Persistence and decay of human antibody responses to the receptor binding domain of SARS-CoV-2 spike protein in COVID-19 patients

A combined strategy to detect plasma samples reliably with high anti-SARS-CoV-2 neutralizing antibody titers in routine laboratories

The determination of anti-SARS-CoV-2 neutralizing antibodies (NAbs) is of interest in many respects. High NAb titers, for example, are the most important criterion regarding the effectiveness of convalescent plasma therapy. However, common cell culture-based NAb assays are time-consuming and feasible only in special laboratories. Our data reveal the suitability of a novel ELISA-based surrogate virus neutralization test (sVNT) to easily measure the inhibition-capability of NAbs in the plasma of COVID-19 convalescents. We propose a combined strategy to detect plasma samples with high NAb titers (≥ 1:160) reliably and to, simultaneously, reduce the risk of erroneously identifying low-titer specimens. For this approach, results of the sVNT assay are compared to and combined with those acquired from the Euroimmun anti-SARS-CoV-2 IgG assay. Both assays are appropriate for high-throughput screening in standard BSL-2 laboratories. Our measurements further show a long-lasting humoral immunity of at least 11 months after symptom onset.

Clinical Course of SARS-CoV-2 Infection in Adults with ESKD Receiving Outpatient Hemodialysis

Background

Patients with ESKD on maintenance dialysis receive dialysis in common spaces with other patients and have a higher risk of severe SARS-CoV-2 infections. They may have persistently or intermittently positive SARS-CoV-2 RT-PCR tests after infection. We describe the clinical course of SARS-CoV-2 infection and the serologic response in a convenience sample of patients with ESKD to understand the duration of infectivity.

Methods

From August to November 2020, we enrolled patients on maintenance dialysis with SARS-CoV-2 infections from outpatient dialysis facilities in Atlanta, Georgia. We followed participants for approximately 42 days. We assessed COVID-19 symptoms and collected specimens. Oropharyngeal (OP), anterior nasal (AN), and saliva (SA) specimens were tested for the presence of SARS-CoV-2 RNA, using RT-PCR, and sent for viral culture. Serology, including neutralizing antibodies, was measured in blood specimens.

Results

Fifteen participants, with a median age of 58 (range, 37‒77) years, were enrolled. Median duration of RT-PCR positivity from diagnosis was 18 days (interquartile range [IQR], 8‒24 days). Ten participants had at least one, for a total of 41, positive RT-PCR specimens ≥10 days after symptoms onset. Of these 41 specimens, 21 underwent viral culture; one (5%) was positive 14 days after symptom onset. Thirteen participants developed SARS-CoV-2-specific antibodies, 11 of which included neutralizing antibodies. RT-PCRs remained positive after seroconversion in eight participants and after detection of neutralizing antibodies in four participants; however, all of these samples were culture negative.

Conclusions

Patients with ESKD on maintenance dialysis remained persistently and intermittently SARS-CoV-2-RT-PCR positive. However, of the 15 participants, only one had infectious virus, on day 14 after symptom onset. Most participants mounted an antibody response, including neutralizing antibodies. Participants continued having RT-PCR-positive results in the presence of SARS-CoV-2-specific antibodies, but without replication-competent virus detected.

Saliva-Based ELISAs for Effective SARS-CoV-2 Antibody Monitoring in Vaccinated Individuals

In March 2020, the World Health Organization (WHO) declared a global health emergency-the coronavirus disease 2019 (COVID-19) pandemic. Since then, the development and implementation of vaccines against the virus amidst emerging cases of re-infection has prompted researchers to work towards understanding how immunity develops and is sustained. Serological testing has been instrumental in monitoring the development and persistence of antibodies against SARS-CoV-2 infection, however inconsistencies in detection have been reported by different methods. As serological testing becomes more commonplace, it is important to establish widespread and repeatable processes for monitoring vaccine efficacy. Therefore, we present enzyme linked immunosorbent assays (ELISAs) compatible for antibody detection in saliva as highly accurate, efficacious, and scalable tools for studying the immune response in individuals vaccinated against SARS-CoV-2.

Immunological assessment of SARS-CoV-2 infection in pregnancy from diagnosis to delivery: A multicentre prospective study

BACKGROUND

Background Population-based data on SARS-CoV-2 infection in pregnancy and assessment of passive immunity to the neonate, is lacking. We profiled the maternal and fetal response using a combination of viral RNA from naso-pharyngeal swabs and serological assessment of antibodies against SARS-CoV-2.

METHODS

This multicentre prospective observational study was conducted between March 24th and August 31st 2020. Two independent cohorts were established, a symptomatic SARS-CoV-2 cohort and a cohort of asymptomatic pregnant women attending two of the largest maternity hospitals in Europe. Symptomatic women were invited to provide a serum sample to assess antibody responses. Asymptomatic pregnant women provided a nasopharyngeal swab and serum sample. RT-PCR for viral RNA was performed using the Cobas SARS-CoV-2 6800 platform (Roche). Umbilical cord bloods were obtained at delivery. Maternal and fetal serological response was measured using both the Elecsys® Anti-SARS-CoV-2 immunoassay (Roche), Abbott SARS-CoV-2 IgG Assay and the IgM Architect assay. Informed written consent was obtained from all participants.

RESULTS

Ten of twenty three symptomatic women had SARS-CoV-2 RNA detected on nasopharyngeal swabs. Five (5/23, 21.7%) demonstrated serological evidence of anti-SARS-CoV-2 IgG antibodies and seven (30.4%, 7/23) were positive for IgM antibodies. In the asymptomatic cohort, the prevalence of SARS-CoV-2 infection in RNA was 0.16% (1/608). IgG SARS-CoV-2 antibodies were detected in 1·67% (10/598, 95% CI 0·8%-3·1%) and IgM in 3·51% (21/598, 95% CI 2·3-5·5%). Nine women had repeat testing post the baseline test. Four (4/9, 44%) remained IgM positive and one remained IgG positive. 3 IgG anti-SARS-CoV-2 antibodies were detectable in cord bloods from babies born to five seropositive women who delivered during the study. The mean gestation at serological test was 34 weeks. The mean time between maternal serologic positivity and detection in umbilical cord samples was 28 days.

CONCLUSION

Using two independent serological assays, we present a comprehensive illustration of the antibody response to SARS-CoV-2 in pregnancy, and show a low prevalence of asymptomatic SARS-CoV2. Transplacental migration of anti-SARS-CoV-2 antibodies was identified in cord blood of women who demonstrated antenatal anti-SARS-CoV-2 antibodies, raising the possibility of passive immunity.

Association of HLA genotypes, AB0 blood type and chemokine receptor 5 mutant CD195 with the clinical course of COVID-19

BACKGROUND

COVID-19, the pandemic disease caused by infection with SARS-CoV-2, may take highly variable clinical courses, ranging from symptom-free and pauci-symptomatic to fatal disease. The goal of the current study was to assess the association of COVID-19 clinical courses controlled by patients' adaptive immune responses without progression to severe disease with patients' Human Leukocyte Antigen (HLA) genetics, AB0 blood group antigens, and the presence or absence of near-loss-of-function delta 32 deletion mutant of the C-C chemokine receptor type 5 (CCR5).

PATIENT AND METHODS

An exploratory observational study including 157 adult COVID-19 convalescent patients was performed with a median follow-up of 250 days. The impact of different HLA genotypes, AB0 blood group antigens, and the CCR5 mutant CD195 were investigated for their role in the clinical course of COVID-19. In addition, this study addressed levels of severity and morbidity of COVID-19. The association of the immunogenetic background parameters were further related to patients' humoral antiviral immune response patterns by longitudinal observation.

RESULTS

Univariate HLA analyses identified putatively protective HLA alleles (HLA class II DRB1*01:01 and HLA class I B*35:01, with a trend for DRB1*03:01). They were associated with reduced durations of disease instead decreased (rather than increased) total anti-S IgG levels. They had a higher virus neutralizing capacity compared to non-carriers. Conversely, analyses also identified HLA alleles (HLA class II DQB1*03:02 und HLA class I B*15:01) not associated with such benefit in the patient cohort of this study. Hierarchical testing by Cox regression analyses confirmed the significance of the protective effect of the HLA alleles identified (when assessed in composite) in terms of disease duration, whereas AB0 blood group antigen heterozygosity was found to be significantly associated with disease severity (rather than duration) in our cohort. A suggestive association of a heterozygous CCR5 delta 32 mutation status with prolonged disease duration was implied by univariate analyses but could not be confirmed by hierarchical multivariate testing.

