Seroprevalence of Anti-SARS-CoV-2 IgG and IgM among Adults over 65 Years Old in the South of Italy

Analysis of COVID-19 Incidence and Protective Potential of Persisting IgG Class Antibodies against SARS-CoV-2 Infection in Hospital Staff in Poland

The immune responses to both SARS-CoV-2 infection and vaccines are of key importance in prevention efforts. In April and May 2020, 703 study participants tested for COVID-19 by PCR tests were registered. In June and July 2020, they were examined for the presence of SARS-CoV-2 S1/S2 IgG. From October 2020 to January 2021, those among the study population with COVID-19 confirmed by PCR tests were registered, and the same group of participants was invited to be examined again for the presence of SARS-CoV-2 antibodies. In June 2020, antibodies were detected in only 88% of those who had PCR-confirmed COVID-19 in April-May 2020, which suggests that a significant proportion of persons in the Polish population do not produce antibodies after contact with SARS-CoV-2 antigens or rapidly lose them and reach levels below the lab detection limit. The levels of IgG class anti-SARS-CoV-2 antibodies were significantly lower among people who previously had COVID-19 than for those who had received COVID-19 vaccination, which confirms the high immunogenicity of the vaccines against COVID-19 in the Polish population. The study confirms that a detectable level of IgG class anti-SARS-CoV-2 antibodies cannot be considered a reliable marker of the presence and strength of COVID-19 immunity preventing individuals from acquiring SARS-CoV-2 infection.

Seroprevalence and SARS-CoV-2 invasion in general populations: A scoping review over the first year of the pandemic

Since the beginning of the COVID-19 pandemic, counting infected people has underestimated asymptomatic cases. This literature scoping review assessed the seroprevalence progression in general populations worldwide over the first year of the pandemic. Seroprevalence studies were searched in PubMed, Web of Science and medRxiv databases up to early April 2021. Inclusion criteria were a general population of all ages or blood donors as a proxy. All articles were screened for the title and abstract by two readers, and data were extracted from selected articles. Discrepancies were resolved with a third reader. From 139 articles (including 6 reviews), the seroprevalence estimated in 41 countries ranged from 0 to 69%, with a heterogenous increase over time and continents, unevenly distributed among countries (differences up to 69%) and sometimes among regions within a country (up to 10%). The seroprevalence of asymptomatic cases ranged from 0% to 31.5%. Seropositivity risk factors included low income, low education, low smoking frequency, deprived area residency, high number of children, densely populated centres, and presence of a case in a household. This review of seroprevalence studies over the first year of the pandemic documented the progression of this virus across the world in time and space and the risk factors that influenced its spread.

SARS-CoV-2 epidemiological trend before vaccination era: a seroprevalence study in Apulia, Southern Italy, in 2020

Aim

The present study aimed at assessing the prevalence of antibodies against SARS-CoV-2 in the general population in the province of Bari (Apulia region, Southern Italy) during the year 2020.

Subject and methods

In this study, 1325 serum samples collected from January to December 2020 were tested for the presence of IgM and IgG antibodies against whole-virus SARS-CoV-2 antigen by commercial ELISA. Positive samples were further tested by in-house ELISA for the detection of anti-receptor binding domain (RBD) IgM and IgG antibodies and by micro-neutralization (MN) assay for the detection of neutralizing antibody.

Results

One hundred (7.55%) samples had the presence of at least one antibody class against SARS-CoV-2 by commercial ELISA, of which 88 (6.6%) showed IgG and 19 (1.4%) showed IgM antibodies. The proportion of samples with IgG antibodies increased from 1.9% in January-February to 9.6% in November-December, while no significant increase was observed for IgM. When tested by in-house ELISA and MN assay, 17.0% and 31.6% were found positive to RBD IgG and RBD IgM, respectively, while 12.0% showed neutralizing antibody.

