Protocol for longitudinal assessment of SARS-CoV-2-specific immune responses in healthcare professionals in Hannover, Germany: the prospective, longitudinal, observational COVID-19 Contact (CoCo) study

Background During the current pandemic, healthcare professionals (HCP) have been at the frontline of the crisis. Serological screening may help in identifying severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) prevalence. However, given the rapidly evolving situation in spring 2020, many questions regarding coronavirus disease 2019 (COVID-19) infection risk and utility of serological testing remained unanswered. To address these questions, we initiated the COVID-19 Contact (CoCo) study at Hannover Medical School, a large university hospital in Northern Germany and affiliated care providers. Methods The CoCo study is an ongoing, prospective, longitudinal, observational study in HCP and individuals with potential contact to SARS-CoV-2. It monitors anti-SARS-CoV-2 immunoglobulin serum levels and collects information on symptoms of respiratory infection, work and home environment, and self-perceived SARS-CoV-2 infection risk. Inclusion criteria are (1) working as HCP in clinical care at our university centre, affiliated hospitals or private practices, (2) written informed consent and (3) age >18 years. Exclusion criteria are (1) refusal to give informed consent and (2) contraindication to venepuncture. Study participants are asked to provide weekly to six-monthly samples (7.5 ml serum and 7.5 ml EDTA blood) and fill out a questionnaire. Since March 2020, around 1250 HCP have been included in the study. At each study visit, sera are screened for anti-SARS-CoV-2 spike protein 1 (S1) immunoglobulin G (IgG) by enzyme-linked immunosorbent assay (ELISA). Positive or borderline positive samples are re-assessed with an alternative serological test. Individual results for each study participant are made available online via a dedicated study website. This study also aims to compare different serological testing assays, as well as explore further humoral and cellular immune markers. Study protocols are continually adapted to the rapidly evolving situation of the current pandemic. Discussion This ongoing prospective study will aim to answer central questions on the prevalence and kinetics of anti-SARS-CoV-2-humoral immune responses and the validity of serological testing of HCP in a region with high healthcare standard and comparatively low COVID-19 prevalence. As such, our results are highly relevant to other regions and may support HCP around the world in managing this unprecedented situation. Trial registration German Clinical Trial Registry, DRKS00021152. Registered 4th April 2020 -retrospectively registered, https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00021152 Protocol summary