Longitudinal Dynamics of the Neutralizing Antibody Response to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection

Hybrid response to SARS-CoV-2 and Neisseria meningitidis C after an OMV-adjuvanted immunization in mice and their offspring

COVID-19, caused by SARS-CoV-2, and meningococcal disease, caused by Neisseria meningitidis, are relevant infectious diseases, preventable through vaccination. Outer membrane vesicles (OMVs), released from Gram-negative bacteria, such as N. meningitidis, present adjuvant characteristics and may confer protection against meningococcal disease. Here, we evaluated in mice the humoral and cellular immune response to different doses of receptor binding domain (RBD) of SARS-CoV-2 adjuvanted by N. meningitidis C:2a:P1.5 OMVs and aluminum hydroxide, as a combined preparation for these pathogens. The immunization induced IgG antibodies of high avidity for RBD and OMVs, besides IgG that recognized the Omicron BA.2 variant of SARS-CoV-2 with intermediary avidity. Cellular immunity showed IFN-γ and IL-4 secretion in response to RBD and OMV stimuli, demonstrating immunologic memory and a mixed Th1/Th2 response. Offspring presented transferred IgG of similar levels and avidity as their mothers. Humoral immunity did not point to the superiority of any RBD dose, but the group immunized with a lower antigenic dose (0.5 μg) had the better cellular response. Overall, OMVs enhanced RBD immunogenicity and conferred an immune response directed to N. meningitidis too.

SARS-CoV-2 Antibody Kinetics in Unvaccinated Hospitalized Children With COVID-19

BACKGROUND

Antibody levels decline a few months post-acute COVID-19, but humoral memory persists in adults. Age and disease severity may affect antibody responses. This study aims to evaluate the presence and durability of antibody responses in children with COVID-19.

METHODS

A prospective, single-center study, involving unvaccinated children 0-16 years of age who were hospitalized with COVID-19 between October 2020 and December 2021, was conducted. Serological testing for anti-Spike severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) IgG and neutralizing antibodies was performed at diagnosis and at 1-, 3-, 6- and 12-months post-infection.

RESULTS

A total of 65 immunocompetent children were enrolled [mean age (±SD): 6.7 (±6.4) years; males: 56.9%]. At 3 months, 40/44 (91%) children were seropositive; seropositivity persisted in 22/26 (85%) children at 6 months and in 10/12 (83%) children at 12 months. There was no evidence that age was modifying the prediction of variance of SARS-CoV-2 IgG levels. In contrast, SARS-CoV-2 IgG levels varied with time and disease severity. The association with time was non-linear, so that with increasing time there was a significant reduction in SARS-CoV-2 IgG levels [coef, 0.044 (95% confidence interval {CI}: 0.061-0.028), P < 0.001]. For each increment of time, the higher disease severity group was associated with 0.9 lower SARS-CoV-2 IgG levels. Everyone varied from the average effect of time with an SD of 0.01, suggesting that individuals may have different trajectories across time.

CONCLUSION

Disease severity, but not age, influences antibody titers among children hospitalized with COVID-19. SARS-CoV-2 infection induces durable seroconversion in these children with detectable IgG levels at 1 year after infection.

Boosting the immunogenicity of the CoronaVac SARS-CoV-2 inactivated vaccine with Huoxiang Suling Shuanghua Decoction: a randomized, double-blind, placebo-controlled study

Introduction

In light of the public health burden of the COVID-19 pandemic, boosting the safety and immunogenicity of COVID-19 vaccines is of great concern. Numerous Traditional Chinese medicine (TCM) preparations have shown to beneficially modulate immunity. Based on pilot experiments in mice that showed that supplementation with Huoxiang Suling Shuanghua Decoction (HSSD) significantly enhances serum anti-RBD IgG titers after inoculation with recombinant SARS-CoV-2 S-RBD protein, we conducted this randomized, double-blind, placebo-controlled clinical trial aimed to evaluate the potential immunogenicity boosting effect of oral HSSD after a third homologous immunization with Sinovac's CoronaVac SARS-CoV-2 (CVS) inactivated vaccine.

Methods

A total of 70 participants were randomly assigned (1:1 ratio) to receive a third dose of CVS vaccination and either oral placebo or oral HSSD for 7 days. Safety aspects were assessed by recording local and systemic adverse events, and by blood and urine biochemistry and liver and kidney function tests. Main outcomes evaluated included serum anti-RBD IgG titer, T lymphocyte subsets, serum IgG and IgM levels, complement components (C3 and C4), and serum cytokines (IL-6 and IFN-γ). In addition, metabolomics technology was used to analyze differential metabolite expression after supplementation with HSSD.

