Estimates of the rate of infection and asymptomatic COVID-19 disease in a population sample from SE England

Wells, Philippa M.; Doores, Katie J.; Couvreur, Simon; Nunez, Rocio Martinez; Seow, Jeffrey; Graham, Carl; Acors, Sam; Kouphou, Neophytos; Neil, Stuart J.D.; Tedder, Richard S.; Matos, Pedro M.; Poulton, Kate; Lista, Maria Jose; Dickenson, Ruth E.; Sertkaya, Helin; Maguire, Thomas J.A.; Scourfield, Edward J.; Bowyer, Ruth C.E.; Hart, Deborah; O'Bryne, Aoife; Steel, Kathyrn J.A.; Hemmings, Oliver; Rosadas, Carolina; McClure, Myra O.; Capedevilla-pujol, Joan; Wolf, Jonathan; Ourselin, Sebastien; Brown, Matthew A.; Malim, Michael H.; Spector, Tim; Steves, Claire J.

BACKGROUND: Understanding of the true asymptomatic rate of infection of SARS-CoV-2 is currently limited, as is understanding of the population-based seroprevalence after the first wave of COVID-19 within the UK. The majority of data thus far come from hospitalised patients, with little focus on general population cases, or their symptoms. METHODS: We undertook enzyme linked immunosorbent assay characterisation of IgM and IgG responses against SARS-CoV-2 spike glycoprotein and nucleocapsid protein of 431 unselected general-population participants of the TwinsUK cohort from South-East England, aged 19-86 (median age 48; 85% female). 382 participants completed prospective logging of 14 COVID-19 related symptoms via the COVID Symptom Study App, allowing consideration of serology alongside individual symptoms, and a predictive algorithm for estimated COVID-19 previously modelled on PCR positive individuals from a dataset of over 2 million. FINDINGS: We demonstrated a seroprevalence of 12% (51participants of 431). Of 48 seropositive individuals with full symptom data, nine (19%) were fully asymptomatic, and 16 (27%) were asymptomatic for core COVID-19 symptoms: fever, cough or anosmia. Specificity of anosmia for seropositivity was 95%, compared to 88% for fever cough and anosmia combined. 34 individuals in the cohort were predicted to be Covid-19 positive using the App algorithm, and of those, 18 (52%) were seropositive. INTERPRETATION: Seroprevalence amongst adults from London and South-East England was 12%, and 19% of seropositive individuals with prospective symptom logging were fully asymptomatic throughout the study. Anosmia demonstrated the highest symptom specificity for SARS-CoV-2 antibody response. FUNDING: NIHR BRC, CDRF, ZOE global LTD, RST-UKRI/MRC