The case reports mentioned above point out the potential of serological assays to add to the diagnosis of COVID-19. So far, a large number of serological assays have been developed in response to the diagnostic need [14]. Data on the validation and comparison of the performance of these assays are emerging but are still limited [15–18]. Since antibody production by the specific immune system is subject to delay, a lower diagnostic performance of serological assays in the early phase of the disease is expected. So far, studies have revealed that antibodies could be detected as early as 3–6 days after symptom onset [9,10,19,20].