Seropositive Individuals Research Articles

Differences in the Concentration of Anti-SARS-CoV-2 IgG Antibodies Post-COVID-19 Recovery or Post-Vaccination.

At the end of 2020, population-based vaccination programs with new generation mRNA-based vaccines began almost all over the world. The aim of the study was to evaluate the titer of anti-SARS-CoV-2 IgG antibodies against the S1 subunit of the virus’s spike protein as a marker of the humoral response in 477 patients and the concentration of interferon-gamma as an indicator of cellular response in 28 individuals. In our studies, we used serological enzyme-linked immunosorbent assays. IgG was measured in weeks 2 and 3 after the first dose and 1–5 weeks after the second dose of an mRNA vaccine in seropositive and seronegative individuals as well as in symptomatic and asymptomatic convalescents. High levels of antibodies were observed in 98% of our vaccinated cohort, and the presence of protective T cells was confirmed in the blood samples of all participants. The humoral immune response is diversified and is visible as early as 2–3 weeks after the first dose of the mRNA vaccine. The level of protection increased significantly after the second dose, with the increase being much greater in pre-vaccine healthy subjects and less in convalescents. In the second and third weeks after the second dose, the concentration of IgG antibodies was the highest, and in the following weeks, it decreased gradually. Regular serological measurements on eight subjects show that antibody titers are lower four months after vaccination than before the second dose.

Immunoglobulin G antibody response to the Sputnik V vaccine: previous SARS-CoV-2 seropositive individuals may need just one vaccine dose

Introduction: We evaluated the immunoglobulin (Ig) G antibody response against the nucleocapsid protein (NP) and the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2 in a cohort of 86 individuals in Venezuela, before and after receiving the Sputnik V vaccine.Methods: Antibody responses against NP and RBD were determined with an enzyme-linked immunosorbent assay just before, 3 weeks after the first, and 6 weeks after the second dose of the vaccine.Results: Before vaccination, 59 individuals were seronegative, and 27 seropositive for NP and/or RBD. Of the seronegative cohort, 42% did not develop an IgG immune response against RBD after the first vaccine dose, but 100% had a strong IgG response after 2 doses. All seropositive individuals developed a strong IgG antibody response against RBD after the first vaccine dose, with antibody levels ∼40% higher than seronegative individuals who had received 2 doses. Previously seropositive subjects showed no significant increase in IgG antibody response against RBD after the second vaccine dose.Conclusions: We demonstrate that 2 doses of the Sputnik V vaccine triggered antibody response in all study individuals. The second Sputnik V dose had no impact on IgG response for those seropositive for SARS-CoV-2 antigens before vaccination.

Seroprevalence of SARS-CoV-2 antibodies among rural healthcare workers.

The objective of this longitudinal cohort study was to determine the seroprevalence of antibodies to severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2) in healthcare workers employed at healthcare settings in three rural counties in eastern South Dakota and western Minnesota from May 13, 2020, through December 22, 2020. Three blood draws were performed at five clinical sites and tested for the presence of antibodies against the SARS‐CoV‐2. Serum samples were tested for the presence of antibodies using a fluorescent microsphere immunoassay (FMIA), neutralization of SARS‐CoV‐2 spike‐pseudotyped particles (SARS‐CoV‐2pp) assay, and serum virus neutralization (SVN) assay. The seroprevalence was determined to be 1/336 (0.29%) for samples collected from 5/13/20 to 7/13/20, 5/260 (1.92%) for samples collected from 8/13/20 to 9/25/20, and 35/235 (14.89%) for samples collected from 10/16/20 to 12/22/20. Eight of the 35 (22.8%) seropositive individuals identified in the final draw did not report a previous diagnosis with COVID‐19. There was a high correlation (>90%) between the FMIA and virus neutralization assays. Each clinical site's seroprevalence was higher than the cumulative incidence for the general public in the respective county as reported by state public health agencies. As of December 2020, there was a high percentage (85%) of seronegative individuals in the study population.

Target product profile for a dengue pre-vaccination screening test.

