Modelling repurposed from pandemic influenza is currently informing all strategies forSARS-CoV-2 and the disease COVID-19. A customized disease specific understanding will beimportant to understand subsequent disease waves, vaccine development and therapeutics.For this reason, ISARIC (the International Severe Acute Respiratory and EmergingInfection Consortium) was set up in advance. This focuses on hospitalised andconvalescent serum samples to understand severe illness and associated immune response.However, many subjects are seroconverting with mild or even subclinical disease.Information is needed about subclinical infection, the significance of baseline immunestatus and the earliest immune changes that may occur in mild disease to compare withthose of SARS-CoV-2. There is also a need to understand the vulnerability and response toCOVID-19 of the NHS workforce of healthcare workers (HCWs). HCW present a cohort withlikely higher exposure and seroconversion rates than the general population, but who canbe followed up with potential for serial testing enabling an insight into early diseaseand markers of risk for disease severity. We have set up "COVID-19: Healthcare workerBioresource: Immune Protection and Pathogenesis in SARS-CoV-2". This urgent fieldworkaims to secure significant (n=400) sampling of healthcare workers (demographics, swabs,blood sampling) at baseline, and weekly whilst they are well and attending work, withacute sampling (if hospitalised, via ISARIC, if their admission hospital is part of theISARIC network) and convalescent samples post illness. These will be used to addressspecific questions around the impact of baseline immune function, the earliest immuneresponses to infection, and the biology of those who get non-hospitalized disease forlocal research and as a national resource. The proposal links directly with other ongoingISARIC and community COVID projects sampling in children and the older age population.Reasonable estimates suggest the usable window for baseline sampling of NHS HCW isclosing fast (e.g. baseline sampling within 3 weeks).