CONCLUSION

The current study shows that the presence of HLA class II DRB1*01:01 and HLA class I B*35:01 is of even stronger association with reduced disease duration in mild and moderate COVID-19 than age or any other potential risk factor assessed. Prospective studies in larger patient populations also including novel SARS-CoV-2 variants will be required to assess the impact of HLA genetics on the capacity of mounting protective vaccination responses in the future.

Immunology of SARS-CoV-2 infections and vaccines

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections trigger viral RNA sensors such as TLR7 and RIG-I, thereby leading to production of type I interferon (IFN) and other inflammatory mediators. Expression of viral proteins in the context of this inflammation leads to stereotypical antigen-specific antibody and T cell responses that clear the virus. Immunity is then maintained through long-lived antibody-secreting plasma cells and by memory B and T cells that can initiate anamnestic responses. Each of these steps is consistent with prior knowledge of acute RNA virus infections. Yet there are certain concepts, while not entirely new, that have been resurrected by the biology of severe SARS-CoV-2 infections and deserve further attention. These include production of anti-IFN autoantibodies, early inflammatory processes that slow adaptive humoral immunity, immunodominance of antibody responses, and original antigenic sin. Moreover, multiple different vaccine platforms allow for comparisons of pathways that promote robust and durable adaptive immunity.

Mechanism of a COVID-19 nanoparticle vaccine candidate that elicits a broadly neutralizing antibody response to SARS-CoV-2 variants

Vaccines that induce potent neutralizing antibody (NAb) responses against emerging variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are essential for combating the coronavirus disease 2019 (COVID-19) pandemic. We demonstrated that mouse plasma induced by self-assembling protein nanoparticles (SApNPs) that present 20 rationally designed S2GΔHR2 spikes of the ancestral Wuhan-Hu-1 strain can neutralize the B.1.1.7, B.1.351, P.1, and B.1.617 variants with the same potency. The adjuvant effect on vaccine-induced immunity was investigated by testing 16 formulations for the multilayered I3-01v9 SApNP. Using single-cell sorting, monoclonal antibodies (mAbs) with diverse neutralization breadth and potency were isolated from mice immunized with the receptor binding domain (RBD), S2GΔHR2 spike, and SApNP vaccines. The mechanism of vaccine-induced immunity was examined in mice. Compared with the soluble spike, the I3-01v9 SApNP showed 6-fold longer retention, 4-fold greater presentation on follicular dendritic cell dendrites, and 5-fold stronger germinal center reactions in lymph node follicles.

Antibody Response against SARS-CoV-2 Infection: Implications for Diagnosis, Treatment and Vaccine Development

Many recent studies have reported the onset of a robust antibody response to SARS-CoV-2 infection and highlighted produced antibodies' specific qualitative and quantitative aspects, relevant for developing antibody-based diagnostic and therapeutic options. In this review, firstly we will report main information acquired so far regarding the humoral response to COVID-19; we will concentrate, in particular, upon the observed levels and the kinetics, the specificity spectrum and the neutralizing potential of antibodies produced in infected patients. We will then discuss the implication of humoral response's characteristics in the development and correct use of serologic tests, as well as the efficacy and safety of convalescent plasma therapy and of neutralizing monoclonal antibodies for treating infected patients and preventing new infections. An update of the list of newly isolated specific neutralizing antibodies and suggestions for vaccine evaluation and development will be also provided.

Neutralizing antibody response to SARS-CoV-2 persists 9 months post symptom onset in mild and asymptomatic patients

Objective

A better understanding of the immune response against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection is critical to predict its dynamics within the general population and its impact on the vaccination strategy. This study assessed the persistence of neutralizing antibody (Nab) activity and SARS-CoV-2 serology in serum samples of mild and asymptomatic patients 9 months post symptom onset (PSO) in a primary care context among immunocompetent adults.

Methods

A longitudinal cohort of crew members (CMs) exposed to coronavirus disease 2019 (COVID-19) during an outbreak of SARS-CoV-2 on the French aircraft carrier ‘Charles de Gaulle’ in April 2020 was created. CMs infected with COVID-19 and with positive serology at the end of quarantine were tested 9 months PSO. Samples were collected 18 and 280 days PSO. For each patient, both serology and serum viral neutralizing activity were performed.

Results

In total, 86 CMs were analysed. Samples were collected 18 and 280 days PSO. The seroconversion rates were 100% and 93% (82/86) at 18 and 280 days PSO, respectively, and 72.7% of patients exhibited persistent Nab activity at 9 months, regardless of disease severity.

Conclusion

Nab activity persists for up to 9 months following asymptomatic/mild COVID-19 among young adults, regardless of serological results.

Asymptomatic or mild symptomatic SARS-CoV-2 infection elicits durable neutralizing antibody responses in children and adolescents

As SARS-CoV-2 continues to spread globally, questions have emerged regarding the strength and durability of immune responses in specific populations. In this study, we evaluated humoral immune responses in 69 children and adolescents with asymptomatic or mild symptomatic SARS-CoV-2 infection. We detected robust IgM, IgG, and IgA antibody responses to a broad array of SARS-CoV-2 antigens at the time of acute infection and 2 and 4 months after acute infection in all participants. Notably, these antibody responses were associated with virus-neutralizing activity that was still detectable 4 months after acute infection in 94% of children. Moreover, antibody responses and neutralizing activity in sera from children and adolescents were comparable or superior to those observed in sera from 24 adults with mild symptomatic infection. Taken together, these findings indicate that children and adolescents with mild or asymptomatic SARS-CoV-2 infection generate robust and durable humoral immune responses that can likely contribute to protection from reinfection.

Pre-Vaccine Positivity of SARS-CoV-2 Antibodies in Alberta, Canada during the First Two Waves of the COVID-19 Pandemic

We systematically evaluated SARS-CoV-2 IgG positivity in a provincial cohort to understand the local epidemiology of COVID-19 and support evidence-based public health decisions. Residual blood samples were collected for serology testing over 5-day periods monthly from June 2020 to January 2021 from six clinical laboratories across the province of Alberta, Canada. A total of 93,993 individual patient samples were tested with a SARS-CoV-2 nucleocapsid antibody assay with positives confirmed using a spike antibody assay. Population-adjusted SARS-CoV-2 IgG seropositivity was 0.92% (95% confidence interval [CI]: 0.91 to 0.93%) shortly after the first COVID-19 wave in June 2020, increasing to 4.63% (95% CI: 4.61 to 4.65%) amid the second wave in January 2021. There was no significant difference in seropositivity between males and females (1.39% versus 1.27%; P = 0.11). Ages with highest seropositivity were 0 to 9 years (2.71%, 95% CI: 1.64 to 3.78%) followed by 20 to 29 years (1.58%, 95% CI: 1.12 to 2.04%), with the lowest rates seen in those aged 70 to 79 (0.79%, 95% CI: 0.65 to 0.93%) and >80 (0.78%, 95% CI: 0.60 to 0.97%). Compared to the seronegative group, seropositive patients inhabited geographic areas with lower household income ($87,500 versus $97,500; P < 0.001), larger household sizes, and higher proportions of people with education levels of secondary school or lower, as well as immigrants and visible minority groups (all P < 0.05). A total of 53.7% of seropositive individuals were potentially undetected cases with no prior positive COVID-19 nucleic acid test (NAAT). Antibodies were detectable in some patients up to 9 months post positive NAAT result. This seroprevalence study will continue to inform public health decisions by identifying at-risk demographics and geographical areas. IMPORTANCE Using SARS-CoV-2 serology testing, we assessed the proportion of people in Alberta, Canada (population 4.4 million) positive for COVID-19 antibodies, indicating previous infection, during the first two waves of the COVID-19 pandemic (prior to vaccination programs). Linking these results with sociodemographic population data provides valuable information as to which groups of the population are more likely to have been infected with the SARS-CoV-2 virus to help facilitate public health decision-making and interventions. We also compared seropositivity data with previous COVID-19 molecular testing results. Absence of antibody and molecular testing were highly correlated (95% negative concordance). Positive antibody correlation with a previous positive molecular test was low, suggesting the possibility of mild/asymptomatic infection or other reasons leading individuals from seeking medical attention. Our data highlight that the true estimate of population prevalence of COVID-19 is likely best informed by combining data from both serology and molecular testing.