With increasing geographic spread, frequency, and magnitude of outbreaks, dengue continues to pose a major public health threat worldwide. Dengvaxia, a dengue live-attenuated tetravalent vaccine, was licensed in 2015, but post hoc analyses of long-term data showed serostatus-dependent vaccine performance with an excess risk of hospitalized and severe dengue in seronegative vaccine recipients. The World Health Organization (WHO) recommended that only persons with evidence of past dengue infection should receive the vaccine. A test for pre-vaccination screening for dengue serostatus is needed. To develop the target product profile (TPP) for a dengue pre-vaccination screening test, face-to-face consultative meetings were organized with follow-up regional consultations. A technical working group was formed to develop consensus on a reference test against which candidate pre-vaccination screening tests could be compared. The group also reviewed current diagnostic landscape and the need to accelerate the evaluation, regulatory approval, and policy development of tests that can identify seropositive individuals and maximize public health impact of vaccination while avoiding the risk of hospitalization in dengue-naive individuals. Pre-vaccination screening strategies will benefit from rapid diagnostic tests (RDTs) that are affordable, sensitive, and specific and can be used at the point of care (POC). The TPP described the minimum and ideal characteristics of a dengue pre-vaccination screening RDT with an emphasis on high specificity. The group also made suggestions for accelerating access to these RDTs through streamlining regulatory approval and policy development. Risk and benefit based on what can be achieved with RDTs meeting minimal and optimal characteristics in the TPP across a range of seroprevalences were defined. The final choice of RDTs in each country will depend on the performance of the RDT, dengue seroprevalence in the target population, tolerance of risk, and cost-effectiveness.

Performance assessment of a multi-epitope chimeric antigen for the serological diagnosis of acute Mayaro fever

Mayaro virus (MAYV), which causes mayaro fever, is endemic to limited regions of South America that may expand due to the possible involvement of Aedes spp. mosquitoes in its transmission. Its effective control will require the accurate identification of infected individuals, which has been restricted to nucleic acid-based tests due to similarities with other emerging members of the Alphavirus genus of the Togaviridae family; both in structure and clinical symptoms. Serological tests have a more significant potential to expand testing at a reasonable cost, and their performance primarily reflects that of the antigen utilized to capture pathogen-specific antibodies. Here, we describe the assembly of a synthetic gene encoding multiple copies of antigenic determinants mapped from the nsP1, nsP2, E1, and E2 proteins of MAYV that readily expressed as a stable chimeric protein in bacteria. Its serological performance as the target in ELISAs revealed a high accuracy for detecting anti-MAYV IgM antibodies. No cross-reactivity was observed with serum from seropositive individuals for dengue, chikungunya, yellow fever, Zika, and other infectious diseases as well as healthy individuals. Our data suggest that this bioengineered antigen could be used to develop high-performance serological tests for MAYV infections.

Humoral immune responses during SARS-CoV-2 mRNA vaccine administration in seropositive and seronegative individuals

BackgroundThe global pandemic of coronavirus disease 2019 (COVID-19) is caused by infection with the SARS-CoV-2 virus. Currently, there are three approved vaccines against SARS-CoV-2 in the USA, including two based on messenger RNA (mRNA) technology that has demonstrated high vaccine efficacy. We sought to characterize humoral immune responses, at high resolution, during immunization with the BNT162b2 (Pfizer-BioNTech) vaccine in individuals with or without prior history of natural SARS-CoV-2 infection.MethodsWe determined antibody responses after each dose of the BNT162b2 SARS-CoV-2 vaccine in individuals who had no prior history of SARS-CoV-2 infection (seronegative) and individuals that had previous viral infection 30–60 days prior to first vaccination (seropositive). To do this, we used both an antibody isotype-specific multiplexed bead-based binding assays targeting multiple SARS-CoV-2 viral protein antigens and an assay that identified potential SARS-CoV-2 neutralizing antibody levels. Moreover, we mapped antibody epitope specificity after immunization using SARS-CoV-2 spike protein peptide arrays.ResultsAntibody levels were significantly higher after a single dose in seropositive individuals compared to seronegative individuals and were comparable to levels observed in seronegative individuals after two doses. While IgG was boosted by vaccination for both seronegative and seropositive individuals, only seronegative individuals had increased IgA or IgM antibody titers after primary immunization. We identified immunodominant peptides targeted on both SARS-CoV-2 spike S1 and S2 subunits after vaccination.ConclusionThese findings demonstrated the antibody responses to SARS-CoV-2 immunization in seropositive and seronegative individuals and provide support for the concept of using prior infection history as a guide for the consideration of future vaccination regimens. Moreover, we identified key epitopes on the SARS-CoV-2 spike protein that are targeted by antibodies after vaccination that could guide future vaccine and immune correlate development.