Results

Following a third CVS vaccination, significantly increased serum anti-RBD IgG titer, reduced serum IL-6 levels, increased serum IgG, IgM, and C3 and C4 levels, and improved cellular immunity, evidenced by reduce balance deviations in the distribution of lymphocyte subsets, was observed in the HSSD group compared with the placebo group. No serious adverse events were recorded in either group. Serum metabolomics results suggested that the mechanisms by which HSSD boosted the immunogenicity of the CVS vaccine are related to differential regulation of purine metabolism, vitamin B6 metabolism, folate biosynthesis, arginine and proline metabolism, and steroid hormone biosynthesis.

Conclusion

Oral HSSD boosts the immunogenicity of the CVS vaccine in young and adult individuals. This trial provides clinical reference for evaluation of TCM immunomodulators to improve the immune response to COVID-19 vaccines.

Immunization-induced antigen archiving enhances local memory CD8+ T cell responses following an unrelated viral infection

Antigens from viruses or immunizations can persist or are archived in lymph node stromal cells such as lymphatic endothelial cells (LEC) and fibroblastic reticular cells (FRC). Here, we find that, during the time frame of antigen archiving, LEC apoptosis caused by a second, but unrelated, innate immune stimulus such as vaccina viral infection or CpG DNA administration resulted in cross-presentation of archived antigens and boosted memory CD8 + T cells specific to the archived antigen. In contrast to "bystander" activation associated with unrelated infections, the memory CD8 + T cells specific to the archived antigen from the immunization were significantly higher than memory CD8 + T cells of a different antigen specificity. Finally, the boosted memory CD8 + T cells resulted in increased protection against Listeria monocytogenes expressing the antigen from the immunization, but only for the duration that the antigen was archived. These findings outline an important mechanism by which lymph node stromal cell archived antigens, in addition to bystander activation, can augment memory CD8 + T cell responses during repeated inflammatory insults.

A comprehensive review on immunogen and immune-response proteins of SARS-CoV-2 and their applications in prevention, diagnosis, and treatment of COVID-19

Exposure to severe acute respiratory syndrome-corona virus-2 (SARS-CoV-2) prompts humoral immune responses in the human body. As the auxiliary diagnosis of a current infection, the existence of viral proteins can be checked from specific antibodies (Abs) induced by immunogenic viral proteins. For people with a weakened immune system, Ab treatment can help neutralize viral antigens to resist and treat the disease. On the other hand, highly immunogenic viral proteins can serve as effective markers for detecting prior infections. Additionally, the identification of viral particles or the presence of antibodies may help establish an immune defense against the virus. These immunogenic proteins rather than SARS-CoV-2 can be given to uninfected people as a vaccination to improve their coping ability against COVID-19 through the generation of memory plasma cells. In this work, we review immunogenic and immune-response proteins derived from SARS-CoV-2 with regard to their classification, origin, and diverse applications (e.g., prevention (vaccine development), diagnostic testing, and treatment (via neutralizing Abs)). Finally, advanced immunization strategies against COVID-19 are discussed along with the contemporary circumstances and future challenges.

Plaque Reduction Neutralization Test (PRNT) Accuracy in Evaluating Humoral Immune Response to SARS-CoV-2

Massive vaccination positively impacted the SARS-CoV-2 pandemic, being a strategy to increase the titers of neutralizing antibodies (NAbs) in the population. Assessing NAb levels and understanding the kinetics of NAb responses is critical for evaluating immune protection. In this study, we optimized and validated a PRNT50 assay to assess 50% virus neutralization and evaluated its accuracy to measure NAbs to the original strain or variant of SARS-CoV-2. The optimal settings were selected, such as the cell (2 × 105 cells/well) and CMC (1.5%) concentrations and the viral input (~60 PFU/well) for PRNT-SARS-CoV-2 with cut-off point = 1.64 log5 based on the ROC curve (AUC = 0.999). The validated PRNT-SARS-CoV-2 assay presented high accuracy with an intraassay precision of 100% for testing samples with different NAb levels (low, medium, and high titers). The method displays high selectivity without cross-reactivity with dengue (DENV), measles (MV), zika (ZIKV), and yellow fever (YFV) viruses. In addition, the standardized PRNT-SARS-CoV-2 assay presented robustness when submitted to controlled variations. The validated PRNT assay was employed to test over 1000 specimens from subjects with positive or negative diagnoses for SARS-CoV-2 infection. Patients with severe COVID-19 exhibited higher levels of NAbs than those presenting mild symptoms for both the Wuhan strain and Omicron. In conclusion, this study provides a detailed description of an optimized and validated PRNT50 assay to monitor immune protection and to subsidize surveillance policies applied to epidemiologic studies of COVID-19.