Conclusion

The proportion of samples with SARS-CoV-2 IgG antibodies increased during 2020, especially in the second half of the year, consistent with data reported by the routine epidemiological surveillance of SARS-CoV-2 cases. Despite the high number of reported cases, the seroprevalence values are relatively low, and only a small proportion of samples had neutralizing antibodies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10389-023-01834-3.

High seroconversion rate and SARS-CoV-2 Delta neutralization in people with HIV vaccinated with BNT162b2

OBJECTIVES

To assess humoral responses to SARS-CoV-2 Delta-variant in people with HIV (PWH) after BNT162b2-vaccination.

DESIGN

Multicenter cohort study of PWH with CD4 + cell count less than 500 cells/μl and viral load less than 50 copies/ml on stable antiretroviral therapy for at least 3 months.

METHODS

Anti-SARS-CoV-2 receptor-binding-domain IgG antibodies (anti-RBD IgG) were quantified and neutralization capacity was evaluated by ELISA/GenScript and virus-neutralization-test against the D614G-strain, beta and delta variants before vaccination (day 0) and 1 month after complete schedule (M1).

RESULTS

We enrolled 97 PWH, 85 received two vaccine shots. The seroconversion rate for anti-RBD IgG was 97% [95% confidence interval (CI) 90-100%] at M1. Median (IQR) anti-RBD IgG titer was 0.97 (0.97-5.3) BAU/ml at D0 and 1219 (602-1929) at M1. Neutralization capacity improved between D0 (15%; 50% CI 8-23%) and M1 (94%; 95% CI 87-98%) ( P  < 0.0001). At M1, NAbs against the D614G strain, beta and delta variants were present in 82, 77, and 84% PWH, respectively. The seroconversion rate and median anti-RBD-IgG level were 91% and 852 BAU/ml, respectively, in PWH with CD4 + cell count less than 250 ( n  = 13) and 98% and 1270 BAU/ml for CD4 + greater than 250 ( n  = 64) ( P  = 0.3994). NAbs were present in 73% of PWH with CD4 + less than 250 and 97% of those with CD4 + cell count greater than 250 ( P  = 0.0130). NAbs against beta variant were elicited in 50% in PWH with CD4 + cell count less than 250 and in 81% of those with CD4 + cell count greater than 250 ( P  = 0.0292). CD4 + and CD8 + T-cell counts were unchanged, whereas CD19 + B-cell counts decreased after vaccination(208 ± 124 at D0 vs. 188 ± 112 at M1, P  < 0.01). No notable adverse effects or COVID-19 cases were reported.

CONCLUSION

Seroconversion rates were high, with delta-neutralization rates similar to those for the D61G strain, after a two-dose BNT162b2 vaccination in PWH.

Predicting Antigenic Peptides from Rocio Virus NS1 Protein for Immunodiagnostic Testing Using Immunoinformatics and Molecular Dynamics Simulation

The mosquito-borne disease caused by the Rocio virus is a neglected threat, and new immune inputs for serological testing are urgently required for diagnosis in low-resource settings and epidemiological surveillance. We used in silico approaches to identify a specific antigenic peptide (p_ROCV2) in the NS1 protein of the Rocio virus that was theoretically predicted to be stable and exposed on its surface, where it demonstrated key properties allowing it to interact with antibodies. These findings related to the molecular dynamics of this peptide provide important insights for advancing diagnostic platforms and investigating therapeutic alternatives.