Stability of SARS-CoV-2 IgG in multiple laboratory conditions and blood sample types.

Background: COVID-19 seroprevalence studies use serum/plasma samples to detect SARS-CoV-2 IgG. Data supporting alternate specimen types and freeze-thaw antibody stability is lacking. The stability of IgG and other immunoglobulins in multiple blood sample types stored in differing conditions and multiple freeze-thaw cycles (FTCs) was evaluated.Materials and methods: Serum, plasma, and heparinized-plasma samples were collected from COVID-19 recovered individuals. Samples underwent testing for SARS-CoV-2 antibodies upon collection, after each of 10–12 FTCs, and storage at -70°C, -20°C, 4°C, and room-temperature for 10–12 days using four high-throughput commercial assays, two rapid-test cassettes, a manual ELISA, and a surrogate neutralization assay.Results: All three specimen types were collected from 34 COVID-19 recovered seropositive individuals (≥21 days post-symptoms). Using the Architect and Liaison assays, a positive qualitative SARS-CoV-2 IgG result was detected daily up to 12 FTCs and up to 10 days of storage at different temperatures. An additional 25 plasma samples consistently demonstrated detection of SARS-CoV-2 antibodies daily after 12 FTCs and storage at -20°C using two rapid test cassette assays (SD Biosensor and Hangzhou All Test), manual (Beijing Wantai) and surrogate neutralization (GenScript) ELISAs, and two high-throughput assays (Roche Elecsys nucleocapsid and spike). IgM antibodies were less frequently detected by one of the rapid test cassette assays.Conclusions: Serum, plasma, and heparinized-plasma constitute reliable samples for SARS-CoV-2 antibody detection. In particular, the IgG response was stable and reliably detected after multiple FTCs and storage at common laboratory conditions. IgM detection was variable due to the labile nature of this antibody class.

Humoral immunity to SARS-CoV-2 and seasonal coronaviruses in children and adults in north-eastern France.

BackgroundChildren are underrepresented in the COVID-19 pandemic and often experience milder disease than adolescents and adults. Reduced severity is possibly due to recent and more frequent seasonal human coronaviruses (HCoV) infections. We assessed the seroprevalence of SARS-CoV-2 and seasonal HCoV specific antibodies in a large cohort in north-eastern France.MethodsIn this cross-sectional seroprevalence study, serum samples were collected from children and adults requiring hospital admission for non-COVID-19 between February and August 2020. Antibody responses to SARS-CoV-2 and seasonal HCoV (229E, HKU1, NL63, OC43) were assessed using a bead-based multiplex assay, Luciferase-Linked ImmunoSorbent Assay, and a pseudotype neutralisation assay.FindingsIn 2,408 individuals, seroprevalence of SARS-CoV-2-specific antibodies was 7-8% with three different immunoassays. Antibody levels to seasonal HCoV increased substantially up to the age of 10. Antibody responses in SARS-CoV-2 seropositive individuals were lowest in adults 18-30 years. In SARS-CoV-2 seronegative individuals, we observed cross-reactivity between antibodies to the four HCoV and SARS-CoV-2 Spike. In contrast to other antibodies to SARS-CoV-2, specific antibodies to sub-unit 2 of Spike (S2) in seronegative samples were highest in children. Upon infection with SARS-CoV-2, antibody levels to Spike of betacoronavirus OC43 increased across the whole age spectrum. No SARS-CoV-2 seropositive individuals with low levels of antibodies to seasonal HCoV were observed.InterpretationOur findings underline significant cross-reactivity between antibodies to SARS-CoV-2 and seasonal HCoV, but provide no significant evidence for cross-protective immunity to SARS-CoV-2 infection due to a recent seasonal HCoV infection. In particular, across all age groups we did not observe SARS-CoV-2 infected individuals with low levels of antibodies to seasonal HCoV.FundingThis work was supported by the « URGENCE COVID-19 » fundraising campaign of Institut Pasteur, by the French Government's Investissement d'Avenir program, Laboratoire d'Excellence Integrative Biology of Emerging Infectious Diseases (Grant No. ANR-10-LABX-62-IBEID), and by the REACTing (Research & Action Emerging Infectious Diseases), and by the RECOVER project funded by the European Union's Horizon 2020 research and innovation programme under grant agreement No. 101003589, and by a grant from LabEx IBEID (ANR-10-LABX-62-IBEID).

