loss or change of sense of smell(more predictive in round 7) and (borderline) new persistent cough (more predictive in round 8)differed between cases. At any level of PCR testing, triage based on the symptoms identifiedhere would result in more cases detected than the current approach .

Working paper

Ward H, Atchison C, Whitaker M, Ainslie KEC, Elliott J, Okell L, Redd R, Ashby D, Donnelly C, Barclay W, Darzi A, Cooke G, Riley S, Elliott Pet al., 2021, SARS-CoV-2 antibody prevalence in England following the first peak of the pandemic., Nature Communications, Vol: 12, Pages: 1-8, ISSN: 2041-1723

England has experienced a large outbreak of SARS-CoV-2, disproportionately affecting people from disadvantaged and ethnic minority communities. It is unclear how much of this excess is due to differences in exposure associated with structural inequalities. Here we report from the REal-time Assessment of Community Transmission-2 (REACT-2) national study of over 100,000 people. After adjusting for test characteristics and re-weighting to the population, overall antibody prevalence is 6.0% (95% CI: 5.8-6.1). An estimated 3.4 million people had developed antibodies to SARS-CoV-2 by mid-July 2020. Prevalence is two- to three-fold higher among health and care workers compared with non-essential workers, and in people of Black or South Asian than white ethnicity, while age- and sex-specific infection fatality ratios are similar across ethnicities. Our results indicate that higher hospitalisation and mortality from COVID-19 in minority ethnic groups may reflect higher rates of infection rather than differential experience of disease or care.

Journal article

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