Kinetics of specific anti-SARS-CoV-2 IgM, IgA, and IgG responses during the first 12 months after SARS-CoV-2 infection: A prospective longitudinal study

Dynamics of SARS-CoV-2 antibodies after natural infection: insights from a study on Pasteur Institute of Tunis employees

This study aimed to assess the kinetics of antibodies against the SARS-CoV-2, following natural infection in a cohort of employees of the Institut Pasteur de Tunis (IPT) and to assess the risk of reinfection over a 12-months follow-up period. A prospective study was conducted among an open cohort of IPT employees with confirmed SARS-CoV-2 infection that were recruited between September 2020 and March 2021. Sera samples were taken at 1, 3, 6, 9 and 12 months after confirmation of COVID-19 infection and tested for SARS-CoV-2-specific immunoglobulin G (IgG) antibodies to the spike (S-RBD) protein (IgG anti-S-RBD) and for neutralizing antibodies. Participants who had an initial decline of IgG anti-S-RBD and neutralizing antibodies followed by a subsequent rise in antibody titers as well as those who tested positive for SARS-CoV-2 by RT-PCR after at least 60 days of follow up were considered as reinfected. In total, 137 individuals were included with a mean age of 44.7 ± 12.3 years and a sex-ratio (Male/Female) of 0.33. Nearly all participants (92.7%) were symptomatic, and 2.2% required hospitalization. Among the 70 participants with three or more prospective blood samples, 32.8% were reinfected among whom 11 (47.8%) reported COVID-19 like symptoms. Up to 12 months of follow up, 100% and 42.9% of participants had detectable IgG anti-S-RBD and neutralizing antibodies, respectively. This study showed that humoral immune response following COVID-19 infection may persist up to 12 months after infection despite the potential risk for reinfection that is mainly explained by the emergence of new variants.

Unravelling humoral immunity in SARS-CoV-2: Insights from infection and vaccination

Following infection and vaccination against SARS-CoV-2, humoral components of the adaptive immune system play a key role in protecting the host. Specifically, B cells generate high-affinity antibodies against various antigens of the virus. In this review, we discuss the mechanisms of immunity initiation through both natural infection and vaccination, shedding light on the activation of B cell subsets in response to SARS-CoV-2 infection and vaccination. The innate immune system serves as the initial line of primary and nonspecific defence against viruses. However, within several days following infection or a vaccine dose, a virus-specific immune response is initiated, primarily by B cells that produce antibodies. These antibodies contribute to the resolution of the disease. Subsequently, these B cells transition into memory B cells, which play a crucial role in providing long-term immunity against the virus. CD4+ T helper cells initiate a cascade, leading to B cell somatic hypermutation, germinal center memory B cells, and the production of neutralizing antibodies. B-cell dysfunction can worsen disease severity and reduce vaccine efficacy. Notably, individuals with B cell immunodeficiency show lower IL-6 production. Furthermore, this review delves into several aspects of immune responses, such as hybrid immunity, which has shown promise in boosting broad-spectrum protection. Cross-reactive immunity is under scrutiny as well, as pre-existing antibodies can offer protection against the disease. We also decipher breakthrough infection mechanisms, especially with the novel variants of the virus. Finally, we discuss some potential therapeutic solutions regarding B cells including convalescent plasma therapy, B-1 cells, B regulatory cell (Breg) modulation, and the use of neutralizing monoclonal antibodies in combating the infection. Ongoing research is crucial to grasp population immunity trends and assess the potential need for booster doses in maintaining effective immune responses against potential viral threats.

Reduced control of SARS-CoV-2 infection associates with lower mucosal antibody responses in pregnancy

