Two SARS-CoV-2 IgG immunoassays comparison and time-course profile of antibodies response

OUP accepted manuscript

Objective

To examine the immunoglobulin G-receptor-binding domain (IgG-RBD) response and changes in fibrinogen and D-dimer concentrations in individuals with a past coronavirus infection and followed by CoronaVac.

Methods

The study consisted of a total of 116 participants. Blood samples were drawn from subjects 21–25 days after they received first and second doses of CoronaVac as well as from individuals with a past infection. Fibrinogen, D-dimer, and IgG-RBD concentrations were measured.

Results

The IgG concentrations of the vaccinated subjects were significantly higher (P < .001), fibrinogen levels were lower (P < .001), and D-dimer levels increased following the second vaccination compared with the first vaccination (P = .083). No difference was obtained in IgG-RBD between vaccinated and previously infected individuals (P = .063). The differences in fibrinogen and D-dimer were statistically nonsignificant between both groups.

Conclusion

The CoronaVac vaccine appears to be safe and effective. It is essential for individuals to take personal protective measures, such as using masks and distancing.

Antibodies against SARS-CoV-2 Time Course in Patients and Vaccinated Subjects: An Evaluation of the Harmonization of Two Different Methods

The time course of antibodies against SARS-CoV-2 is not yet well elucidated, especially in people who underwent a vaccination campaign. In this study, we measured the antibodies anti-S1 and anti-RBD with two different methods, both in patients and in vaccinated subjects. One hundred and eight specimens from 48 patients with COVID-19 (time from the onset of symptoms from 3 to 368 days) and 60 specimens from 20 vaccinated subjects (collected after 14 days from the first dose, 14 days and 3 months after a second dose of Comirnaty) were evaluated. We used an ELISA method that measured IgG against anti-Spike 1, and a chemiluminescence immunoassay that measured IgG anti-RBD. In the patients, the antibodies concentrations tended to decline after a few months, with both the methods, but they persisted relatively high up to nearly a year after the symptoms. In the vaccinated subjects, the antibodies were already detectable after the first dose, but after the booster, they showed a significant increase. However, the decrease was rapid, given that 3 months after the second vaccination, they were reduced to less than a quarter. The conversion of the results into BAU units improves the relationship between the two methods. However, in the vaccinated subjects, there was no evidence of proportional error after the conversion, while in the patients, the difference between the two methods remained significant.

Quantitative SARS-CoV-2 Spike Antibody Response in COVID-19 Patients Using Three Fully Automated Immunoassays and a Surrogate Virus Neutralization Test

Quantitative SARS-CoV-2 antibody assays against the spike (S) protein are useful for monitoring immune response after infection or vaccination. We compared the results of three chemiluminescent immunoassays (CLIAs) (Abbott, Roche, Siemens) and a surrogate virus neutralization test (sVNT, GenScript) using 191 sequential samples from 32 COVID-19 patients. All assays detected >90% of samples collected 14 days after symptom onset (Abbott 97.4%, Roche 96.2%, Siemens 92.3%, and GenScript 96.2%), and overall agreement among the four assays was 91.1% to 96.3%. When we assessed time-course antibody levels, the Abbott and Siemens assays showed higher levels in patients with severe disease (p < 0.05). Antibody levels from the three CLIAs were correlated (r = 0.763–0.885). However, Passing–Bablok regression analysis showed significant proportional differences between assays and converting results to binding antibody units (BAU)/mL still showed substantial bias. CLIAs had good performance in predicting sVNT positivity (Area Under the Curve (AUC), 0.959–0.987), with Abbott having the highest AUC value (p < 0.05). SARS-CoV-2 S protein antibody levels as assessed by the CLIAs were not interchangeable, but showed reliable performance for predicting sVNT results. Further standardization and harmonization of immunoassays might be helpful in monitoring immune status after COVID-19 infection or vaccination.