Experience in Studying Herd and Individual Immunity to the SARS-CoV-2 Virus in Medical Workers

The aim was to study SARS-CoV-2 immunity among medical workers in Kazan.Materials and methods. Studied were serum samples from 348 medical workers from 10 medical organizations in Kazan, divided into groups according to the level of the alleged risk of infection of employees. To determine IgG, a two-stage direct version of the solid-phase ELISA and the test-system “SARS-CoV-2-IgG-ELISA-BEST” (Russia) were used.Results and discussion. At the time of the study and over the previous three months, the examined medical workers had no symptoms of acute respiratory viral infection or respiratory tract infections; there were negative results of examining nasopharyngeal/ oropharyngeal swabs for the presence of SARS-CoV-2 RNA. Seroprevalence for IgG to SARS-CoV-2 virus for different medical organizations in Kazan ranged within the scope of 3.3–30.8 % and averaged 16.4 %. The wide variation in seroprevalence values in medical workers of different medical organizations may indicate different levels of intensity of professional contacts and the effectiveness of anti-epidemic measures in these medical organizations. Among medical workers with seropositive results, the prevalence of persons with a very high coefficient of positivity (49.1 %) is observed, which characterizes high level of antiviral antibodies. The presence of a high proportion of seropositive individuals among medical workers, who have had an asymptomatic form of COVID-19 confirms the high intensity of the latent epidemic process, which must be taken into account when organizing preventive measures, including vaccination.

Peculiarities of Seroprovalence to SARS-CoV-2 in the Population of the Middle and Southern Urals in the Early Period of the COVID-19 Pandemic

Relevance. At the end of 2019, the world was confronted with a novel coronavirus (SARS-CoV-2), In January 2020, WHO declared an epidemic related to SARS-CoV-2, a health emergency of international importance, and in March characterized the spread of the world. diseases like a pandemic.Purpose of the study. Conduct a comparative analysis of the seroprevalence of the population of the Sverdlovsk and Chelyabinsk regions – the largest administrative territorial entities of the Middle and Southern Urals – against the backdrop of the COVID-19 pandemic.Materials and methods. The work was carried out under the program of the first stage of assessing the seroprevalence of the population of the Russian Federation according to a unified methodology developed by Rospotrebnadzor of the Russian Federation with the participation of the Saint Petersburg Pasteur Institute. The selection of participants was carried out by the method of questioning and randomization. The presence of antibodies to the SARS-CoV-2 nucleocapsid was determined in blood serum by the enzyme immunoassay.Results. Comparative analysis of the results showed that the incidence rate of COVID-19 in the Chelyabinsk region was consistently lower, and the seroprevalence at the first stage of the study was statistically significantly higher (p <0/05) than in the Sverdlovsk region. It was found that the incidence in both regions had a direct correlation with population density (r = 0.59; p <0.05). There were no differences between the compared areas in terms of seroprevalence among convalescents, people who had contact with COVID-19 patients, and asymptomatic volunteers with a positive PCR test. When analyzing seroprevalent volunteers in both regions, it was shown that the number of asymptomatic individuals varied within 94.4 ± 1.2% – 95.0 ± 0.95%. These data indicate that the majority of volunteers tolerated COVID-19 asymptomatically.Conclusions. A comparative study showed a statistically significant predominance of seroprevalence among the population of the Chelyabinsk region. It was found that an increase in seroprevalence at the population level was accompanied by a decrease in morbidity. Shown is a direct relationship between population density and the incidence rate. More than 90% of seropositive individuals in the compared areas showed asymptomatic course of coronavirus infection.