Population-based study of the durability of humoral immunity after SARS-CoV-2 infection

SARS-CoV-2 antibody quantity and quality are key markers of humoral immunity. However, there is substantial uncertainty about their durability. We investigated levels and temporal change of SARS-CoV-2 antibody quantity and quality. We analyzed sera (8 binding, 4 avidity assays for spike-(S-)protein and nucleocapsid-(N-)protein; neutralization) from 211 seropositive unvaccinated participants, from the population-based longitudinal TiKoCo study, at three time points within one year after infection with the ancestral SARS-CoV-2 virus. We found a significant decline of neutralization titers and binding antibody levels in most assays (linear mixed regression model, p<0.01). S-specific serum avidity increased markedly over time, in contrast to N-specific. Binding antibody levels were higher in older versus younger participants - a difference that disappeared for the asymptomatic-infected. We found stronger antibody decline in men versus women and lower binding and avidity levels in current versus never-smokers. Our comprehensive longitudinal analyses across 13 antibody assays suggest decreased neutralization-based protection and prolonged affinity maturation within one year after infection.

Profiling of SARS-CoV-2 neutralizing antibody-associated antigenic peptides signature using proteome microarray

The profile of antibodies against antigenic epitopes of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during neutralizing antibody (NAb) decay has not been clarified. Using a SARS-CoV-2 proteome microarray that contained viral antigenic peptides, we analyzed the characteristics of the humoral response in patients with coronavirus disease 19 (COVID-19) in a longitudinal study. A total of 89 patients were recruited, and 226 plasma samples were serially collected in 2020. In the antigenic peptide microarray, the level of immunoglobulin G (IgG) antibodies against peptides within the S2 subunit (S-82) and a conserved gene region in variants of interest, open reading frame protein 10 (ORF10-3), were closely associated with the presence of SARS-CoV-2 NAbs. In an independent evaluation cohort of 232 plasma samples collected from 116 COVID-19 cases in 2020, S82-IgG titers were higher in NAbs-positive samples (p = 0.002) than in NAbs-negative samples using enzyme-linked immunosorbent assay. We further collected 66 plasma samples from another cohort infected by Omicron BA.1 virus in 2022. Compared with the samples with lower S82-IgG titers, NAb titers were significantly higher in the samples with higher S82-IgG titers (p = 0.04). Our findings provide insights into the understanding of the decay-associated signatures of SARS-CoV-2 NAbs.

Point of care detection of SARS-CoV-2 antibodies and neutralisation capacity-lateral flow immunoassay evaluation compared to commercial assay to inform potential role in therapeutic and surveillance practices

Introduction

As the COVID-19 pandemic moves towards endemic status, testing strategies are being de-escalated. A rapid and effective point of care test (POCT) assessment of SARS-CoV-2 immune responses can inform clinical decision-making and epidemiological monitoring of the disease. This cross-sectional seroprevalence study of anti-SARS-CoV-2 antibodies in Irish healthcare workers assessed how rapid anti-SARS-CoV-2 antibody testing can be compared to a standard laboratory assay, discusses its effectiveness in neutralisation assessment and its uses into the future of the pandemic.

Methods

A point of care lateral flow immunoassay (LFA) detecting anti-SARS-CoV-2 spike (S)-receptor binding domain (RBD) neutralising antibodies (Healgen SARS-CoV-2 neutralising Antibody Rapid Test Cassette) was compared to the Roche Elecsys/-S anti-SARS-CoV-2 antibody assays and an in vitro surrogate neutralisation assay. A correlation between anti-spike (S), anti-nucleocapsid (N) titres, and in vitro neutralisation was also assessed.

Results

1,777 serology samples were tested using Roche Elecsys/-S anti-SARS-CoV-2 assays to detect total anti-N/S antibodies. 1,562 samples were tested using the POC LFA (including 50 negative controls), and 90 samples were tested using an in vitro ACE2-RBD binding inhibition surrogate neutralisation assay. The POCT demonstrated 97.7% sensitivity, 100% specificity, a positive predictive value (PPV) of 100%, and a negative predictive value (NPV) of 61% in comparison to the commercial assay. Anti-S antibody titres determined by the Roche assay stratified by the POC LFA result groups demonstrated statistically significant differences between the "Positive" and "Negative" LFA groups (p < 0.0001) and the "Weak Positive" and "Positive" LFA groups (p < 0.0001). No statistically significant difference in ACE2-RBD binding inhibition was demonstrated when stratified by the LFA POC results. A positive, statistically significant correlation was demonstrated between the in vitro pseudo-neutralisation assay results and anti-S antibody titres (rho 0.423, p < 0.001) and anti-N antibody titres (rho = 0.55, p < 0.0001).

Conclusion

High sensitivity, specificity, and PPV were demonstrated for the POC LFA for the detection of anti-S-RBD antibodies in comparison to the commercial assay. The LFA was not a reliable determinant of the neutralisation capacity of identified antibodies. POC LFA are useful tools in sero-epidemiology settings, pandemic preparedness and may act as supportive tools in treatment decisions through the rapid identification of anti-Spike antibodies.