Pregnant patients are at greater risk of hospitalization with severe COVID-19 than non-pregnant people. This was a retrospective observational cohort study of remnant clinical specimens from patients who visited acute care hospitals within the Johns Hopkins Health System in the Baltimore, MD-Washington DC, area between October 2020 and May 2022. Participants included confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected pregnant people and matched non-pregnant people (the matching criteria included age, race/ethnicity, area deprivation index, insurance status, and vaccination status to ensure matched demographics). The primary dependent measures were clinical COVID-19 outcomes, infectious virus recovery, viral RNA levels, and mucosal anti-spike (S) IgG titers from upper respiratory tract samples. A total of 452 individuals (117 pregnant and 335 non-pregnant) were included in the study, with both vaccinated and unvaccinated individuals represented. Pregnant patients were at increased risk of hospitalization (odds ratio [OR] = 4.2; confidence interval [CI] = 2.0-8.6), intensive care unit admittance (OR = 4.5; CI = 1.2-14.2), and being placed on supplemental oxygen therapy (OR = 3.1; CI = 1.3-6.9). Individuals infected during their third trimester had higher mucosal anti-S IgG titers and lower viral RNA levels (P < 0.05) than those infected during their first or second trimesters. Pregnant individuals experiencing breakthrough infections due to the Omicron variant had reduced anti-S IgG compared to non-pregnant patients (P < 0.05). The observed increased severity of COVID-19 and reduced mucosal antibody responses particularly among pregnant participants infected with the Omicron variant suggest that maintaining high levels of SARS-CoV-2 immunity through booster vaccines may be important for the protection of this at-risk population.IMPORTANCEIn this retrospective observational cohort study, we analyzed remnant clinical samples from non-pregnant and pregnant individuals with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections who visited the Johns Hopkins Hospital System between October 2020 and May 2022. Disease severity, including intensive care unit admission, was greater among pregnant than non-pregnant patients. Vaccination reduced recovery of infectious virus and viral RNA levels in non-pregnant patients, but not in pregnant patients. In pregnant patients, increased nasopharyngeal viral RNA levels and recovery of infectious virus were associated with reduced mucosal IgG antibody responses, especially among women in their first trimester of pregnancy or experiencing breakthrough infections from Omicron variants. Taken together, this study provides insights into how pregnant patients are at greater risk of severe COVID-19. The novelty of this study is that it focuses on the relationship between the mucosal antibody response and its association with virus load and disease outcomes in pregnant people, whereas previous studies have focused on serological immunity. Vaccination status, gestational age, and SARS-CoV-2 omicron variant impact mucosal antibody responses and recovery of infectious virus from pregnant patients.

SARS-CoV-2 infection, inflammation and birth outcomes in a prospective NYC pregnancy cohort

Associations between antenatal SARS-CoV-2 infection and pregnancy outcomes have been conflicting and the role of the immune system is currently unclear. This prospective cohort study investigated the interaction of antenatal SARS-CoV-2 infection, changes in cytokine and HS-CRP levels, birthweight and gestational age at birth. 2352 pregnant participants from New York City (2020-2022) were included. Plasma levels of interleukin (IL)-1β, IL-6, IL-17A and high-sensitivity C-reactive protein (HS-CRP) were quantified in blood specimens obtained across pregnancy. Quantile and linear regression models were conducted to 1) assess the impact of antenatal SARS-CoV-2 infection, overall and by timing of detection of SARS-CoV-2 positivity (< 20 weeks versus ≥ 20 weeks), on birthweight and gestational age at delivery; 2) examine the relationship between SARS-CoV-2 infection and maternal immune changes during pregnancy. All models were adjusted for maternal demographic and obstetric factors and pandemic timing. Birthweight models were additionally adjusted for gestational age at delivery and fetal sex. Immune marker models were also adjusted for gestational age at specimen collection and multiplex assay batch. 371 (15.8%) participants were infected with SARS-CoV-2 during pregnancy, of which 98 (26.4%) were infected at < 20 weeks gestation. Neither SARS-CoV-2 infection in general nor in early or late pregnancy was associated with lower birthweight nor earlier gestational age at delivery. Further, we did not observe cytokine or HS-CRP changes in response to SARS-CoV-2 infection and thus found no evidence to support a potential association between immune dysregulation and the diversity in pregnancy outcomes following infection.

The subdued post-boost spike-directed secondary IgG antibody response in Ugandan recipients of the Pfizer-BioNTech BNT162b2 vaccine has implications for local vaccination policies

Introduction

This study aimed to delineate longitudinal antibody responses to the Pfizer-BioNTech BNT162b2 COVID-19 vaccine within the Ugandan subset of the Sub-Saharan African (SSA) demographic, filling a significant gap in global datasets.

Methods

We enrolled 48 participants and collected 320 specimens over 12 months after the primary vaccination dose. A validated enzyme-linked immunosorbent assay (ELISA) was used to quantify SARS-CoV-2-specific IgG, IgM, and IgA antibody concentrations (ng/ml) and optical densities (ODs). Statistical analyses included box plots, diverging bar graphs, and the Wilcoxon test with Bonferroni correction.