Prospective case-control study of cardiovascular abnormalities six months following mild COVID-19 in healthcare workers

Funding AcknowledgementsType of funding sources: Public Institution(s). Main funding source(s): Barts Charity UCLH CharityOnBehalfCOVIDsortiumBackgroundRecent CMR studies have reported cardiac abnormalities after COVID-19 are common, even after mild, non-hospitalised illness with evidence of ongoing myocardial inflammation. Such a prevalence of chronic myocarditis after mild disease has prompted societal concerns in diverse domains, and suggests that screening should be considered post COVID-19, even in asymptomatic individuals. Cardiovascular magnetic resonance (CMR) has proven utility for diagnosis in patients with COVID-19 infection and elevated troponin from unclear causes by measuring cardiac structure, function, myocardial scar (late gadolinium enhancement) and oedema (T1 and T2 mapping).ObjectivesWe aimed to determine the prevalence and extent of late cardiac and cardiovascular sequelae after mild non-hospitalised SARS-CoV-2 infection.MethodsParticipants were recruited from COVIDsortium, a three-hospital prospective study of 731 healthcare workers who underwent first wave weekly symptom, PCR and serology assessment over 4 months, with seroconversion in 21.5% (n = 157). At 6 months post infection, 74 seropositive and 75 age-, sex-, ethnicity-matched seronegative controls were recruited for cardiovascular phenotyping (comprehensive phantom-calibrated Cardiovascular Magnetic Resonance and blood biomarkers). Analysis was blinded, using objective AI analytics where available.Results149 subjects (mean age 37 years, range 18-63, 58% female) were recruited. Seropositive infections had been mild with case definition/non-case definition/asymptomatic disease in 45(61%), 18(24%) and 11(15%) with one person hospitalised (for 2 days). Between seropositive and seronegative groups, there were no differences in cardiac structure (left ventricular volumes, mass; atrial area), function (ejection fraction, global longitudinal shortening, aortic distensibility), tissue characterisation (T1, T2, ECV mapping, late gadolinium enhancement) or biomarkers (troponin, NT-proBNP). With abnormal defined by the 75 seronegatives (2 standard deviations from mean, e.g. EF < 54%, septal T1 > 1072ms, septal T2 > 52.4ms), individuals had abnormalities including reduced EF (n = 2, minimum 50%), T1 elevation (n = 6), T2 elevation (n = 9), LGE (n = 13, median 1%, max 5% of myocardium), biomarker elevation (borderline troponin elevation in 4; all NT-proBNP normal). These were distributed equally between seropositive and seronegative individuals.ConclusionsCardiovascular abnormalities are no more common in seropositive vs seronegative otherwise healthy, workforce representative individuals 6 months post mild SARS-CoV-2 infection. Our study provides societal reassurance for the cardiovascular health of working-aged individuals with convalescence from mild SARS-CoV-2. Screening asymptomatic individuals following mild diseases is not indicated.

African swine fever endemic persistence in wild boar populations: Key mechanisms explored through modelling.

African swine fever (ASF) is a serious global concern from an ecological and economic point of view. While it is well established that its main transmission routes comprise contact between infected and susceptible animals and transmission through contaminated carcasses, the specific mechanism leading to its long‐term persistence is still not clear. Among others, a proposed mechanism involves the potential role of convalescent individuals, which would be able to shed the virus after the end of the acute infection. Using a spatially explicit, stochastic, individual‐based model, we tested: (1) if ASF can persist when transmission occurs only through infected wild boars and infected carcasses; (2) if the animals that survive ASF can play a relevant role in increasing ASF persistence chances; (3) how hunting pressure can affect the ASF probability to persist. The scenario in which only direct and carcass‐mediated transmission were contemplated had 52% probability of virus persistence 10 years after the initial outbreak. The inclusion of survivor‐mediated transmission corresponded to slightly higher persistence probabilities (57%). ASF prevalence during the endemic phase was generally low, ranging 0.1–0.2%. The proportion of seropositive individuals gradually decreased with time and ranged 4.5–6.6%. Our results indicate that direct and carcass‐mediated infection routes are sufficient to explain and justify the long‐term persistence of ASF at low wild boar density and the ongoing geographic expansion of the disease front in the European continent. During the initial years of an ASF outbreak, hunting should be carefully evaluated as a management tool, in terms of potential benefits and negative side‐effects, and combined with an intensive effort for the detection and removal of wild boar carcasses. During the endemic phase, further increasing hunting effort should not be considered as an effective strategy. Additional effort should be dedicated to finding and removing as many wild boar carcasses as possible.