Vaccine-induced antigen archiving enhances local memory CD8+ T cell responses following an unrelated viral infection

Viral and vaccine antigens persist or are archived in lymph node stromal cells (LNSC) such as lymphatic endothelial cells (LEC) and fibroblastic reticular cells (FRC). Here, we find that, during the time frame of antigen archiving, LEC apoptosis caused by a second, but unrelated, innate immune stimulus such as vaccina viral infection or CpG DNA administration boosted memory CD8+ T cells specific to the archived antigen. In contrast to "bystander" activation associated with unrelated infections, the memory CD8+ T cells specific to the vaccine archived antigen were significantly higher than memory CD8+ T cells of a different antigen specificity. Finally, the boosted memory CD8+ T cells resulted in increased protection against Listeria monocytogenes expressing the vaccine antigen, but only for the duration that the vaccine antigen was archived. These findings outline a novel mechanism by which LNSC archived antigens, in addition to bystander activation, can augment memory CD8+ T cell responses during repeated inflammatory insults.

Initial immune response after exposure to Mycobacterium tuberculosis or to SARS-COV-2: similarities and differences

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) and Coronavirus disease-2019 (COVID-19), whose etiologic agent is severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), are currently the two deadliest infectious diseases in humans, which together have caused about more than 11 million deaths worldwide in the past 3 years. TB and COVID-19 share several aspects including the droplet- and aerosol-borne transmissibility, the lungs as primary target, some symptoms, and diagnostic tools. However, these two infectious diseases differ in other aspects as their incubation period, immune cells involved, persistence and the immunopathological response. In this review, we highlight the similarities and differences between TB and COVID-19 focusing on the innate and adaptive immune response induced after the exposure to Mtb and SARS-CoV-2 and the pathological pathways linking the two infections. Moreover, we provide a brief overview of the immune response in case of TB-COVID-19 co-infection highlighting the similarities and differences of each individual infection. A comprehensive understanding of the immune response involved in TB and COVID-19 is of utmost importance for the design of effective therapeutic strategies and vaccines for both diseases.

Comparison of anti-spike IgG, anti-spike IgA levels and neutralizing antibody activity induced by CoronaVac and BNT162b2 vaccines in patients with inflammatory rheumatic diseases receiving immunosuppressive therapy

BACKGROUND

The importance of COVID-19 vaccination for patients on immunosuppressive (IS) medication has increased due to the high risk of severe disease or mortality. Different vaccines have varying efficacy rates against symptomatic COVID-19, ranging from 46.8% to 95%. The objective of this study was to examine the differences in anti-Spike IgG, anti-Spike IgA, and neutralizing antibody (NAb) activity between the inactive CoronaVac vaccine and the mRNA-based BNT162b2 vaccine in IS patients.

METHOD

A total of 441 volunteers, including 104 IS patients, 263 healthy controls (HC), who received two doses of CoronaVac or BNT162b2, and 74 unvaccinated patients with a history of SARS-CoV-2 infection, were included in the study. Anti-spike IgG, IgA, and NAb activity were investigated.

RESULTS

Immunogenicity with BNT162b2 was higher than with CoronaVac, but in IS groups, it was lower than HC (CoronaVac-IS: 79.3%, CoronaVac-HC: 96.5%, p < 0.001; BNT162b2-IS: 91.3%, BNT162b2-HC: 100%, p = 0.005). With CoronaVac, anti-Spike IgG levels were significantly lower than BNT162b2 (CoronaVac-IS: 234.5AU/mL, CoronaVac-HC: 457.85AU/mL; BNT162b2-IS: 5311.2AU/mL, BNT162b2-HC: 8842.8AU/mL). NAb activity in the BNT162b2 group was significantly higher. NAb and anti-Spike IgG levels were found to be correlated. Among the IS group, a significantly lower response to the vaccines was observed when using rituximab. IgA levels were found to be lower with CoronaVac.

CONCLUSIONS

Although immunogenicity was lower in IS patients, an acceptable response was obtained with both vaccines, and significantly higher anti-Spike IgG, anti-Spike IgA, and NAb activity levels were obtained with BNT162b2.

Determining clinical biomarkers to predict long-term SARS-CoV-2 antibody response among COVID-19 patients in Bangladesh

Background

Information on antibody responses following SARS-CoV-2 infection, including the magnitude and duration of responses, is limited. In this analysis, we aimed to identify clinical biomarkers that can predict long-term antibody responses following natural SARS-CoV-2 infection.

