Antibody titers and neutralizing activity in cases of COVID-19 after a single dose of vaccination

Vaccines for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have shown high efficacy in preventing the onset of disease. However, the immune response to infection immediately after the first vaccination remains unknown. We examined the anti-SARS-CoV-2-binding-antibody titers and neutralizing activity in patients who developed coronavirus disease 2019 after the first vaccination. The amount of anti-SARS-CoV-2-binding antibodies and neutralizing activity drastically increased from the first to the second collection. Our results may provide important data on the course of immune response following vaccination.

Incomplete humoral response including neutralizing antibodies in asymptomatic to mild COVID-19 patients in Japan

The pandemic of COVID-19 is still ongoing, and many studies on serum antibodies have been reported, however, there are few studies about asymptomatic and mild patients. In this study, we enrolled 44 COVID-19 patients with relatively mild disease and 48 pre-pandemic controls. We measured serum antibodies against extracellular domain, S1 domain, and receptor-binding domain of Spike and N protein, examined neutralization titers by authentic virus neutralization assay and newly-developed bead/cell-based Spike-ACE2 inhibition assay, and compared them with clinical features. Most of these antibodies, including neutralizing titers, were mutually correlated, and the production of antibodies were associated with low Ct values of PCR test, disease severity, symptoms especially pneumonia, lymphopenia, and serological test including CRP, LD, D-dimer, and procalcitonin. Notably, 87.5% of asymptomatic and 23.5% of mild patients did not have antibody against SARS-CoV-2. Our results revealed the inadequate acquisition of humoral immunity in patients with asymptomatic and mild COVID-19 patients.

Impact of complement and difference of cell-based assay and ELISA in determination of neutralization capacity against mumps and measles virus

Neutralizing antibodies against mumps and measles virus are considered a correlate of protection against these diseases. Measurement of neutralizing antibodies is mostly performed using plaque reduction neutralization assay or 50% cell culture infective dose (CCID₅₀) neutralization assay, but there are attempts for measuring neutralizing antibodies using enzyme-linked immunosorbent assay (ELISA) which is simpler, but the literature data regarding its convenience are diverse. The role of complement and antibodies in neutralizing capacity of sera is not completely defined. Here, CCID₅₀ neutralization assay and ELISA were used to determine the neutralization capacity against mumps and measles virus in human sera and therapeutic immunoglobulins (IVIGs). Results showed no correlation of neutralization titers obtained by CCID₅₀ neutralization assay and IgG content obtained by ELISA for mumps or measles in human sera. Data showed some neutralization activity against measles virus and quite high against mumps virus of naïve guinea pig serum and that its addition increases neutralization capacity of IVIG and human sera against mumps and measles viruses. Heat inactivation of human sera reduced neutralization capacity against measles to small extent, and substantially against mumps virus. There is a significant impact of complement in measurement of neutralization capacity against mumps virus.