A three-phase population based sero-epidemiological study: Assessing the trend in prevalence of SARS-CoV-2 during COVID-19 pandemic in Jordan

The evolution of the COVID-19 pandemic in Jordan during the first 10 months of the epidemic was peculiar and can be easily categorized in three different phases: a first period featuring a very low number of reported cases, a second period with exponential growth from August with up to 8000 cases on the 18th November 2020, and a third phase with steady and progressive decline of the epidemiological curve. With the aim of better determine the entity of the population exposed to SARS-CoV-2, the Jordan Ministry of Health with the support of the WHO launched three rounds of the nationwide sero-prevalence survey. Using population proportionate to size (PPS) methodology, around 5000 individuals were selected from all Jordan governorates. Blood samples were collected from all participants and ELISA assays for total IgM, IgG antibodies to COVID-19 were used for testing at the National Public Health Laboratory. Results revealed that seroprevalence dramatically increased over time, with only a tiny fraction of seropositive individuals in August (0.3%), to increase up to more than 20-fold in October (7.0%) and to reach one-third of the overall population exposed by the end of 2020 (34.2%). While non age-specific trends were detected in infection rates across different age categories, in all three rounds of the seroprevalence study two out of three positive participants did not report any sign and/or symptom compatible with COVID-19. The serial cross-sectional surveys experience in Jordan allowed to gain additional insights of the epidemic over time in combination with context-specific aspects like adherence to public health and social measures (PHSM). On the other hand, such findings would be helpful for planning of public health mitigation measures like vaccinations and tailored restriction policies.

Antibody Response against the SARS-CoV-2 Nucleocapsid Protein and Its Subdomains—Identification of Pre-Immunization Status by Human Coronaviruses with Multipanel Nucleocapsid Fragment Immunoblotting

A novel beta coronavirus that emerged in late December 2019 triggered a global pandemic. Diagnostic methods for rapid identification of infected individuals were established in new biotechnological approaches. Vaccine production and application to individuals and measurement of SARS-CoV-2 antibodies also began. Serum samples from 240 health care workers were collected at three-month intervals over nine months. Indirect SARS-CoV-2 nucleocapsid IgG ELISA tests were used to identify humoral immune responses. All seropositive individuals and those with borderline ELISA values were tested with a specifically generated multipanel nucleocapsid fragment immunoblot. Of the 240 individuals, 24 showed seroconversion in ELISA after experiencing COVID-19. All of them showed a positive reaction against the full-length nucleocapsid protein in the immunoblot. The highest reactivity was seen either against fragment N(100–300) or in a minority against the posterior part N(200–419). In general, the staining pattern of COVID-19 patients showed four phenotypes. In contrast, three individuals classified as borderline by ELISA reacted exclusively with fragments N(1–220) and N(100–300) containing the octamer amino acid sequence FYYLGTGP, which is identical in human coronaviruses sharing this sequence with SARS-CoV-2. These represent a unique and thus fifth phenotype. This work suggests the existence of distinct phenotypic patterns of IgG production towards N-protein subdomains.

Cohabitation With a Known Coronavirus Disease 2019 Case Is Associated With Greater Antibody Concentration and Symptom Severity in a Community-Based Sample of Seropositive Adults.

In a community-based sample of seropositive adults (n = 1101), we found that seropositive individuals who lived with a known coronavirus disease 2019 (COVID-19) case exhibited higher blood anti–severe acute respiratory syndrome coronavirus 2 spike receptor-binding domain immunoglobulin G concentrations and greater symptom severity compared to seropositive individuals who did not live with a known COVID-19 case.

Assessment of initial SARS-CoV-2 seroprevalence in the most affected districts in the municipality of São Paulo, Brazil