Results

We noted a robust S-IgG response within 14 days of the primary vaccine dose, which was consistent with global data. There was no significant surge in S-IgG levels after the booster dose, contrasting trends in other global populations. The S-IgM response was transient and predominantly below established thresholds for this population, which reflects its typical early emergence and rapid decline. S-IgA levels rose after the initial dose then decreased after six months, aligning with the temporal patterns of mucosal immunity. Eleven breakthrough infections were noted, and all were asymptomatic, regardless of the participants' initial S-IgG serostatus, which suggests a protective effect from vaccination.

Discussion

The Pfizer-BioNTech BNT162b2 COVID-19 vaccine elicited strong S-IgG responses in the SSA demographic. The antibody dynamics distinctly differed from global data highlighting the significance of region-specific research and the necessity for customised vaccination strategies.

Mapping IgA Epitope and Cross-Reactivity between Severe Acute Respiratory Syndrome-Associated Coronavirus 2 and DENV

BACKGROUND

The newly introduced COVID-19 vaccines have reduced disease severity and hospitalizations. However, they do not significantly prevent infection or transmission. In the same context, measuring IgM and IgG antibody levels is important, but it does not provide information about the status of the mucosal immune response. This article describes a comprehensive mapping of IgA epitopes of the S protein, its cross-reactivity, and the development of an ELISA-peptide assay.

METHODS

IgA epitope mapping was conducted using SPOT synthesis and sera from RT-qPCR COVID-19-positive patients. Specific and cross-reacting epitopes were identified, and an evolutionary analysis from the early Wuhan strain to the Omicron variant was performed using bioinformatics tools and a microarray of peptides. The selected epitopes were chemically synthesized and evaluated using ELISA-IgA.

RESULTS

A total of 40 IgA epitopes were identified with 23 in S1 and 17 in the S2 subunit. Among these, at least 23 epitopes showed cross-reactivity with DENV and other organisms and 24 showed cross-reactivity with other associated coronaviruses. Three MAP4 polypeptides were validated by ELISA, demonstrating a sensitivity of 90-99.96% and a specificity of 100%. Among the six IgA-RBD epitopes, only the SC/18 epitope of the Omicron variants (BA.2 and BA.2.12.1) presented a single IgA epitope.

CONCLUSIONS

This research unveiled the IgA epitome of the S protein and identified many epitopes that exhibit cross-reactivity with DENV and other coronaviruses. The S protein of variants from Wuhan to Omicron retains many conserved IgA epitopes except for one epitope (#SCov/18). The cross-reactivity with DENV suggests limitations in using the whole S protein or the S1/S2/RBD segment for IgA serological diagnostic tests for COVID-19. The expression of these identified specific epitopes as diagnostic biomarkers could facilitate monitoring mucosal immunity to COVID-19, potentially leading to more accurate diagnoses and alternative mucosal vaccines.

Longitudinal anti-SARS-CoV-2 antibody immune response in acute and convalescent patients

Despite global efforts to assess the early response and persistence of SARS-CoV-2 antibodies in patients infected with or recovered from COVID-19, our understanding of the factors affecting its dynamics remains limited. This work aimed to evaluate the early and convalescent immunity of outpatients infected with SARS-CoV-2 and to determine the factors that affect the dynamics and persistence of the IgM and IgG antibody response. Seropositivity of volunteers from Mexico City and the State of Mexico, Mexico, was evaluated by ELISA using the recombinant receptor-binding domain (RBD) of the SARS-CoV-2 Spike protein for 90 days, at different time points (1, 15, 45, 60, and 90 days) after molecular diagnosis (RT-qPCR). Gender, age range, body mass index (BMI), comorbidities, and clinical spectrum of disease were analyzed to determine associations with the dynamics of anti-SARS-CoV-2 antibodies. On 90 days post-infection, individuals with moderate and asymptomatic disease presented the lowest levels of IgM, while for IgG, at the same time, the highest levels occurred with mild and moderate disease. The IgM and IgG levels were related to the clinical spectrum of disease, BMI, and the presence/absence of comorbidities through regression trees. The results suggest that the dynamics of anti-SARS-CoV-2 IgM and IgG antibodies in outpatients could be influenced by the clinical spectrum of the disease. In addition, the persistence of antibodies against SARS-CoV-2 could be related to the clinical spectrum of the disease, BMI, and the presence/absence of comorbidities.