Risk Factors for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection and Presence of Anti-SARS-CoV-2 Antibodies Among University Student Dormitory Residents, September-November 2020

BACKGROUND

Multiple severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreaks occurred at universities during Fall 2020, but little is known about risk factors for campus-associated infections or immunity provided by anti-SARS-CoV-2 antibodies in young adults.

METHODS

We conducted surveys and serology tests among students living in dormitories in September and November to examine infection risk factors and antibody presence. Using campus weekly reverse-transcription polymerase chain reaction (RT-PCR) test results, the relationship between survey responses, SARS-CoV-2 antibodies, and infections was assessed.

RESULTS

Of 6136 students, 1197 completed the survey and 572 also completed serologic testing in September compared with 517 and 414 in November, respectively. Participation in fraternity or sorority events (adjusted risk ratio [aRR], 1.9 [95% confidence interval {CI}, 1.4-2.5]) and frequent alcohol consumption (aRR, 1.6 [95% CI, 1.2-2.2]) were associated with SARS-CoV-2 infection. Mask wearing during social events (aRR, 0.6 [95% CI, .6-1.0]) was associated with decreased risk. None of the 20 students with antibodies in September tested positive for SARS-CoV-2 during the semester, while 27.8% of students who tested RT-PCR positive tested negative for antibodies in November.

CONCLUSIONS

Frequent drinking and attending social events were associated with SARS-CoV-2 infection. Antibody presence in September appeared to be protective from reinfection, but this finding was not statistically significant.

The COVID-19 Menace

Coronavirus disease 2019 (COVID-19) is caused by the new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which binds to ectoenzyme angiotensin-converting enzyme 2. It is very contagious and is spreading rapidly around the world. Until now, coronaviruses have mainly been associated with the aerodigestive tract due to the presence of a monobasic cleavage site for the resident transmembrane serine protease 2. Notably, SARS-CoV-2 is equipped with a second, polybasic cleavage site for the ubiquitous furin protease, which may determine the widespread tissue tropism. Furthermore, the terminal sequence of the furin-cleaved spike protein also binds to neuropilin receptors. Clinically, there is enormous variability in the severity of the disease. Severe consequences are seen in a relatively small number of patients, most show moderate symptoms, but asymptomatic cases, especially among young people, drive disease spread. Unfortunately, the number of local infections can quickly build up, causing disease outbreaks suddenly exhausting health services' capacity. Therefore, COVID-19 is dangerous and unpredictable and has become the most serious threat for generations. Here, the latest research on COVID-19 is summarized, including its spread, testing methods, organ-specific complications, the role of comorbidities, long-term consequences, mortality, as well as a new hope for immunity, drugs, and vaccines.

COVID-19 reinfection in a patient with a serious mental illness within a long-term inpatient psychiatric care hospital

There is an increasing number of case reports of COVID-19 reinfection. The mechanism of reinfection is poorly understood and evolving. Prevention of the transmission of severe acute respiratory syndrome coronavirus 2 for those with a serious mental illness (SMI) living in a congregate setting presents unique challenges. In this case report, we describe an individual with an SMI in a long-term inpatient psychiatric care hospital who was initially diagnosed in June 2020 with COVID-19 infection via a polymerase chain reaction test. Approximately 6 months later, the patient presented with a COVID-19 reinfection and more severe COVID-like symptoms.

TOP-Plus Is a Versatile Biosensor Platform for Monitoring SARS-CoV-2 Antibody Durability

BACKGROUND

Low initial severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody titers dropping to undetectable levels within months after infection have raised concerns about long-term immunity. Both the antibody levels and the avidity of the antibody-antigen interaction should be examined to understand the quality of the antibody response.

METHODS

A testing-on-a-probe "plus" panel (TOP-Plus) was developed to include a newly developed avidity assay built into the previously described SARS-CoV-2 TOP assays that measured total antibody (TAb), surrogate neutralizing antibody (SNAb), IgM, and IgG on a versatile biosensor platform. TAb and SNAb levels were compared with avidity in previously infected individuals at 1.3 and 6.2 months after infection in paired samples from 80 patients with coronavirus disease 2019 (COVID-19). Sera from individuals vaccinated for SARS-CoV-2 were also evaluated for antibody avidity.

RESULTS

The newly designed avidity assay in this TOP panel correlated well with a reference Bio-Layer Interferometry avidity assay (r = 0.88). The imprecision of the TOP avidity assay was <10%. Although TAb and neutralization activity (by SNAb) decreased between 1.3 and 6.2 months after infection, the antibody avidity increased significantly (P < 0.0001). Antibody avidity in 10 SARS-CoV-2 vaccinated individuals (median: 28 days after vaccination) was comparable to the measured antibody avidity in infected individuals (median: 26 days after infection).

CONCLUSIONS

This highly precise and versatile TOP-Plus panel with the ability to measure SARS-CoV-2 TAb, SNAb, IgG, and IgM antibody levels and avidity of individual sera on one sensor can become a valuable asset in monitoring not only patients infected with SARS-CoV-2 but also the status of individuals' COVID-19 vaccination response.

SARS-CoV-2 reinfection in patients negative for immunoglobulin G following recovery from COVID-19

While many patients infected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) eventually produce neutralising antibodies, the degree of susceptibility of previously infected individuals to reinfection by SARS-CoV-2 is currently unknown. To better understand the impact of the immunoglobulin (IgG) level on reinfection in recovered coronavirus disease 2019 (COVID-19) patients, anti-nucleocapsid IgG levels against SARS-CoV-2 were measured in 829 patients with a previously confirmed infection just after their recovery. Notably, 87 of these patients had no detectable IgG concentration. While there was just one case of asymptomatic reinfection 4.5 months after the initial recovery amongst patients with detectable anti-nucleocapsid IgG levels, 25 of the 87 patients negative for anti-nucleocapsid IgG were reinfected within one to three months after their first infection. Therefore, patients who recover from COVID-19 with no detectable anti-nucleocapsid IgG concentration appear to remain more susceptible to reinfection by SARS-CoV-2, with no apparent immunity. Also, although our results suggest the chance is lower, the possibility for recovered patients with positive anti-nucleocapsid IgG findings to be reinfected similarly exists.

Recent progress on the mutations of SARS-CoV-2 spike protein and suggestions for prevention and controlling of the pandemic

Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) infection has caused a global pandemic in the past year, which poses continuing threat to human beings. To date, more than 3561 mutations in the viral spike protein were identified, including 2434 mutations that cause amino acid changes with 343 amino acids located in the viral receptor-binding domain (RBD). Among these mutations, the most representative ones are substitution mutations such as D614G, N501Y, Y453F, N439K/R, P681H, K417N/T, and E484K, and deletion mutations of ΔH69/V70 and Δ242-244, which confer the virus with enhanced infectivity, transmissibility, and resistance to neutralization. In this review, we discussed the recent findings of SARS-CoV-2 for highlighting mutations and variants on virus transmissibility and pathogenicity. Moreover, several suggestions for prevention and controlling the pandemic are also proposed.

Levels of SARS-CoV-2 population exposure are considerably higher than suggested by seroprevalence surveys

Accurate knowledge of prior population exposure has critical ramifications for preparedness plans for future SARS-CoV-2 epidemic waves and vaccine prioritization strategies. Serological studies can be used to estimate levels of past exposure and thus position populations in their epidemic timeline. To circumvent biases introduced by the decay in antibody titers over time, methods for estimating population exposure should account for seroreversion, to reflect that changes in seroprevalence measures over time are the net effect of increases due to recent transmission and decreases due to antibody waning. Here, we present a new method that combines multiple datasets (serology, mortality, and virus positivity ratios) to estimate seroreversion time and infection fatality ratios (IFR) and simultaneously infer population exposure levels. The results indicate that the average time to seroreversion is around six months, IFR is 0.54% to 1.3%, and true exposure may be more than double the current seroprevalence levels reported for several regions of England.