BackgroundSão Paulo city has been one of the regions most affected by the COVID-19 pandemic in Brazil. Frequent asymptomatic and oligosymptomatic infections and poor access to diagnostic tests make serosurveys crucial to monitor the magnitude of the epidemic and to inform public health policies, such as vaccination plans. ObjectivesTo estimate, early in the epidemic, the seroprevalence of antibodies to SARS-CoV-2 in adults living in the six most affected districts in São Paulo city, and to assess potential associated risk factors. MethodsThis was a cross-sectional population-based survey of 1,152 households randomly selected from 72 census tracts. During the period May 4–12, 2020, 463 participants completed a questionnaire on sociodemographic characteristics and history of symptoms in the past two weeks, and provided a blood sample. Prevalence of SARS-CoV-2 antibodies was the outcome of interest and was estimated based on results of two immunoassays, Maglumi SARS-CoV-2 chemiluminescence assay Immunoglobulin (Ig) M (IgM) and IgG, and Roche electrochemiluminescence assay total Ig. Serum samples reactive to either assay were considered positive. ResultsWeighted overall seroprevalence was 6% (95%CI 3.9–8.3%). No association was observed between seropositivity and sex, age group or education level. Participants who reported black and brown skin color showed a 2.7 fold higher prevalence than people with white skin (p = 0.007). Among the 30 seropositive individuals, 14 (46.6%) reported no COVID-19 compatible symptoms in the past two weeks. ConclusionThis study represents the first assessment of SARS-CoV-2 seroprevalence in the city of São Paulo and 6% is the baseline estimate of a series of population-based seroprevalence surveys. Serological screening using sound serological assays is the key tool to monitoring temporal and geographic changes in the spread of the virus through an important epicenter of the COVID-19 pandemic in Brazil. Ultimately, it may inform prevention and control efforts.

Persistence of humoral response upon SARS-CoV-2 infection.

SummarySARS‐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.

High SARS-CoV-2 seroprevalence in children and adults in the Austrian ski resort of Ischgl

BackgroundIn early March 2020, a SARS-CoV-2 outbreak in the ski resort Ischgl in Austria initiated the spread of SARS-CoV-2 throughout Austria and Northern Europe.MethodsBetween April 21st and 27th 2020, a cross-sectional epidemiologic study targeting the full population of Ischgl (n = 1867), of which 79% could be included (n = 1473, incl. 214 children), was performed. For each individual, the study involved a SARS-CoV-2 PCR, antibody testing and structured questionnaires. A mathematical model was used to help understand the influence of the determined seroprevalence on virus transmission.ResultsThe seroprevalence was 42.4% (95% confidence interval (CI) 39.8–44.7). Individuals under 18 showed a significantly lower seroprevalence of 27.1% (95% CI 21.3-33.6) than adults (45%; 95% CI 42.2–47.7; OR of 0.455, 95% CI 0.356–0.682, p < 0.001). Of the seropositive individuals, 83.7% had not been diagnosed to have had SARS-CoV-2 infection previously. The clinical course was generally mild. Over the previous two months, two COVID-19-related deaths had been recorded, corresponding to an infection fatality rate of 0.25% (95% CI 0.03–0.91). Only 8 (0.5 %) individuals were newly diagnosed to be infected with SARS-CoV-2 during this study.ConclusionsIschgl was hit early and hard by SARS-CoV-2 leading to a high local seroprevalence of 42.4%, which was lower in individuals below the age of 18 than in adults. Mathematical modeling suggests that a drastic decline of newly infected individuals in Ischgl by the end of April occurred due to the dual impact from the non-pharmacological interventions and a high immunization of the Ischgl population.