Methodology

In this prospective study, we enrolled 100 COVID-19 patients between November 2020 and February 2021 and followed them for 6 months. The association of clinical laboratory parameters on enrollment, including lactate dehydrogenase (LDH), neutrophil-lymphocyte ratio (NLR), C-reactive protein (CRP), ferritin, procalcitonin (PCT), and D-dimer, with predicting the geometric mean (GM) concentration of SARS-CoV-2 receptor-binding domain (RBD)-specific IgG antibody at 3 and 6 months post-infection was assessed in multivariable linear regression models.

Result

The mean ± SD age of patients in the cohort was 46.8 ± 14 years, and 58.8% were male. Data from 68 patients at 3 months follow-up and 55 patients at 6 months follow-up were analyzed. Over 90% of patients were seropositive against RBD-specific IgG till 6 months post-infection. At 3 months, for any 10% increase in absolute lymphocyte count and NLR, there was a 6.28% (95% CI: 9.68, -2.77) decrease and 4.93% (95% CI: 2.43, 7.50) increase, respectively, in GM of IgG concentration, while any 10% increase for LDH, CRP, ferritin, and procalcitonin was associated with a 10.63, 2.87, 2.54, and 3.11% increase in the GM of IgG concentration, respectively. Any 10% increase in LDH, CRP, and ferritin was similarly associated with an 11.28, 2.48, and 3.0% increase in GM of IgG concentration at 6 months post-infection.

Conclusion

Several clinical biomarkers in the acute phase of SARS-CoV-2 infection are associated with enhanced IgG antibody response detected after 6 months of disease onset. The measurement of SARS-CoV-2 specific antibody responses requires improved techniques and is not feasible in all settings. Baseline clinical biomarkers can be a useful alternative as they can predict antibody response during the convalescence period. Individuals with an increased level of NLR, CRP, LDH, ferritin, and procalcitonin may benefit from the boosting effect of vaccines. Further analyses will determine whether biochemical parameters can predict RBD-specific IgG antibody responses at later time points and the association of neutralizing antibody responses.

Severe Acute Respiratory Syndrome Coronavirus 2 Neutralizing Antibody Responses After Community Infections in Children and Adults

Background

We compared postinfection severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) neutralizing antibody (nAb) responses among children and adults while the D614G-like strain and Alpha, Iota, and Delta variants circulated.

Methods

During August 2020-October 2021, households with adults and children were enrolled and followed in Utah, New York City, and Maryland. Participants collected weekly respiratory swabs that were tested for SARS-CoV-2 and had sera collected during enrollment and follow-up. Sera were tested for SARS-CoV-2 nAb by pseudovirus assay. Postinfection titers were characterized with biexponential decay models.

Results

Eighty participants had SARS-CoV-2 infection during the study (47 with D614G-like virus, 17 with B.1.1.7, and 8 each with B.1.617.2 and B.1.526 virus). Homologous nAb geometric mean titers (GMTs) trended higher in adults (GMT = 2320) versus children 0-4 (GMT = 425, P = .33) and 5-17 years (GMT = 396, P = .31) at 1-5 weeks postinfection but were similar from 6 weeks. Timing of peak titers was similar by age. Results were consistent when participants with self-reported infection before enrollment were included (n = 178).

Conclusions

The SARS-CoV-2 nAb titers differed in children compared to adults early after infection but were similar by 6 weeks postinfection. If postvaccination nAb kinetics have similar trends, vaccine immunobridging studies may need to compare nAb responses in adults and children 6 weeks or more after vaccination.

Dynamics of SARS-CoV-2 Antibody Responses up to 9 Months Post-Vaccination in Individuals with Previous SARS-CoV-2 Infection Receiving Inactivated Vaccines

Humoral immunity confers protection against COVID-19. The longevity of antibody responses after receiving an inactivated vaccine in individuals with previous SARS-CoV-2 infection is unclear. Plasma samples were collected from 58 individuals with previous SARS-CoV-2 infection and 25 healthy donors (HDs) who had been vaccinated with an inactivated vaccine. The neutralizing antibodies (NAbs) and S1 domain-specific antibodies against the SARS-CoV-2 wild-type and Omicron strains and nucleoside protein (NP)-specific antibodies were measured using a chemiluminescent immunoassay. Statistical analysis was performed using clinical variables and antibodies at different timepoints after SARS-CoV-2 vaccination. NAbs targeting the wild-type or Omicron strain were detected in individuals with previous SARS-CoV-2 infection at 12 months after infection (wild-type: 81%, geometric mean (GM): 20.3 AU/mL; Omicron: 44%, GM: 9.4 AU/mL), and vaccination provided further enhancement of these antibody levels (wild-type: 98%, GM: 53.3 AU/mL; Omicron: 75%, GM: 27.8 AU/mL, at 3 months after vaccination), which were significantly higher than those in HDs receiving a third dose of inactivated vaccine (wild-type: 85%, GM: 33.6 AU/mL; Omicron: 45%, GM: 11.5 AU/mL). The level of NAbs in individuals with previous infection plateaued 6 months after vaccination, but the NAb levels in HDs declined continuously. NAb levels in individuals with previous infection at 3 months post-vaccination were strongly correlated with those at 6 months post-vaccination, and weakly correlated with those before vaccination. NAb levels declined substantially in most individuals, and the rate of antibody decay was negatively correlated with the neutrophil-to-lymphocyte ratio in the blood at discharge. These results suggest that the inactivated vaccine induced robust and durable NAb responses in individuals with previous infection up to 9 months after vaccination.

