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

Jablonka, A.; Happle, C.; Cossmann, A.; Strankov, M. V.; Zychlinsky Scharff, A.; Ernst, D.; Behrens, G. M.

Objectives: Healthcare professionals (HCP) are at the frontline of the coronavirus disease 2019 (COVID-19) crisis. Serological screening is used to identify severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) prevalence, but many questions regarding infection risk and utility of serological testing amongst HCP remain unanswered. To improve this, we initiated the COVID-19 Contact (CoCo) study. Design and setting: The CoCo study is an ongoing, prospective, longitudinal, observational study at Hannover Medical School, a large university hospital in Northern Germany and affili-ated care providers. Since March 2020, it monitors anti-SARS-CoV-2 immune responses and collects information on symptoms of infection, work, home and self-perceived infection risk. Participants: More than 1250 male and female HCP are enrolled. Inclusion criteria are (1) working as HCP in clinical care at our university, affiliated hospitals or private practices, (2) written informed consent, (3) age >18 years. Exclusion criteria are (1) refusal to give informed consent, (2) contraindication to venepuncture. Sampling/Intervention: Study participants provide samples weekly to six-monthly (7.5 ml serum and 7.5 ml EDTA blood) and fill out a questionnaire. 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 test. Individual results are made available for each participant online via a dedicated study website. This study also compares different serological testing assays and explores further humoral and cellular immune markers. Study protocols are continually adapted to the evolving situation of the pandemic. Conclusions: This ongoing prospective study aims to answer central questions on the prev-alence and kinetics of anti-SARS-CoV-2-humoral immune responses and validity of serologi-cal testing of HCP in a region with comparably high healthcare standards and low COVID-19 prevalence. Therefore, our results may be relevant to other regions around the world in man-aging this unprecedented situation.