Cohort profile: characterisation, determinants, mechanisms and consequences of the long-term effects of COVID-19 - providing the evidence base for health care services (CONVALESCENCE) in the UK.

Purpose: The pathogenesis of the long-lasting symptoms which can follow an infection with the SARS-CoV-2 virus ('long covid') is not fully understood. The 'COroNaVirus post-Acute Long-term EffectS: Constructing an evidENCE base' (CONVALESCENCE) study was established as part of the Longitudinal Health and Wellbeing COVID-19 UK National Core Study. We performed a deep phenotyping case-control study nested within two cohorts (the Avon Longitudinal Study of Parents and Children and TwinsUK) as part of CONVALESCENCE.

Participants: From September 2021 to May 2023, 349 participants attended the CONVALESCENCE deep phenotyping clinic at University College London. Four categories of participants were recruited: cases of long covid ()/)), alongside three control groups: those with neither long covid symptoms nor evidence of prior COVID-19 ()/ those who self-reported COVID-19 and had evidence of SARS-CoV-2 infection, but did not report long covid () and those who self-reported persistent symptoms attributable to COVID-19 but no evidence of SARS-CoV-2 infection (). Remote wearable measurements were performed up until February 2024.

Findings To Date: This cohort profile describes the baseline characteristics of the CONVALESCENCE cohort. Of the 349 participants, 141 (53±15 years old; 21 (15%) men) were cases, 89 (55±16 years old; 11 (12%) men) were in control group 1, 75 (49±15 years old; 25 (33%) men) were in control group 2 and 44 (55±16 years old; 9 (21%) men) were in control group 3.

Future Plans: The study aims to use a multiorgan score calculated as the cumulative total for each of nine domains (ie, lung, vascular, heart, kidney, brain, autonomic function, muscle strength, exercise capacity and physical performance). The availability of data preceding acute COVID-19 infection in cohorts may help identify the consequences of infection independent of pre-existing subclinical disease and also provide evidence of determinants that influence the development of long covid.