Understanding neutralising antibodies against SARS-CoV-2 and their implications in clinical practice

SARS-CoV-2 is a newly identified member of the coronavirus family that has caused the Coronavirus disease 2019 (COVID-19) pandemic. This rapidly evolving and unrelenting SARS-CoV-2 has disrupted the lives and livelihoods of millions worldwide. As of 23 August 2021, a total of 211,373,303 COVID-19 cases have been confirmed globally with a death toll of 4,424,341. A strong understanding of the infection pathway of SARS-CoV-2, and how our immune system responds to the virus is highly pertinent for guiding the development and improvement of effective treatments. In this review, we discuss the current understanding of neutralising antibodies (NAbs) and their implications in clinical practice. The aspects include the pathophysiology of the immune response, particularly humoral adaptive immunity and the roles of NAbs from B cells in infection clearance. We summarise the onset and persistence of IgA, IgM and IgG antibodies, and we explore their roles in neutralising SARS-CoV-2, their persistence in convalescent individuals, and in reinfection. Furthermore, we also review the applications of neutralising antibodies in the clinical setting-from predictors of disease severity to serological testing to vaccinations, and finally in therapeutics such as convalescent plasma infusion.

Evolution of antibody responses up to 13 months after SARS-CoV-2 infection and risk of reinfection

Background

Assessment of the kinetics of SARS-CoV-2 antibodies is essential in predicting risk of reinfection and durability of vaccine protection.

Methods

This is a prospective, monocentric, longitudinal, cohort clinical study. Healthcare workers (HCW) from Strasbourg University Hospital were enrolled between April 6th and May 7th, 2020 and followed up to 422 days. Serial serum samples were tested for antibodies against the Receptor Binding Domain (RBD) of the spike protein and nucleocapsid protein (N) to characterize the kinetics of SARS-CoV-2 antibodies and the incidence of reinfection. Live-neutralization assays were performed for a subset of samples before and after vaccination to analyze sensitivity to SARS-CoV-2 variants.

Findings

A total of 4290 samples from 393 convalescent COVID-19 and 916 COVID-19 negative individuals were analyzed. In convalescent individuals, SARS-CoV-2 antibodies followed a triphasic kinetic model with half-lives at month (M) 11–13 of 283 days (95% CI 231–349) for anti-N and 725 days (95% CI 623–921) for anti-RBD IgG, which stabilized at a median of 1.54 log BAU/mL (95% CI 1.42–1.67). The incidence of SARS-CoV-2 infections was 12.22 and 0.40 per 100 person-years in COVID-19-negative and COVID-19-positive HCW, respectively, indicating a relative reduction in the incidence of SARS-CoV-2 reinfection of 96.7%. Live-virus neutralization assay revealed that after one year, variants D614G and B.1.1.7, but less so B.1.351, were sensitive to anti-RBD antibodies at 1.4 log BAU/mL, while IgG ≥ 2.0 log BAU/mL strongly neutralized all three variants. These latter anti-RBD IgG titers were reached by all vaccinated HCW regardless of pre-vaccination IgG levels and type of vaccine.

Interpretation

Our study demonstrates a long-term persistence of anti-RBD antibodies that may reduce risk of reinfection. By significantly increasing cross-neutralizing antibody titers, a single-dose vaccination strengthens protection against variants.

Fun1ding

None.

Humoral response to spike S1 and S2 and nucleocapsid proteins on microarray after SARS-CoV-2 infection

Many aspects of the humoral immune response to severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), such as its role in protection after natural infection, are still unclear. We evaluated IgA and IgG response to spike subunits 1 and 2 (S1 and S2) and Nucleocapsid proteins of SARS‐COV‐2 in serum samples of 109 volunteers with viral RNA detected or seroconversion with different clinical evolution (asymptomatic, mild, moderate, and severe coronavirus disease 2019), using the ViraChip® Test Kit. We observed that the quantification of antibodies to all antigens had a positive correlation to disease severity, which was strongly associated with the presence of comorbidities. Seroreversion was not uncommon even during the short (median of 77 days) observation, occurring in 15% of mild‐asymptomatic cases at a median of 55 days for IgG and 46 days for IgA. The time to reach the maximal antibody response did not differ significantly among recovered and deceased volunteers. Our study illustrated the dynamic of anti‐S1, anti‐N, and anti‐S2 IgA and IgG antibodies, and suggests that high production of IgG and IgA does not guarantee protection to disease severity and that functional responses that have been studied by other groups, such as antibody avidity, need further attention.

Symptomatic SARS‐CoV‐2 infection generally elicits strong humoral immune response.

IgA and IgG titers to three viral antigens (S1, S2 and N) correlate to severity of COVID‐19 disease.

Seroreversion is not uncommon and may occur few months after SARS‐CoV‐2 infection.

Elucidation of functional characteristics of antibodies are necessary to better understand disease pathogenesis and may guide vaccine boosting strategies.

A framework for monitoring population immunity to SARS-CoV-2

In the effort to control SARS-CoV-2 transmission, public health agencies in the United States and globally are aiming to increase population immunity. Immunity through vaccination and acquired following recovery from natural infection are the two means to build up population immunity, with vaccination being the safe pathway. However, measuring the contribution to population immunity from vaccination or natural infection is non-trivial. Historical COVID-19 case counts and vaccine coverage are necessary information but are not sufficient to approximate population immunity. Here, we consider the nuances of measuring each and propose an analytical framework for integrating the necessary data on cumulative vaccinations and natural infections at the state and national level. To guide vaccine roll-out and other aspects of control over the coming months, we recommend analytics that combine vaccine coverage with local (e.g. county-level) history of case reports and adjustment for waning antibodies to establish local estimates of population immunity. To do so, the strategic use of minimally-biased serology surveys integrated with vaccine administration data can improve estimates of the aggregate level of immunity to guide data-driven decisions to re-open safely and prioritize vaccination efforts.

[SARS-CoV-2 vaccines and reaction of the immune system. Can the epidemic spread of the virus be prevented by vaccination?]

Since the end of 2019 a new coronavirus, SARS-CoV-2, first identified in Wuhan, China, is spreading around the world partially associated with a high death toll. Besides hygienic measurements to reduce the spread of the virus vaccines have been confected, partially based on the experiences with Ebola virus vaccine, based on recombinant human or chimpanzee adenovirus carrying the spike protein and its ACE2 receptor binding domain (RBD). Further vaccines are constructed by spike protein coding mRNA incorporated in lipid nano vesicles that after entry in human cells produce spike protein. Both vaccine types induce a strong immune response that lasts for months possibly for T-cell immunity a few years. Due to mutations in the coronavirus genome in several parts of the world variants selected, that were partially more pathogenic and partially easier transmissible - variants of concern (VOC). Until now vaccinees are protected against the VOC, even when protection might be reduced compared to the Wuhan wild virus.An open field is still how long the vaccine induced immunity will be sufficient to prevent infection and/or disease; and how long the time period will last until revaccination will be required for life saving protection, whether a third vaccination is needed, and whether revaccination with an adenovirus-based vaccine will be tolerated.

Large-scale study of antibody titer decay following BNT162b2 mRNA vaccine or SARS-CoV-2 infection

BACKGROUND

Immune protection following either vaccination or infection with SARS-CoV-2 decreases over time.

OBJECTIVE

To determine the kinetics of SARS-CoV-2 IgG antibodies following administration of two doses of BNT162b2 vaccine, or SARS-CoV-2 infection in unvaccinated individuals.

METHODS

Antibody titers were measured between January 31, 2021, and July 31, 2021 in two mutually exclusive groups: i) vaccinated individuals who received two doses of BNT162b2 vaccine and had no history of previous infection with COVID-19 and ii) SARS-CoV-2 convalescents who had not received the vaccine.

RESULTS

A total of 2,653 individuals fully vaccinated by two doses of vaccine during the study period and 4,361 convalescent patients were included. Higher SARS-CoV-2 IgG antibody titers were observed in vaccinated individuals (median 1581 AU/mL IQR [533.8-5644.6]) after the second vaccination, than in convalescent individuals (median 355.3 AU/mL IQR [141.2-998.7]; p<0.001). In vaccinated subjects, antibody titers decreased by up to 40% each subsequent month while in convalescents they decreased by less than 5% per month. Six months after BNT162b2 vaccination 16.1% subjects had antibody levels below the seropositivity threshold of <50 AU/mL, while only 10.8% of convalescent patients were below <50 AU/mL threshold after 9 months from SARS-CoV-2 infection.