Humoral Immune Response Diversity to Different COVID-19 Vaccines: Implications for the "Green Pass" Policy

In the COVID-19 pandemic year 2021, several countries have implemented a vaccine certificate policy, the “Green Pass Policy” (GPP), to reduce virus spread and to allow safe relaxation of COVID-19 restrictions and reopening of social and economic activities. The rationale for the GPP is based on the assumption that vaccinated people should maintain a certain degree of immunity to SARS-CoV-2. Here we describe and compare, for the first time, the humoral immune response to mRNA-1273, BNT162b2, Ad26.COV2.S, and ChAdOx1 nCoV-19 vaccines in terms of antibody titer elicited, neutralizing activity, and epitope reactogenicity among 369 individuals aged 19 to 94 years. In parallel, we also considered the use of a rapid test for the determination of neutralizing antibodies as a tool to guide policymakers in defining booster vaccination strategies and eligibility for Green Pass. Our analysis demonstrates that the titer of antibodies directed towards the receptor-binding domain (RBD) of SARS-CoV-2 Spike is significantly associated with age and vaccine type. Moreover, natural COVID-19 infection combined with vaccination results, on average, in higher antibody titer and higher neutralizing activity as compared to fully vaccinated individuals without prior COVID-19. We also found that levels of anti-Spike RBD antibodies are not always strictly associated with the extent of inhibition of RBD-ACE2 binding, as we could observe different neutralizing activities in sera with similar anti-RBD concentrations. Finally, we evaluated the reactivity to four synthetic peptides derived from Spike protein on a randomly selected serum sample and observed that similar to SARS-CoV-2 infection, vaccination elicits a heterogeneous antibody response with qualitative individual features. On the basis of our results, the use of rapid devices to detect the presence of neutralizing antibodies, even on a large scale and repeatedly over time, appears helpful in determining the duration of the humoral protection elicited by vaccination. These aspects and their implications for the GPP are discussed.

Evaluation of FAST COVID-19 SARS-CoV-2 Antigen Rapid Test Kit for Detection of SARS-CoV-2 in Respiratory Samples from Mildly Symptomatic or Asymptomatic Patients

Molecular tests are the gold standard to diagnose severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection but are associated with a diagnostic delay, while antigen detection tests can generate results within 20 min even outside a laboratory. In order to evaluate the accuracy and reliability of the FAST COVID-19 SARS-CoV-2 Antigen Rapid Test Kit (Ag-RDT), two respiratory swabs were collected simultaneously from 501 patients, with mild or no coronavirus disease 2019 (COVID-19)-related symptoms, and analyzed with both the Reverse Transcriptase-quantitative Polymerase Chain Reaction (RT-qPCR) and the FAST COVID-19 SARS-CoV-2 Antigen Rapid Test. Results were then compared to determine clinical performance in a screening setting. We measured a precision of 97.41% (95% CI 92.42–99.15%) and a recall of 98.26% (95% CI 93.88–99.25%), with a specificity of 99.22% (95% CI 97.74–99.74%), a negative predictive value of 99.48% (95% CI 97.98–99.87%), and an overall accuracy of 99.00% (95% CI 97.69–99.68%). Concordance was described by a Kappa coefficient of 0.971 (95% CI 0.947–0.996). Considering short lead times, low cost, and opportunities for decentralized testing, the Ag-RDT test can enhance the efforts to control SARS-CoV-2 spread in several settings.

Identification of Immunogenic Linear B-Cell Epitopes in C. burnetii Outer Membrane Proteins Using Immunoinformatics Approaches Reveals Potential Targets of Persistent Infections

Coxiella burnetii is a global, highly infectious intracellular bacterium, able to infect a wide range of hosts and to persist for months in the environment. It is the etiological agent of Q fever—a zoonosis of global priority. Currently, there are no national surveillance data on C. burnetii’s seroprevalence for any South American country, reinforcing the necessity of developing novel and inexpensive serological tools to monitor the prevalence of infections among humans and animals—especially cattle, goats, and sheep. In this study, we used immunoinformatics and computational biology tools to predict specific linear B-cell epitopes in three C. burnetii outer membrane proteins: OMP-H (CBU_0612), Com-1 (CBU_1910), and OMP-P1 (CBU_0311). Furthermore, predicted epitopes were tested by ELISA, as synthetic peptides, against samples of patients reactive to C. burnetii in indirect immunofluorescence assay, in order to evaluate their natural immunogenicity. In this way, two linear B-cell epitopes were identified in each studied protein (OMP-H_(51–59), OMP-H_(91–106), Com-1_(57–76), Com-1_(191–206), OMP-P1_(197–209), and OMP-P1_(215–227)); all of them were confirmed as naturally immunogenic by the presence of specific antibodies in 77% of studied patients against at least one of the identified epitopes. Remarkably, a higher frequency of endocarditis cases was observed among patients who presented an intense humoral response to OMP-H and Com-1 epitopes. These data confirm that immunoinformatics applied to the identification of specific B-cell epitopes can be an effective strategy to improve and accelerate the development of surveillance tools against neglected diseases.

