When users signed up on the app, it collected data on sex, age and ethnicity (Asian, Black, Chinese, Middle Eastern, mixed or white); core health risk factors, including height, weight and common disease status (e.g. cancer, diabetes, and heart, kidney and lung disease); the use of medications (e.g. corticosteroids, immunosuppressants and blood pressure medications); and whether the user is a health care worker.
Participants were also asked if they’d had a COVID-19 test, what kind they had and what the result was. Users could update their status daily and record up to 14 symptoms: abdominal pain, chest pain, delirium, diarrhoea, fatigue, fever, headache, hoarse voice, anosmia, persistent cough, shortness of breath, skipped meals, sore throat and unusual muscle pains. Starting in April 2020, two rashes were also added: raised, red, itchy welts on the face or body, or sudden swelling of the face or lips (body rash); and red/purple sores or blisters on the feet or toes (acral rash).