CONCLUSIONS

This study demonstrates individuals who received the Pfizer-BioNTech mRNA vaccine have different kinetics of antibody levels compared to patients who had been infected with the SARS-CoV-2 virus, with higher initial levels but a much faster exponential decrease in the first group.

FUNDING

This research was internally funded by Leumit Health Services (LHS) and was supported in part by the Intramural Research Program, National Institutes of Health, National Cancer Institute, Center for Cancer Research.The content of this publication does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.

IMPACT STATEMENT

Large scale study display the kinetics of SARS-CoV-2 IgG antibodies present in individuals vaccinated with two doses of mRNA vaccine vs. unvaccinated patients who had recovered from the disease: initial levels of antibody are much higher in vaccinated patients, but decrease faster.

Longitudinal analysis of antibody decay in convalescent COVID-19 patients

Determining the sustainability of antibodies targeting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is essential for predicting immune response against the Coronavirus disease 2019 (COVID-19). To quantify the antibody decay rates among the varying levels of anti-nucleocapsid (anti-N) Immunoglobulin G (IgG) in convalescent COVID-19 patients and estimate the length of time they maintained SARS-CoV-2 specific antibodies, we have collected longitudinal blood samples from 943 patients over the course of seven months after their initial detection of SARS-CoV-2 virus by RT-PCR. Anti-N IgG levels were then quantified in these blood samples. The primary study outcome was the comparison of antibody decay rates from convalescent patients with high or low initial levels of antibodies using a mixed linear model. Additional measures include the length of time that patients maintain sustainable levels of anti-N IgG. Antibody quantification of blood samples donated by the same subject multiple times shows a gradual decrease of IgG levels to the cutoff index level of 1.4 signal/cut-off (S/C) on the Abbott Architect SARS-CoV-2 IgG test. In addition, this study shows that antibody reduction rate is dependent on initial IgG levels, and patients with initial IgG levels above 3 S/C show a significant 1.68-fold faster reduction rate compared to those with initial IgG levels below 3 S/C. For a majority of the donors naturally occurring anti-N antibodies were detected above the threshold for only four months after infection with SARS-CoV-2. This study is clinically important for the prediction of immune response capacity in COVID-19 patients.

Immune response to SARS-CoV-2 in children: A review of the current knowledge

Host immune responses to severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), especially in children, are still under investigation. Children with coronavirus disease 2019 (COVID‐19) constitute a significant study group of immune responses as they rarely present with severe clinical manifestations, require hospitalization, or develop complications such as multisystem inflammatory syndrome in children (MIS‐C) associated with SARS‐CoV‐2 infection. The deciphering of children’s immune responses during COVID‐19 infection will provide information about the protective mechanisms, while new potential targets for future therapies are likely to be revealed. Despite the limited immunological studies in children with COVID‐19, this review compares data between adults and children in terms of innate and adaptive immunity to SARS‐CoV‐2, discusses the possible reasons why children are mostly asymptomatic, and highlights unanswered or unclear immunological issues. Current evidence suggests that the activity of innate immunity seems to be crucial to the early phases of SARS‐CoV‐2 infection and adaptive memory immunity is vital to prevent reinfection.

Despite the limited immunological studies from children with COVID‐19, this review compares data between adults and children in terms of innate and adaptive immunity to SARS‐CoV‐2, discusses the possible reasons why children are mostly asymptomatic, and highlights unanswered or unclear immunological issues.

Significance of SARS-CoV-2 specific antibody testing during COVID-19 vaccine allocation

OBJECTIVE

To assess the value of using SARS-CoV-2 specific antibody testing to prioritize the vaccination of susceptible individuals as part of a COVID-19 vaccine distribution plan when vaccine supply is limited.

METHODS

An extended susceptible-infected-recovered (SIR) compartmental model was used to simulate COVID-19 spread when considering diagnosis, isolation, and vaccination of a cohort of 1 million individuals. The scenarios modeled represented 4 pandemic severity scenarios and various times when the vaccine becomes available during the pandemic. Eligible individuals have a probability p of receiving antibody testing prior to vaccination (p = 0, 0.25, 0.5, 0.75, and 1). The vaccine was modeled as a single dose vaccine with 90% and 70% efficacy. The value of serology testing was evaluated by comparing the infection attack rate, peak infections, peak day, and deaths.

RESULTS

The use of antibody testing to prioritize the allocation of limited vaccines reduces infection attack rates and deaths. The size of the reduction depends on when the vaccine becomes available relative to the infection peak day. The largest percentage reduction in cases and deaths occurs when the vaccine is deployed before and close to the infection peak day. The reduction in the number of cases and deaths diminishes as vaccine deployment is delayed.

CONCLUSIONS

Antibody testing as part of the vaccination plan is an effective method to maximize the benefit of a COVID-19 vaccine. Decision-makers need to consider relative timing between the infection peak day and when the vaccine becomes available.

Antibody Responses to Natural SARS-CoV-2 Infection or after COVID-19 Vaccination

The novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is the causative agent of the ongoing pandemic of coronavirus disease 2019 (COVID-19). The clinical severity of COVID-19 ranges from asymptomatic to critical disease and, eventually, death in smaller subsets of patients. The first case of COVID-19 was declared at the end of 2019 and it has since spread worldwide and remained a challenge in 2021, with the emergence of variants of concern. In fact, new concerns were the still unclear situation of SARS-CoV-2 immunity during the ongoing pandemic and progress with vaccination. If maintained at sufficiently high levels, the immune response could effectively block reinfection, which might confer long-lived protection. Understanding the protective capacity and the duration of humoral immunity during SARS-CoV-2 infection or after vaccination is critical for managing the pandemic and would also provide more evidence about the efficacy of SARS-CoV-2 vaccines. However, the exact features of antibody responses that govern SARS-CoV-2 infection or after vaccination remain unclear. This review summarizes the main knowledge that we have about the humoral immune response during COVID-19 disease or after vaccination. Such knowledge should help to optimize vaccination strategies and public health decisions.

The fall in antibody response to SARS-CoV-2: a longitudinal study of asymptomatic to critically ill patients up to 10 months after recovery

The aim of this study was to assess the long-term dynamics and factors associated with the serological response against the severe acute respiratory syndrome coronavirus 2 after primary infection. A prospective longitudinal study was conducted with monthly serological follow-up during the first 4 months, and then at 6, 8, and 10 months after the disease onset of all recovered adult in- and outpatients with coronavirus disease 2019 (COVID-19) attending Udine Hospital (Italy) during the first wave (from March to May 2020). A total of 546 individuals were included (289 female, mean age 53.1 years), mostly with mild COVID-19 (370, 68.3%). Patients were followed for a median of 302 days (interquartile range, 186 to 311). The overall seroconversion rate within 2 months was 32% for IgM and 90% for IgG. Seroreversion was observed in 90% of patients for IgM at 4 months and in 47% for IgG at 10 months. Older age, number of symptoms at acute onset, and severity of acute COVID-19 were all independent predictors of long-term immunity both for IgM (β, linear regression coefficient, 1.10, P = 0.001; β 5.15 P = 0.014; β 43.84 P = 0.021, respectively) and for IgG (β 1.43 P < 0.001; β 10.46 P < 0.001; β 46.79 P < 0.001, respectively), whereas the initial IgG peak was associated only with IgG duration (β 1.12, P < 0.001). IgM antibodies disappeared at 4 months, and IgG antibodies declined in about half of patients 10 months after acute COVID-19. These effects varied depending on the intensity of the initial antibody response, age, and burden of acute COVID-19.