Effects of vaccines on clinical characteristics of convalescent adult patients infected with SARS-CoV-2 Omicron variant: A retrospective study

Introduction

The protective effect of SARS-CoV-2 vaccines has become a global focus due to Omicron variant pandemic. The effects of various SARS-CoV-2 vaccines are diverse. However, studies on the effect of domestic vaccines on clinical characteristics in convalescent adult patients infected with the Omicron variant are lacking.

Methods

In this retrospective, single-center cohort study, the effect of three domestic vaccines on clinical characteristics of convalescent adult patients infected with the Omicron variant was investigated in the initial largest outbreak of the Omicron variant infection between January and February 2022 in Tianjin, China. The primary endpoint was COVID-19 severity and the secondary endpoints were re-positive results on nucleic acid tests, liver and kidney function, and inflammation levels during recovery.

Results

A total of 320 adult patients infected with the Omicron variant were enrolled, including 296 post-vaccination and 24 unvaccinated patients. The median age of the unvaccinated patients was higher than that of vaccinated patients, but no significant difference was detected in the sex composition ratio between the different groups. Binary logistic regression results suggested that Sinopharm and Sinovac vaccine was an independent protective factor for relieving the severity of the Omicron variant infection. Regrettably, the vaccines did not showed any protective effect on the liver and kidney function of convalescent adult patients. Three domestic vaccines significantly relieved inflammation and increased the SARS-CoV-2-specific antibody levels. Furthermore, Sinovac and CanSino vaccines had a better immune stimulation effect on increasing T lymphocytes levels in convalescent adult patients. In addition, three domestic vaccines have protective effects on preventing re-detectable positive (RP) result in convalescent adult patients.

Conclusion

Although the three domestic vaccines cannot prevent the infection of the Omicron variant, it has a significant protective effect in adult patients. This study supports the policy of accelerating to vaccination worldwide combat the evolving and mutating SARS-CoV-2.

Discussion

Omicron spreads faster and might escape antibodies more readily than previous variants, increasing the cases of reinfection and breakthrough infections in vaccinated people. Although vaccinated people are likely to have a much lower risk of severe disease from Omicron infection, many issues still need to be considered. Concerns about lower vaccine efficacy because of new variants might have changed our understanding of the COVID-19 endgame, disabusing the world of the notion that global vaccination is by itself adequate for controlling SARS-CoV-2 infection. The current data showed that vaccination with three domestic SARS-CoV-2 vaccines alleviates the disease severity of adult patients with COVID-19, reduces the inflammation level and the RP rate of convalescent adult patients, and enhances body’s defense against the virus in convalescent adult patients. Moreover, our study has highlighted that a combination prevention approach of vaccination and public health measures would be an effective strategy.

Dynamics of Antibody Responses after Asymptomatic and Mild to Moderate SARS-CoV-2 Infections: Real-World Data in a Resource-Limited Country

The dynamics of humoral immune responses of patients after SARS-CoV-2 infection is unclear. This study prospectively observed changes in anti-receptor binding domain immunoglobulin G (anti-RBD IgG) and neutralizing antibodies against the Wuhan and Delta strains at 1, 3, and 6 months postinfection between October 2021 and May 2022. Demographic data, clinical characteristics, baseline parameters, and blood samples of participants were collected. Of 5059 SARS-CoV-2 infected adult patients, only 600 underwent assessment at least once between 3 and 6 months after symptom onset. Patients were categorized as immunocompetent (n = 566), immunocompromised (n = 14), or reinfected (n = 20). A booster dose of a COVID-19 vaccine was strongly associated with maintained or increased COVID-19 antibody levels. The booster dose was also more strongly associated with antibody responses than the primary vaccination series. Among patients receiving a booster dose of a mRNA vaccine or a heterologous regimen, antibody levels remained steady or even increased for 3 to 6 months after symptom onset compared with inactivated or viral vector vaccines. There was a strong correlation between anti-RBD IgG and neutralizing antibodies against the Delta variant. This study is relevant to resource-limited countries for administering COVID-19 vaccines 3 to 6 months after infection.

