Modeling Exit Strategies from COVID-19 Lockdown with a Focus on Antibody Tests

Reinhard German; Anatoli Djanatliev; Lisa Maile; Peter Bazan; Holger Hackstein

Currently, an increasing variety of SARS-COV-2 antibody tests is available. From a medical point of view, seroconversion, i.e., positivity of IgM/IgG antibodies can be detected as early as 7-14 days after symptomatic COVID-19 infection [3] . However, since many patients can still shed oral infectious virus up to 22 days after onset of symptoms or after first positive COVID-19 PCR test result [3] , sole positivity of combined IgM/IgG is not a good indicator for non-infectious individuals and herd immunity. In this respect, isolated detection of virus-specific IgG should be preferred, because it has a delayed kinetic in comparison to IgM. Furthermore, with respect to disease modeling and contagiousness a safety buffer of 14 days added on the date of IgG positivity may be reasonable in order to define a reliable time-point when a person should be considered recovered and non-infectious. Another important variable of antibody tests is their specificity and sensitivity. For the reliable calculation of herd immunity a high specificity of an antibody test is critical and should be >99%. Also, an extremely high sensitivity of the antibody test might be desirable and nice to have. However, it is not of critical importance, as it can be assumed that most people with a functioning herd immunity also have sufficiently high antibody levels.