Longitudinal analysis to characterize classes and subclasses of antibody responses to recombinant receptor-binding protein (RBD) of SARS-CoV-2 in COVID-19 patients in Thailand

Serological assays to detect antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) might contribute to confirming the suspected coronavirus disease 2019 (COVID-19) in patients not detected with molecular assays. Human antibodies that target the host angiotensin-converting enzyme 2-binding domain of the viral spike protein are a target for serodiagnosis and therapeutics. This study aimed to characterize the classes and subclasses of antibody responses to a recombinant receptor-binding protein (RBD) of SARS-CoV-2 in COVID-19 patients and investigated the reactivity of these antibodies in patients with other tropical infections and healthy individuals in Thailand. ELISAs for IgM, IgA, IgG and IgG subclasses based on RBD antigen were developed and tested with time series of 27 serum samples from 15 patients with COVID-19 and 60 samples from pre-COVID-19 outbreaks including acute dengue fever, murine typhus, influenza, leptospirosis and healthy individuals. Both RBD-specific IgA and IgG were detected in only 21% of the COVID-19 patients in the acute phase. The median IgA and IgG levels were significantly higher in the convalescent serum sample compared to the acute serum sample (P < 0.05). We observed the highest correlation between levels of IgG and IgA (rho = 0. 92). IgG1 and IgG3 were the major IgG subclasses detected in SARS-CoV-2 infection. Only acute IgG3 level was negatively associated with viral detection based on RT-PCR of ORF1ab gene (rho = -0.57). The median IgA and IgG levels in convalescence sera of COVID-19 patients were significantly higher than healthy individuals and convalescent sera of other febrile infectious patients. The analyses of antibody classes and subclasses provide insights into human immune responses against SARS-CoV-2 during natural infection and interpretation of antibody assays.

Evidence of Long-Lasting Humoral and Cellular Immunity against SARS-CoV-2 Even in Elderly COVID-19 Convalescents Showing a Mild to Moderate Disease Progression

We here evaluate the humoral and cellular immune response against SARS-CoV-2 in 41 COVID-19 convalescents. As previous studies mostly included younger individuals, one advantage of our study is the comparatively high mean age of the convalescents included in the cohort considered (54 ± 8.4 years). While anti-SARS-CoV-2 antibodies were still detectable in 95% of convalescents up to 8 months post infection, an antibody-decay over time was generally observed in most donors. Using a multiplex assay, our data additionally reveal that most convalescents exhibit a broad humoral immunity against different viral epitopes. We demonstrate by flow cytometry that convalescent donors show a significantly elevated number of natural killer cells when compared to healthy controls, while no differences were found concerning other leucocyte subpopulations. We detected a specific long-lasting cellular immune response in convalescents by stimulating immune cells with SARS-CoV-2-specific peptides, covering domains of the viral spike, membrane and nucleocapsid protein, and measuring interferon-γ (IFN-γ) release thereafter. We modified a commercially available ELISA assay for IFN-γ determination in whole-blood specimens of COVID-19 convalescents. One advantage of this assay is that it does not require special equipment and can, thus, be performed in any standard laboratory. In conclusion, our study adds knowledge regarding the persistence of immunity of convalescents suffering from mild to moderate COVID-19. Moreover, our study provides a set of simple methods to characterize and confirm experienced COVID-19.

Seven-month kinetics of SARS-CoV-2 antibodies and role of pre-existing antibodies to human coronaviruses

Unraveling the long-term kinetics of antibodies to SARS-CoV-2 and the individual characteristics influencing it, including the impact of pre-existing antibodies to human coronaviruses causing common cold (HCoVs), is essential to understand protective immunity to COVID-19 and devise effective surveillance strategies. IgM, IgA and IgG levels against six SARS-CoV-2 antigens and the nucleocapsid antigen of the four HCoV (229E, NL63, OC43 and HKU1) were quantified by Luminex, and antibody neutralization capacity was assessed by flow cytometry, in a cohort of health care workers followed up to 7 months (N = 578). Seroprevalence increases over time from 13.5% (month 0) and 15.6% (month 1) to 16.4% (month 6). Levels of antibodies, including those with neutralizing capacity, are stable over time, except IgG to nucleocapsid antigen and IgM levels that wane. After the peak response, anti-spike antibody levels increase from ~150 days post-symptom onset in all individuals (73% for IgG), in the absence of any evidence of re-exposure. IgG and IgA to HCoV are significantly higher in asymptomatic than symptomatic seropositive individuals. Thus, pre-existing cross-reactive HCoVs antibodies could have a protective effect against SARS-CoV-2 infection and COVID-19 disease.

Successful treatment of COVID-19 infection with convalescent plasma in B-cell-depleted patients may promote cellular immunity

Treatment with convalescent plasma has been shown to be safe in coronavirus disease in 2019 (COVID‐19) infection, although efficacy reported in immunocompetent patients varies. Nevertheless, neutralizing antibodies are a key requisite in the fight against viral infections. Patients depleted of antibody‐producing B cells, such as those treated with rituximab (anti‐CD20) for hematological malignancies, lack a fundamental part of their adaptive immunity. Treatment with convalescent plasma appears to be of general benefit in this particularly vulnerable cohort. We analyzed clinical course and inflammation markers of three B‐cell‐depleted patients suffering from COVID‐19 who were treated with convalescent plasma. In addition, we measured serum antibody levels as well as peripheral blood CD38/HLA‐DR‐positive T‐cells ex vivo and CD137‐positive T‐cells after in vitro stimulation with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2)‐derived peptides in these patients. We observed that therapy with convalescent plasma was effective in all three patients and analysis of CD137‐positive T‐cells after stimulation with SARS‐CoV‐2 peptides showed an increase in peptide‐specific T‐cells after application of convalescent plasma.

In conclusion, we here demonstrate efficacy of convalescent plasma therapy in three B‐cell‐depleted patients and present data that suggest that while application of convalescent plasma elevates systemic antibody levels only transiently, it may also boost specific T‐cell responses.

SARS-CoV-2-specific serological and functional T cell immune responses during acute and early COVID-19 convalescence in solid organ transplant patients

The description of protective humoral and T cell immune responses specific against SARS-CoV-2 has been reported among immunocompetent (IC) individuals developing COVID-19 infection. However, its characterization and determinants of poorer outcomes among the at-risk solid organ transplant (SOT) patient population have not been thoroughly investigated. Cytokine-producing T cell responses, such as IFN-γ, IL-2, IFN-γ/IL-2, IL-6, IL-21, and IL-5, against main immunogenic SARS-CoV-2 antigens and IgM/IgG serological immunity were tracked in SOT (n = 28) during acute infection and at two consecutive time points over the following 40 days of convalescence and were compared to matched IC (n = 16) patients admitted with similar moderate/severe COVID-19. We describe the development of a robust serological and functional T cell immune responses against SARS-CoV-2 among SOT patients, similar to IC patients during early convalescence. However, at the infection onset, SOT displayed lower IgG seroconversion rates (77% vs. 100%; p = .044), despite no differences on IgG titers, and a trend toward decreased SARS-CoV-2-reactive T cell frequencies, especially against the membrane protein (7 [0-34] vs. 113 [15-245], p = .011, 2 [0-9] vs. 45 [5-74], p = .009, and 0 [0-2] vs. 13 [1-24], p = .020, IFN-γ, IL-2, and IFN-γ/IL-2 spots, respectively). In summary, our data suggest that despite a certain initial delay, SOT population achieve comparable functional immune responses than the general population after moderate/severe COVID-19.

Serial SARS-CoV-2 Receptor-Binding Domain Antibody Responses in Patients Receiving Dialysis

BACKGROUND

Assessing the evolution of SARS-CoV-2 immune response among patients receiving dialysis can define its durability in a highly clinically relevant context because patients receiving dialysis share the characteristics of persons most susceptible to SARS-CoV-2 infection.

OBJECTIVE

To evaluate the persistence of SARS-CoV-2 receptor-binding domain (RBD) IgG in seroprevalent patients receiving dialysis.

DESIGN

Prospective.

SETTING

Nationwide sample from dialysis facilities.

PATIENTS

2215 patients receiving dialysis who had evidence of SARS-CoV-2 infection as of July 2020.

MEASUREMENTS

Remainder plasma from routine monthly laboratories was used to measure semiquantitative RBD IgG index value over 6 months.

RESULTS

A total of 2063 (93%) seroprevalent patients reached an assay detectable response (IgG index value ≥1). Most (n = 1323, 60%) had responses in July with index values classified as high (IgG ≥10); 1003 (76%) remained within this stratum. Adjusted median index values declined slowly but continuously (July vs. December values were 21 vs. 13; P < 0.001). The trajectory of the response did not vary by age group, sex, race/ethnicity, or diabetes status. Patients without an assay detectable response (n = 137) were more likely to be White and in the younger (18 to 44 years) or older (≥80 years) age groups and less likely to have diabetes and hypoalbuminemia.