Humoral SARS-CoV-2 Immune Response in COVID-19 Recovered Vaccinated and Unvaccinated Individuals Related to Post-COVID-Syndrome

BACKGROUND

The duration of anti-SARS-CoV-2-antibody detectability up to 12 months was examined in individuals after either single convalescence or convalescence and vaccination. Moreover, variables that might influence an anti-RBD/S1 antibody decline and the existence of a post-COVID-syndrome (PCS) were addressed.

METHODS

Forty-nine SARS-CoV-2-qRT-PCR-confirmed participants completed a 12-month examination of anti-SARS-CoV-2-antibody levels and PCS-associated long-term sequelae. Overall, 324 samples were collected. Cell-free DNA (cfDNA) was isolated and quantified from EDTA-plasma. As cfDNA is released into the bloodstream from dying cells, it might provide information on organ damage in the late recovery of COIVD-19. Therefore, we evaluated cfDNA concentrations as a biomarker for a PCS. In the context of antibody dynamics, a random forest-based logistic regression with antibody decline as the target was performed and internally validated.

RESULTS

The mean percentage dynamic related to the maximum measured value was 96 (±38)% for anti-RBD/S1 antibodies and 30 (±26)% for anti-N antibodies. Anti-RBD/S1 antibodies decreased in 37%, whereas anti-SARS-CoV-2-anti-N antibodies decreased in 86% of the subjects. Clinical anti-RBD/S1 antibody decline prediction models, including vascular and other diseases, were cross-validated (highest AUC 0.74). Long-term follow-up revealed no significant reduction in PCS prevalence but an increase in cognitive impairment, with no indication for cfDNA as a marker for a PCS.

CONCLUSION

Long-term anti-RBD/S1-antibody positivity was confirmed, and clinical parameters associated with declining titers were presented. A fulminant decrease in anti-SARS-CoV-2-anti-N antibodies was observed (mean change to maximum value 30 (±26)%). Anti-RBD/S1 antibody titers of SARS-CoV-2 recovered subjects boosted with a vaccine exceeded the maximum values measured after single infection by 235 ± 382-fold, with no influence on preexisting PCS. PCS long-term prevalence was 38.6%, with an increase in cognitive impairment compromising the quality of life. Quantified cfDNA measured in the early post-COVID-19 phase might not be an effective marker for PCS identification.

Validation of a SARS-CoV-2 Surrogate Virus Neutralization Test in Recovered and Vaccinated Healthcare Workers

Vaccination against COVID-19 is the main public health approach to fight against the pandemic. The Spike (S) glycoprotein of SARS-CoV-2 is the principal target of the neutralizing humoral response. We evaluated the analytical and clinical performances of a surrogate virus neutralization test (sVNT) compared to conventional neutralization tests (cVNTs) and anti-S eCLIA assays in recovered and/or vaccinated healthcare workers. Our results indicate that sVNTs displayed high specificity and no cross-reactivity. Both eCLIA and sVNT immunoassays were good at identifying cVNT serum dilutions ≥1:16. The optimal thresholds when identifying cVNT titers ≥1:16, were 74.5 U/mL and 49.4 IU/mL for anti-S eCLIA and sVNT, respectively. Our data show that neutralizing antibody titers (Nab) differ from one individual to another and may diminish over time. Specific assays such as sVNTs could offer a reliable complementary tool to routine anti-S serological assays.

SARS-CoV-2 epidemiology, antibody dynamics, and neutralisation capacity in Irish healthcare workers in the era of booster COVID-19 vaccinations

Background

The PRECISE Study, a multi-phase cross-sectional seroprevalence study of anti-SARS-CoV-2 antibodies in Irish healthcare workers (HCW) investigated: (1) risk factors for SARS-CoV-2 seropositivity, (2) the durability of antibody responses in a highly vaccinated HCW cohort, and (3) the neutralisation capacity of detected antibodies, prior to booster COVID-19 vaccination.

Materials and methods

Serology samples were collected across two hospital sites in November 2021 and analysed using the Roche Elecsys Anti-SARS-CoV-2/Elecsys-S Anti-SARS-CoV-2 assays to detect anti-nucleocapsid (N) and anti-spike (S) antibodies respectively. Paired serology results from prior study phases were used to analyse changes in individual HCW serostatus over time. Risk-factors for SARS-CoV-2 infection were assessed for demographic and work-related factors. Antibody neutralisation capacity was assessed in a subset of samples via an in vitro ACE2 binding enzyme-linked immunosorbent assay.