Impact of Two Different Recruitment Procedures (Random vs. Volunteer Selection) on the Results of Seroepidemiological Study (SARS-CoV-2)

The proper recruitment of subjects for population-based epidemiological studies is critical to the external validity of the studies and, above all, to the sound and correct interpretation of the findings. Since 2020, the novel coronavirus SARS-CoV-2 pandemic has been a new factor that has been, additionally, hindering studies. Therefore, the aim of our study is to compare demographic, socio-economic, health-related characteristics and the frequency of SARS-CoV-2 infection occurrence among the randomly selected group and the group composed of volunteers. We compare two groups of participants from the cross-sectional study assessing the seroprevalence of SARS-CoV-2 coronavirus, which was conducted in autumn 2020, in three cities of the Silesian Voivodeship in Poland. The first group consisted of a randomly selected, nationally representative, age-stratified sample of subjects (1167 participants, “RG” group) and was recruited using personal invitation letters and postal addresses obtained from a national registry. The second group (4321 volunteers, “VG” group) included those who expressed their willingness to participate in response to an advertisement published in the media. Compared with RG subjects, volunteers were more often females, younger and professionally active, more often had a history of contact with a COVID-19 patient, post-contact nasopharyngeal swab, fewer comorbidities, as well as declared the occurrence of symptoms that might suggest infection with SARS-CoV-2. Additionally, in the VG group the percentage of positive IgG results and tuberculosis vaccination were higher. The findings of the study confirm that surveys limited to volunteers are biased. The presence of the bias may seriously affect and distort inference and make the generalizability of the results more than questionable. Although effective control over selection bias in surveys, including volunteers, is virtually impossible, its impact on the survey results is impossible to predict. However, whenever possible, such surveys could include a small component of a random sample to assess the presence and potential effects of selection bias.

Sample-Pooling Strategy for SARS-CoV-2 Detection among Students and Staff of the University of Sannio

Since the beginning of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pandemic, it has been clear that testing large groups of the population was the key to stem infection and prevent the effects of the coronavirus disease of 2019, mostly among sensitive patients. On the other hand, time and cost-sustainability of virus detection by molecular analysis such as reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) may be a major issue if testing is extended to large communities, mainly asymptomatic large communities. In this context, sample-pooling and test grouping could offer an effective solution. Here we report the screening on 1195 oral-nasopharyngeal swabs collected from students and staff of the Università degli Studi del Sannio (University of Sannio, Benevento, Campania, Italy) and analyzed by an in-house developed multiplex RT-qPCR for SARS-CoV-2 detection through a simple monodimensional sample pooling strategy. Overall, 400 distinct pools were generated and, within 24 h after swab collection, five positive samples were identified. Out of them, four were confirmed by using a commercially available kit suitable for in vitro diagnostic use (IVD). High accuracy, sensitivity and specificity were also determined by comparing our results with a reference IVD assay for all deconvoluted samples. Overall, we conducted 463 analyses instead of 1195, reducing testing resources by more than 60% without lengthening diagnosis time and without significant losses in sensitivity, suggesting that our strategy was successful in recognizing positive cases in a community of asymptomatic individuals with minor requirements of reagents and time when compared to normal testing procedures.