LIMITATION

Lack of data on symptoms or reverse transcriptase polymerase chain reaction diagnosis, cohort of persons who survived infection, and use of a semiquantitative assay.

CONCLUSION

Despite impaired immunity, most seropositive patients receiving dialysis maintained RBD antibody levels over 6 months. A slow and continual decline in median antibody levels over time was seen, but no indication that subgroups with impaired immunity had a shorter-lived humoral response was found.

PRIMARY FUNDING SOURCE

Ascend Clinical Laboratories.

Key Considerations for the Development of Safe and Effective SARS-CoV-2 Subunit Vaccine: A Peptide-Based Vaccine Alternative

COVID-19 is disastrous to global health and the economy. SARS-CoV-2 infection exhibits similar clinical symptoms and immunopathological sequelae to SARS-CoV infection. Therefore, much of the developmental progress on SARS-CoV vaccines can be utilized for the development of SARS-CoV-2 vaccines. Careful antigen selection during development is always of utmost importance for the production of effective vaccines that do not compromise recipient safety. This holds especially true for SARS-CoV vaccines, as several immunopathological disorders are associated with the activity of structural and nonstructural proteins encoded in the virus's genetic material. Whole viral protein and RNA-encoding full-length proteins contain both protective and "dangerous" sequences, unless pathological fragments are deleted. In light of recent advances, peptide vaccines may present a very safe and effective alternative. Peptide vaccines can avoid immunopathological pro-inflammatory sequences, focus immune responses on neutralizing immunogenic epitopes, avoid off-target antigen loss, combine antigens with different protective roles or mechanisms, even from different viral proteins, and avoid mutant escape by employing highly conserved cryptic epitopes. In this review, an attempt is made to exploit the similarities between SARS-CoV and SARS-CoV-2 in vaccine antigen screening, with particular attention to the pathological and immunogenic properties of SARS proteins.

SARS-CoV-2-directed antibodies persist for more than six months in a cohort with mild to moderate COVID-19

OBJECTIVE

To follow serological immune responses of front-line healthcare workers after PCR-confirmed COVID-19 for a mean of 30 weeks, describe the time-course of SARS-CoV-2 spike protein-specific IgG, IgA and IgM levels and to identify associations of the immune response with symptoms, demographic parameters and severity of disease.

METHODS

Anti-SARS-CoV-2 S protein-specific IgG, IgA and IgM antibodies were measured at three time points during the 30-week follow-up. COVID-19-specific symptoms were assessed with standardized questionnaires.

RESULTS

95% of the participants mounted an IgG response with only modest decline after week 12. IgG-type antibodies were still detectable in almost 90% of the subjects at 30 weeks. IgA and IgM responses were less robust and antibody titers decreased more rapidly. At 30 weeks, only 25% still had detectable IgA-type and none had IgM-type antibodies. Higher age and higher disease severity were independently associated with higher IgG antibody levels, albeit with wide variations.

CONCLUSION

Serological immune responses after COVID-19 show considerable inter-individual variability, but show an association with increasing age and higher severity of disease. IgG-type anti-SARS-CoV-2 antibodies remain positive in 90% of the individuals 30 weeks after onset of symptoms.

Poor humoral and T-cell response to two-dose SARS-CoV-2 messenger RNA vaccine BNT162b2 in cardiothoracic transplant recipients

AIMS

Immunocompromised patients have been excluded from studies of SARS-CoV-2 messenger RNA vaccines. The immune response to vaccines against other infectious agents has been shown to be blunted in such patients. We aimed to analyse the humoral and cellular response to prime-boost vaccination with the BNT162b2 vaccine (Pfizer-BioNTech) in cardiothoracic transplant recipients.

METHODS AND RESULTS

A total of 50 transplant patients [1-3 years post heart (42), lung (7), or heart-lung (1) transplant, mean age 55 ± 10 years] and a control group of 50 healthy staff members were included. Blood samples were analysed 21 days after the prime and the boosting dose, respectively, to quantify anti-SARS-CoV-2 spike protein (S) immunoglobulin titres (tested by Abbott, Euroimmun and RocheElecsys Immunoassays, each) and the functional inhibitory capacity of neutralizing antibodies (Genscript). To test for a specific T-cell response, heparinized whole blood was stimulated with SARS-CoV-2 specific peptides, covering domains of the viral spike, nucleocapsid and membrane protein, and the interferon-γ release was measured (QuantiFERON Monitor ELISA, Qiagen). The vast majority of transplant patients (90%) showed neither a detectable humoral nor a T-cell response three weeks after the completed two-dose BNT162b2 vaccination; these results are in sharp contrast to the robust immunogenicity seen in the control group: 98% exhibited seroconversion after the prime dose already, with a further significant increase of IgG titres after the booster dose (average > tenfold increase), a more than 90% inhibition capability of neutralizing antibodies as well as evidence of a T-cell responsiveness.

CONCLUSIONS

The findings of poor immune responses to a two-dose BNT162b2 vaccination in cardiothoracic transplant patients have a significant impact for organ transplant recipients specifically and possibly for immunocompromised patients in general. It urges for a review of future vaccine strategies in these patients.

Potential SARS-CoV-2 vaccines: Concept, progress, and challenges

Since September 2020, the world has had more than 28 million cases of coronavirus disease 2019 (COVID-19). Many countries are facing a second wave of the COVID-19 outbreak. A pressing need is evident for the development of a potent vaccine to control the SARS-CoV-2. Institutions and companies in many countries have announced their vaccine research programs and progress against the COVID-19. While most vaccines go through the designation and preparation stages, some of them are under evaluation for efficacy among animal models and clinical trials, and three approved vaccine candidates have been introduced for limited exploitation in Russia and China. An effective vaccine must induce a protective response of both cell-mediated and humoral immunity and should meet the safety and efficacy criteria. Although the emergence of new technologies has accelerated the development of vaccines, there are several challenges on the way, such as limited knowledge about the pathophysiology of the virus, inducing humoral or cellular immunity, immune enhancement with animal coronavirus vaccines, and lack of an appropriate animal model. In this review, we firstly discuss the immune responses against SARS-CoV-2 disease, subsequently, give an overview of several vaccine platforms for SARS-CoV-2 under clinical trials and challenges in vaccine development against this virus.

Longitudinal observation of antibody responses for 14 months after SARS-CoV-2 infection

Better understanding of antibody responses against SARS-CoV-2 after natural infection might provide valuable insights into the future implementation of vaccination policies. Longitudinal analysis of IgG antibody titers was carried out in 32 recovered COVID-19 patients based in the Umbria region of Italy for 14 months after Mild and Moderately-Severe infection.Two FDA-approved immunoassays against SARS-CoV-2 Nucleocapsid protein (NCP) and anti-spike-receptor binding domain (S-RBD) were used for sequential serological tests at different time points. The demographics,clinical history and symptom profile associated with the magnitude and longevity of antibody responses were also analyzed. Anti-S-RBD IgG persisted in 96.8% (31 of 32) subjects at 14 months. Patients reporting loss of smell and taste during the clinical course of the disease developed significantly higher antibody titers. Anti-NCP IgG seronegative patients(n=7) at 10 months, tested positive for anti-S-RBD IgG at 12,13 and 14 months emphasizing on a higher false-negative rate for NCP protein-based antibody assays. This study also highlights the importance of adopting specific immunoassays for routine estimation of antibody titers and the decreased rate of re-infections in recovered patients.

Know your enemy or find your friend?-Induction of IgA at mucosal surfaces

Most antibodies produced in the body are of the IgA class. The dominant cell population producing them are plasma cells within the lamina propria of the gastrointestinal tract, but many IgA-producing cells are also found in the airways, within mammary tissues, the urogenital tract and inside the bone marrow. Most IgA antibodies are transported into the lumen by epithelial cells as part of the mucosal secretions, but they are also present in serum and other body fluids. A large part of the commensal microbiota in the gut is covered with IgA antibodies, and it has been demonstrated that this plays a role in maintaining a healthy balance between the host and the bacteria. However, IgA antibodies also play important roles in neutralizing pathogens in the gastrointestinal tract and the upper airways. The distinction between the two roles of IgA - protective and balance-maintaining - not only has implications on function but also on how the production is regulated. Here, we discuss these issues with a special focus on gut and airways.