Persistence of humoral response upon SARS-CoV-2 infection

SARS‐CoV‐2 continues to leave its toll on global health and the economy. Management of the pandemic will rely heavily on the degree of adaptive immunity persistence following natural SARS‐CoV‐2 infection. Along with the progression of the pandemic, more literature on the persistence of the SARS‐CoV‐2‐specific antibody response is becoming available. Here, we summarize findings on the persistence of the humoral, including neutralizing antibody, response at three to eight months post SARS‐CoV‐2 infection in non‐pregnant adults. While the comparability of the literature is limited, findings on the detectability of immunoglobulin G class of antibodies (IgG) were most consistent and were reported in most studies to last for six to eight months. Studies investigating the response of immunoglobins M and A (IgM, IgA) were limited and reported mixed results, in particular, for IgM. The majority of studies observed neutralizing antibodies at all time points tested, which in some studies lasted up to eight months. The presence of neutralizing antibodies has been linked to protection from re‐infection, suggesting long‐term immunity to SARS‐CoV‐2. These neutralizing capacities may be challenged by emerging virus variants, but mucosal antibodies as well as memory B and T cells may optimize future immune responses. Thus, further longitudinal investigation of PCR‐confirmed seropositive individuals using sensitive assays is warranted to elucidate the nature and duration of a more long‐term humoral response.

Evaluation of the performance of SARS--CoV--2 antibody assays for a longitudinal population-based study of COVID--19 spread in St. Petersburg, Russia

Geographical variation in severe acute respiratory syndrome coronavirus 2 (SARS­‐CoV­‐2) spread requires seroprevalence studies based on local tests, but robust validation is needed. We summarize an evaluation of antibody tests used in a serological study of SARS‐­CoV­‐2 in Saint Petersburg, Russia. We validated three different antibody assays: chemiluminescent microparticle immunoassay (CMIA) Abbott Architect SARS‐­CoV­‐2 immunoglobulin G (IgG), enzyme­ linked immunosorbent assay (ELISA) CoronaPass total antibodies test, and ELISA SARS­‐CoV‐­2‐­IgG‐­EIA‐­BEST. Clinical sensitivity was estimated with the SARS­‐CoV­‐2 polymerase chain reaction (PCR) test as the gold standard using manufacturer recommended cutoff. Specificity was estimated using pre­pandemic sera samples. The median time between positive PCR test results and antibody tests was 21 weeks. Measures of concordance were calculated against the microneutralization test (MNA).Sensitivity was equal to 91.1% (95% confidence intervbal [CI]: 78.8–97.5), 90% (95% CI: 76.4–96.4), and 63.1% (95% CI [50.2–74.7]) for ELISA Coronapass, ELISA Vector­Best, and CMIA Abbott, respectively. Specificity was equal to 100% for all the tests. Comparison of receiver operating characteristics has shown lower AUC for CMIA Abbott. The cut­off SC/O ratio of 0.28 for CMIA Abbott resulted in a sensitivity of 80% at the same level of specificity. Less than 33% of the participants with positive antibody test results had neutralizing antibodies in titers 1:80 and above. Antibody assays results and MNA correlated moderately. This study encourages the use of local antibody tests and sets the reference for seroprevalence correction. Available tests' sensitivity allows detecting antibodies within the majority of PCR­ positive individuals. The Abbott assay sensitivity can be improved by incorporating a new cut­off. Manufacturers' test characteristics may introduce bias into the study results.

1)

This report is the first diagnostic performance study of antibody assays used in the representative population‐based serological study of SARS‐CoV‐2 in St. Petersburg, Russia.

2)

The sensitivity for two local assays was equal to 91.1% (95%CI: 78.8‐97.5) and 89.1\% (95%CI: 76.4‐96.4), CMIA Abbott's sensitivity was equal to 63.1\% (95%CI 50.2‐74.7)), with 100% specificity for all the tests.

3)

Moving the S/CO ratio from Abbott assays from manufacturers recommended 1.4 to 0.28 improved sensitivity from 63% to 80%, without loss in specificity.

4)

Less than a third of samples positive for binding antibodies were also positive in the virus neutralization test (with 1:80 titer as a threshold) in the population‐based sample.