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For the control of immunity in COVID-19 survivors and vaccinated subjects there is an urgent need for reliable and rapid serological assays.Based on samples from 63 COVID-19 survivors up to seven months after symptom onset, and on 50 serum samples taken before the beginning of the pandemic, we compared the performance of three commercial immunoassays for the detection of SARS-CoV-2 IgA and IgG antibodies (Euroimmun SARS-COV-2 IgA/IgG, Mikrogen recomWell SARS-CoV-2 IgA/IgG, and SERION ELISA agile SARS-CoV-2 IgA/IgG) and three rapid lateral flow (immunochromatographic) tests (Abbott Panbio COVID-19 IgG/IgM, NADAL COVID-19 IgG/IgM, and Cleartest Corona 2019-nCOV IgG/IgM) with a plaque-reduction neutralization test (PRNT50) representing the gold standard. In addition, we report and validate a novel, non-commercial flow cytometry bead-based surrogate test.57 out of 63 PCR-confirmed COVID-19 patients (90 %) showed neutralizing antibodies. The sensitivity of the seven assays ranged from 7.0 % to 98.3 %, the specificity from 86.0 % to 100.00 %. Only one commercial immunoassay showed a sensitivity and specificity of greater than 98 %. These data indicate abundant interassay variability.

Haemophilus influenzae can cause respiratory and invasive infections ([1][1]), whereas H. haemolyticus (Hh) is generally considered apathogenic ([2][2]) and is rarely associated with disease ([3][3]). Since both species colonize the upper respiratory tract, their distinction is crucial in routine