SARS-CoV-2 serology after COVID-19 in multiple sclerosis: An international cohort study

BACKGROUND

The MuSC-19 project is an Italian cohort study open to international partners that collects data on multiple sclerosis (MS) patients with COVID-19. During the second wave of the pandemic, serological tests became routinely available.

OBJECTIVE

To evaluate the seroprevalence of anti-SARS-CoV-2 antibodies according to the use of disease-modifying therapy (DMT) in a subset of patients included in the MuSC-19 data set who had undergone a serological test.

METHODS

We evaluated the association between positive serological test results and time elapsed since infection onset, age, sex, Expanded Disability Status Scale score, comorbidities and DMT exposure using a multivariable logistic model.

RESULTS

Data were collected from 423 patients (345 from Italy, 61 from Turkey and 17 from Brazil) with a serological test performed during follow-up. Overall, 325 out of 423 tested patients (76.8%) had a positive serological test. At multivariate analysis, therapy with anti-CD20 was significantly associated with a reduced probability of developing antibodies after COVID-19 (odds ratio (OR) = 0.20, p = 0.002).

CONCLUSION

Patients with MS maintain the capacity to develop humoral immune response against SARS-COV-2, although to a lesser extent when treated with anti-CD20 drugs. Overall, our results are reassuring with respect to the possibility to achieve sufficient immunization with vaccination.

Primary, Recall, and Decay Kinetics of SARS-CoV-2 Vaccine Antibody Responses

Studies of two SARS-CoV-2 mRNA vaccines suggested that they yield ∼95% protection from symptomatic infection at least short-term, but important clinical questions remain. It is unclear how vaccine-induced antibody levels quantitatively compare to the wide spectrum induced by natural SARS-CoV-2 infection. Vaccine response kinetics and magnitudes in persons with prior COVID-19 compared to virus-naı̈ve persons are not well-defined. The relative stability of vaccine-induced versus infection-induced antibody levels is unclear. We addressed these issues with longitudinal assessments of vaccinees with and without prior SARS-CoV-2 infection using quantitative enzyme-linked immunosorbent assay (ELISA) of anti-RBD antibodies. SARS-CoV-2-naı̈ve individuals achieved levels similar to mild natural infection after the first vaccination; a second dose generated levels approaching severe natural infection. In persons with prior COVID-19, one dose boosted levels to the high end of severe natural infection even in those who never had robust responses from infection, increasing no further after the second dose. Antiviral neutralizing assessments using a spike-pseudovirus assay revealed that virus-naı̈ve vaccinees did not develop physiologic neutralizing potency until the second dose, while previously infected persons exhibited maximal neutralization after one dose. Finally, antibodies from vaccination waned similarly to natural infection, resulting in an average of ∼90% loss within 90 days. In summary, our findings suggest that two doses are important for quantity and quality of humoral immunity in SARS-CoV-2-naı̈ve persons, while a single dose has maximal effects in those with past infection. Antibodies from vaccination wane with kinetics very similar to that seen after mild natural infection; booster vaccinations will likely be required.

Evaluation of S-RBD and high specificity ACE-2-binding antibodies on SARS-CoV-2 patients after six months from infection

The antibody response to SARS-CoV-2 has not yet fully defined, but the availability of sensitive and specific serological assays is crucial to observe the presence of specific antibodies against the human receptor binding domain (S-RBD) and high specificity ACE-2-binding antibodies or neutralizing antibodies (NT) in response to vaccines. Indeed, these peculiar antibodies should prevent viral interaction between RBD and Angiotensin-Converting Enzyme 2 (ACE2) receptor, located on surface of host cells. In this study, 72 samples from 37 hospitalized COVID-19 patients and 35 not-hospitalized patients were analyzed longitudinally. The detection of S-RBD and NT antibodies was carried out using CLIA tests.

Hospitalized patients showed elevated serum levels of S-RBD (97.22%) and NT (77.78%) antibodies, differently, not-hospitalized, who were paucisymptomatic or asymptomatic patients, showed lower serum levels of S-RBD (65.71%) and NT (38.14%) antibodies.

The results suggest that the NT serum level is strongly related to disease severity (p < 0.001) and to the serum level of S-RBD antibodies (p < 0.0001).

Decline in neutralising antibody responses, but sustained T-cell immunity, in COVID-19 patients at 7 months post-infection

Objectives

This study aimed to explore the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific humoral responses and T-cell responses in patients who have recovered from coronavirus disease 2019 (COVID-19) to understand the natural protective immune responses and to facilitate the development of vaccines.

Methods

We conducted a combined assessment of the changes in neutralising antibody levels and SARS-CoV-2-specific T-cell responses over time in 27 patients up to 7 months after infection.

Results

The neutralising antibody remained detectable in 96.3% of the patients at their second visit at about 7 months post-onset of symptoms. However, their humoral responses, including titres of the spike receptor-binding domain IgG and neutralising antibody, decreased significantly compared with those at first clinic visit. By contrast, the proportions of spike-specific CD4⁺ T cells, but not CD8⁺ T cells, in COVID-19 patients after recovery were persistently higher than those in healthy controls. No significant change was observed in the proportion of spike-specific CD4⁺ T cells in patients who had recovered from COVID-19 within 7 months.

Conclusion

The SARS-CoV-2-specific T-cell immune responses persisted, while the neutralising antibodies decayed. Further studies are needed to extend the longevity of neutralising antibodies and to evaluate whether these T cells are sufficient to protect patients from reinfection.

Ultrasensitive, high-throughput, and rapid simultaneous detection of SARS-CoV-2 antigens and IgG/IgM antibodies within 10 min through an immunoassay biochip

COVID-19 is now a severe threat to global health. Facing this pandemic, we developed a space-encoding microfluidic biochip for high-throughput, rapid, sensitive, simultaneous quantitative detection of SARS-CoV-2 antigen proteins and IgG/IgM antibodies in serum. The proposed immunoassay biochip integrates the advantages of graphene oxide quantum dots (GOQDs) and microfluidic chip and is capable of conducting multiple SARS-CoV-2 antigens or IgG/IgM antibodies of 60 serum samples simultaneously with only 2 μL sample volume of each patient. Fluorescence intensity of antigens and IgG antibody detection at emission wavelength of ~680 nm was used to quantify the target concentration at excitation wavelength of 632 nm, and emission wavelength of ~519 nm was used during the detection of IgM antibodies at excitation wavelength of 488 nm. The method developed has a large linear quantification detection regime of 5 orders of magnitude, an ultralow detection limit of ~0.3 pg/mL under optimized conditions, and less than 10-min qualitative detection time. The proposed biosensing platform will not only greatly facilitate the rapid diagnosis of COVID-19 patients, but also provide a valuable screening approach for infected patients, medical therapy, and vaccine recipients.

Coronavirus Occurrence in the Household Influenza Vaccine Evaluation (HIVE) Cohort of Michigan Households: Reinfection Frequency and Serologic Responses to Seasonal and Severe Acute Respiratory Syndrome Coronaviruses

BACKGROUND

We investigated frequency of reinfection with seasonal human coronaviruses (HCoVs) and serum antibody response following infection over 8 years in the Household Influenza Vaccine Evaluation (HIVE) cohort.

METHODS

Households were followed annually for identification of acute respiratory illness with reverse-transcription polymerase chain reaction-confirmed HCoV infection. Serum collected before and at 2 time points postinfection were tested using a multiplex binding assay to quantify antibody to seasonal, severe acute respiratory syndrome coronavirus (SARS-CoV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike proteins and SARS-CoV-2 spike subdomains and N protein.

RESULTS

Of 3418 participants, 40% were followed for ≥3 years. A total of 1004 HCoV infections were documented; 303 (30%) were reinfections of any HCoV type. The number of HCoV infections ranged from 1 to 13 per individual. The mean time to reinfection with the same type was estimated at 983 days for 229E, 578 days for HKU1, 615 days for OC43, and 711 days for NL63. Binding antibody levels to seasonal HCoVs were high, with little increase postinfection, and were maintained over time. Homologous, preinfection antibody levels did not significantly correlate with odds of infection, and there was little cross-response to SARS-CoV-2 proteins.

CONCLUSIONS

Reinfection with seasonal HCoVs is frequent. Binding anti-spike protein antibodies do not correlate with protection from seasonal HCoV infection.