BACKGROUND. In the COVID-19 pandemic, highly selective serological testing is essential to define exposure to SARS-CoV-2 virus. Many tests have been developed, yet with variable speed to first result, and of unknown quality, particularly when considering the prediction of neutralizing capacity. OBJECTIVES/METHODS. The LIAISON® SARS-CoV-2 S1/S2 IgG assay was designed to measure antibodies against the SARS-CoV-2 native S1/S2 proteins in a standardized automated chemiluminescent assay. Clinical and analytical performance of the test were validated in an observational study using residual samples (>1500) with positive or negative COVID-19 diagnosis. RESULTS. The LIAISON® SARS-CoV-2 S1/S2 IgG assay proved to be highly selective and specific, and offers semiquantitative measures of serum or plasma levels of anti-S1/S2 IgG with neutralizing activity. The assay's diagnostic sensitivity was 91.3% and 95.7% at >5 or ≥15 days from diagnosis, respectively, and 100% when assessed against a neutralizing assay. The assay's specificity ranged between 97% and 98.5%. The average imprecision of the assay was <5 % coefficient of variation. Assay performance at 2 different cut-offs was evaluated to optimize predictive values. CONCLUSIONS. The automated LIAISON® SARS-CoV-2 S1/S2 IgG assay brings efficient, sensitive, specific, and precise serological testing to the laboratory, with the capacity to test large amounts of samples per day: first results are available within 35 minutes with a throughput of 170 tests/hour. The semiquantitative results provided by the test also associate with the presence of neutralizing antibodies, and may provide a useful tool for the large scale screening of convalescent plasma for safe therapeutic use.

word count: 246 20 Text word count: 3188 21 22 4 ABSTRACT 23BACKGROUND. In the Covid-19 pandemic, highly selective serological testing is 24 essential to define exposure to SARS-CoV-2 virus. Many tests have been developed, 25 yet with variable speed to first result, and of unknown quality, particularly when 26 considering the prediction of neutralizing capacity. 27 OBJECTIVES/METHODS. The LIAISON ® SARS-CoV-2 S1/S2 IgG assay was designed 28 to measure antibodies against the SARS-CoV-2 native S1/S2 proteins in a standardized 29 automated chemiluminescent assay. Clinical and analytical performance of the test 30 were validated in an observational study using residual samples (>1500) with positive or 31 negative Covid-19 diagnosis. 32RESULTS. The LIAISON ® SARS-CoV-2 S1/S2 IgG assay proved highly selective and 33 specific, and offers semiquantitative measures of serum or plasma levels of anti-S1/S2 34 IgG with neutralizing activity. The diagnostic sensitivity was 91.3% and 95.7% at >5 or 35 ≥15 days from diagnosis respectively, and 100% when assessed against a neutralizing 36 assay. The specificity ranged between 97% and 98.5%. The average imprecision of the 37 assay was <5 % coefficient of variation. Assay performance at 2 different cut-offs was 38 evaluated to optimize predictive values in settings with different % disease prevalence. 39 CONCLUSIONS. The automated LIAISON ® SARS-CoV-2 S1/S2 IgG assay brings 40 efficient, sensitive, specific, and precise serological testing to the laboratory, with the 41 capacity to test large amounts of samples per day: first results are available within 35 42 minutes with a throughput of 170 tests/hour. The test also provides a semiquantitative 43 measure to identify samples with neutralizing antibodies, useful also for a large scale 44 screening of convalescent plasma for safe therapeutic use. 45 5 IMPORTANCE 46With the worldwide advance of the COVID-19 pandemic, efficient, reliable and 47 accessible diagnostic tools are needed to support public health officials and healthcare 48 providers in their efforts to deliver optimal medical care, and articulate sound 49 demographic policy. DiaSorin has developed an automated serology based assay for 50 the measurement of IgG specific to SARS CoV-2 Spike protein, and tested its clinical 51 performance in collaboration with Italian health care professionals who provided access 52 to large numbers of samples from infected and non-infected individuals. The assay 53 delivers excellent sensitivity and specificity, and is able to identify samples with high 54 levels of neutralizing antibodies. This will provide guidance in assessing the true 55 immune status of subjects, as well as meeting the pressing need to screen donors for 56 high titer convalescent sera for subsequent therapeutic and prophylactic use. 57 58 SARS-CoV-2, the virus responsible for the Covid-19 pandemic, has spread at an 59 alarming rate since the first case tracked back to mid-November of 2019 in Wuhan 60 China (1). Contraction and subsequent transmission accrue...

SARS-CoV-2 vaccination has proven effective in inducing an immune response in healthy individuals and is progressively us allowing to overcome the pandemic. Recent evidence has shown that response to vaccination in some vulnerable patients may be diminished, and it has been proposed a booster dose. We tested the kinetic of development of serum antibodies to the SARS-CoV-2 Spike protein, their neutralizing capacity, the CD4 and CD8 IFN-γ T-cell response in 328 subjects, including 131 immunocompromised individuals (cancer, rheumatologic, and hemodialysis patients), 160 health-care workers (HCW) and 37 subjects older than 75 yr, after vaccination with two or three doses of mRNA vaccines. We stratified the patients according to the type of treatment. We found that immunocompromised patients, depending on the type of treatment, poorly respond to SARS-CoV-2 mRNA vaccines. However, an additional booster dose of vaccine induced a good immune response in almost all of the patients except those receiving anti-CD20 antibody. Similarly to HCW, previously infected and vaccinated immunocompromised individuals demonstrate a stronger SARS-CoV-2–specific immune response than those who are vaccinated without prior infection.

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The Authors studied the immune responses of 691 health care workers who were given HEVAC B vaccine (455 subjects) and HB Vax vaccine (216 subjects). The immune responses were correlated with data obtained by questionnaires: age, sex, B.M.I., drinking habits, smoking. The results showed correlation between these variables and immune response to vaccine.