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BACKGROUNDTo fight severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), mass vaccination has begun in many countries. To investigate the usefulness of a serological assay to predict vaccine efficacy, we analyzed the levels of IgG, IgM, and IgA against the receptor binding domain (RBD) of SARS-CoV-2 in the sera from BNT162b2 vaccinated individuals in Japan. METHODSThis study included 219 individuals who received two doses of BNT162b2. The levels of IgG, IgM, and IgA against RBD were measured by enzyme-linked immunosorbent assay before and after the first and second vaccination, respectively. The relationship between antibody levels and several factors including age, gender, and hypertension were analyzed. Virus-neutralizing activity in sera was measured to determine the correlation with the levels of antibodies. A chemiluminescent enzyme immunoassay (CLEIA) method to measure IgG against RBD was developed and validated for the clinical setting. RESULTSThe levels of all antibody isotypes were increased after vaccination. Among them, RBD-IgG was dramatically increased after the second vaccination. The IgG levels in females were significantly higher than in males. There was a negative correlation between age and IgG levels in males. The IgG levels significantly correlated with the neutralizing activity. The CLEIA assay measuring IgG against RBD showed a reliable performance and a high correlation with neutralizing activity. CONCLUSIONSMonitoring of IgG against RBD is a powerful tool to predict the efficacy of SARS-CoV-2 vaccination and provides useful information in considering a personalized vaccination strategy for COVID-19.
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Serological tests for detection of anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies in blood are expected to identify individuals who have acquired immunity against SARS-CoV-2 and indication of seroprevalence of SARS-CoV-2 infection. Many serological tests have been developed to detect antibodies against SARS-CoV-2. However, these tests have considerable variations in their specificity and sensitivity, and whether they can predict levels of neutralizing activity is yet to be determined. This study aimed to investigate the kinetics and neutralizing activity of various antigen-specific antibody isotypes against SARS-CoV-2 in serum of coronavirus disease 2019 (COVID-19) patients confirmed via polymerase chain reaction test. We developed IgG, IgM and IgA measurement assays for each antigen, including receptor-binding domain (RBD) of spike (S) protein, S1 domain, full length S protein, S trimer and nucleocapsid (N) domain, based on enzyme-linked immunosorbent assay. The assays of the S protein for all isotypes showed high specificity, while the assays for all isotypes against N protein showed lower specificity. The sensitivity of all antigen-specific antibody isotypes depended on the timing of the serum collection and all of them, except for IgM against N protein, reached more than 90% at 15-21 days post-symptom onset. The best correlation with virus neutralizing activity was found for IgG against RBD (RBD-IgG), and levels of RBD-IgG in sera from four severe COVID-19 patients increased concordantly with neutralizing activity. Our results provide valuable information regarding the selection of serological test for seroprevalence and vaccine evaluation studies.
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BackgroundSeveral immunochromatographic serological test kits have been developed to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific antibodies, but their relative performance and potential clinical utility is unclear. MethodsThree commercially available serological test kits were evaluated using 99 serum samples collected from 29 patients diagnosed with coronavirus disease 2019 (COVID-19). ResultsThe IgM antibody-positive rates of the three serological test kits for samples taken at the early stage of the disease (0-6 days after onset) were 19.0%, 23.8%, and 19.0%, respectively. The IgM antibody-positive rates over the entire period were 21.2%, 60.6%, and 15.2%, respectively. The IgG antibody-positive rates for samples taken after 13 days of onset were 100.0%, 97.6%, and 97.6%, respectively. ConclusionThere were large differences among the results of the three test kits. Only few cases showed positive results for IgM in the early stage of disease and the IgM antibody-positive rates over the entire period were low, suggesting that the kits used in this study were unsuitable for diagnosis of COVID-19. The IgG antibody was positive in almost all samples after 13 days of onset, suggesting that it may be useful for determining infections in the recent past.