NK Cell Diversity Influences Outcomes after Cord Blood Transplantation

Natural killer (NK) cells are the first subset of lymphocytes to reconstitute, and likely play an important role in the graft-versus-leukemia response early after allogeneic hematopoietic stem cell transplantation. NK cells are highly diverse, and express an array of activating and inhibiting receptors, which delicately regulate their activation status.To provide a framework to better understand NK cell development and maturation after cord blood transplantation (CBT) and its implication on clinical outcomes, we designed a mass cytometry (also known as cytometry by time of flight) panel of 40 monoclonal antibodies recognizing lineage markers, NK cell receptors and transcription factors to interrogate the NK cell repertoire in prospectively collected peripheral blood (PB) samples from 60 CBT recipients. The resultant high-dimensional single cell data were analyzed by t-Distributed Stochastic Neighbor Embedding (t-SNE) dimension reduction algorithm to generate expression profile graphs.With this mass cytometry platform, we first interrogated and compared the NK cell repertoire in CB (n=10) and adult peripheral blood (PB) (n=20) and used inverse Simpson index to measure the diversity of the NK cell populations. NK cells from CB donors had a significantly lower diversity (median 537, range 311-891) compared to NK cells from healthy adult PB donors (median 2858, range 1228-5630; p<0.0001). Since CMV infection has been shown to drive NK cell maturation, we next asked if CMV infection also alters NK cell diversity by comparing the diversity of the NK cell repertoire in CB (n=10), and in PB from adult healthy donors who were either CMV-seropositive (n=10), or CMV-seronegative (n=10). The diversity of the NK cell repertoire was significantly greater in CMV seropositive healthy individuals (median 4217, range 2672-5630) compared to CMV-seronegative healthy adults (median 2247 , range 2026-2468; P=0.0002) and cord blood donors (median 537, range 311-891; P<0.0001), pointing to an important role for CMV infection in driving NK diversity.Harnessing mass cytometry, we undertook an in-depth examination of the NK repertoire in prospectively collected PB samples from 60 CBT recipients. We first sought to determine if CMV infection early after CBT can drive NK cell maturation and accelerate the acquisition of a diverse repertoire. The median time to CMV reactivation for the cohort was 71 days. CMV reactivation in the first 100 days after CBT (n=25) was associated with significantly greater NK diversity (median 844, range 198-1196) when compared to patients without CMV reactivation (median 405, range 110-889; p=0.0003). Notably, CMV augmented NK diversity mainly in the KIR+ population (median 743, range 207-1500) compared to the KIR- population (median 361, range 92-1038; p=0.007); while in the absence of CMV reactivation, NK cell diversity in the KIR+ and KIR- populations remained similar (median 305, range 102-702 vs. median 332, range 54-830; p=0.98). These data indicate that CMV infection augments NK diversity after CBT, and that this effect is most pronounced within the KIR+ population.We next determined if NK cell diversity can influence outcomes by comparing the diversity of the NK cell repertoire in PB samples collected in the first 100 days after CBT from 15 patients who went on to relapse compared to 45 patients who remained in remission for 2 years. NK cell diversity was significantly higher (median 839, range 416-1069) in patients who remained in remission compared to those who progressed and relapsed (median 446, range 328-925; p=0.03). Moreover, the greatest difference in diversity in the two groups was noted within the KIR+ population (median 788, range 101-1500 for patients in remission vs median 320, range 177-857 for patients who relapsed; p=0.002).In summary, we have used multiparametric mass cytometry to examine expression of 40 NK markers, and to gain insights into the diversity of the NK cell repertoire after CBT. We have shown that CB NK cells have a limited NK cell diversity, which increases in breadth and subsets after transplant. Moreover, we observed that CMV infection reconfigures the NK cell compartment and drives the diversity of the NK cell repertoire, especially within the KIR+ population. These data may provide the basis to rationally design therapeutic strategies that can modulate NK diversity in the settings of infection and transplant. DisclosuresNo relevant conflicts of interest to declare.

Seroprevalence of anti-SARS-CoV-2 IgG in asymptomatic and pauci-symptomatic people over a 5 month survey in Argentina.

ABSTRACTObjective.To evaluate the seroprevalence of COVID-19 infection in pauci-symptomatic and asymptomatic people, the associated epidemiological factors, and IgG antibody kinetic over a 5-month period to get a better knowledge of the disease transmissibility and the rate of susceptible persons that might be infected.Methods.Seroprevalence was evaluated by a cross-sectional study based on the general population of Santa Fe, Argentina (non-probabilistic sample) carried out between July and November 2020. A subgroup of 20 seropositive individuals was followed-up to analyze IgG persistence. For the IgG anti-SARS-CoV-2 antibodies detection, the COVID-AR IgG® ELISA kit was used.Results.3 000 individuals were included conforming asymptomatic and pauci-symptomatic groups (n=1 500 each). From the total sample, only 8.83% (n=265) presented reactivity for IgG anti-SARS-CoV-2. A significant association was observed between positive anti-SARS-CoV-2 IgG and a history of contact with a confirmed case; the transmission rate within households was approximately 30%. In the pauci-symptomatic group, among the seropositive ones, anosmia and fever presented an OR of 16.8 (95% CI 9.5-29.8) and 2.7 (95% CI 1.6-4.6), respectively (p <0.001). In asymptomatic patients, IgG levels were lower compared to pauci-symptomatic patients, tending to decline after 4 months since the symptoms onset.Conclusion.We observed a low seroprevalence, suggestive of a large population susceptible to the infection. Anosmia and fever were independent significant predictors for seropositivity. Asymptomatic patients showed lower levels of antibodies during the 5-month follow-up. IgG antibodies tended to decrease over the end of this period regardless of symptoms.