Results

2,344 HCW samples were analysed. Median age was 43 years (IQR 33-50) with 80.5% (n = 1,886) female participants. Irish (78.9%, n = 1,850) and Asian (12.3%, n = 288) were the most commonly reported ethnicities. Nursing/midwifery (39.3%, n = 922) was the most common job role. 97.7% of participants were fully vaccinated, with Pfizer (81.1%, n = 1,902) and AstraZeneca (16.1%, n = 377) the most common vaccines received. Seroprevalence for anti-SARS-CoV-2 antibodies indicating prior infection was 23.4%, of these 33.6% represented previously undiagnosed infections. All vaccinated participants demonstrated positive anti-S antibodies and in those with paired serology, no individual demonstrated loss of previously positive anti-S status below assay threshold for positivity. Interval loss of anti-N antibody positivity was demonstrated in 8.8% of previously positive participants with paired results. Risk factors for SARS-CoV-2 seropositivity suggestive of previous infection included age 18-29 years (aRR 1.50, 95% CI 1.19-1.90, p < 0.001), India as country of birth (aRR 1.35, 95% CI 1.01-1.73, p = 0.036), lower education level (aRR 1.35, 95% CI 1.11-1.66, p = 0.004) and HCA job role (aRR 2.12, 95% CI 1.51-2.95, p < 0.001). Antibody neutralisation varied significantly by anti-SARS-CoV-2 antibody status, with highest levels noted in those anti-N positive, in particular those with vaccination plus previous SARS-CoV-2 infection.

Conclusion

All vaccinated HCWs maintained anti-S positivity prior to COVID-19 booster vaccination, however anti-N positivity was more dynamic over time. Antibody neutralisation capacity was highest in participants with COVID-19 vaccination plus prior SARS-CoV-2 infection.

Maternal Antibody Response and Transplacental Transfer Following Severe Acute Respiratory Syndrome Coronavirus 2 Infection or Vaccination in Pregnancy

BACKGROUND

Pregnant persons are at increased risk of severe coronavirus disease 2019 (COVID-19) and adverse obstetric outcomes. Understanding maternal antibody response, duration, and transplacental transfer after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and COVID-19 vaccination is important to inform public health recommendations.

METHODS

This prospective observational cohort study included 351 pregnant people who had SARS-CoV-2 infection or COVID-19 vaccination during pregnancy. Immunoglobulin (Ig) G and IgM to SARS-CoV-2 S1 receptor binding domain were measured in maternal and cord blood. Antibody levels and transplacental transfer ratios were compared across (1) disease severity for those with SARS-CoV-2 infection and (2) infection versus vaccination.

RESULTS

There were 252 individuals with SARS-CoV-2 infection and 99 who received COVID-19 vaccination during pregnancy. Birthing people with more severe SARS-CoV-2 infection had higher maternal and cord blood IgG levels (P = .0001, P = .0001). Median IgG transfer ratio was 0.87-1.2. Maternal and cord blood IgG were higher after vaccination than infection (P = .001, P = .001). Transfer ratio was higher after 90 days in the vaccinated group (P < .001). Modeling showed higher amplitude and half-life of maternal IgG following vaccination (P < .0001). There were no significant differences by fetal sex.

CONCLUSIONS

COVID-19 vaccination in pregnancy leads to higher and longer lasting maternal IgG levels, higher cord blood IgG, and higher transfer ratio after 90 days compared with SARS-CoV-2 infection. Greater infection severity leads to higher maternal and cord blood antibodies. Maternal IgG decreases over time following both vaccination and infection, reinforcing the importance of vaccination, even after infection, and vaccine boosters for pregnant patients.

Humoral and Cellular Response of Transplant Recipients to a Third Dose of mRNA SARS-CoV-2 Vaccine: A Systematic Review and Meta-analysis

BACKGROUND

High rates of nonresponse to 2 doses of mRNA severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine have been reported in transplant recipients. Several studies have investigated the efficacy of a third dose in this population. However, efficacy remains unclear, as response rates vary across studies. Therefore, we conducted a systematic review and meta-analysis to determine the efficacy of a third dose of any mRNA SARS-CoV-2 vaccine in transplant recipients.

METHODS

Preferred Reporting Items for Systematic Review and Meta-Analysis reporting guidelines (PROSPERO:CRD42021281498) were followed. Medline, Embase, and CENTRAL were searched from inception to December 2, 2021, without restrictions. All full-text studies reporting on the efficacy of a third dose of any mRNA SARS-CoV-2 vaccine in pediatric and adult transplant recipients were included. The National Institutes of Health quality assessment tool for case series and the Cochrane risk of bias tool determined study quality. Meta-analysis was performed via the DerSimonian-Laird random-effect model.

RESULTS

Of 84 records, 12 studies totaling 1257 patients met inclusion criteria. One study was a randomized controlled trial, whereas all other studies were observational. Across 7 studies (801 patients), humoral response after 3 doses was observed in 66.1% (95% confidence interval, 62.8%-69.4%; I2 = 0%) of transplant recipients. Triple immunosuppression, mycophenolate, antiproliferatives, and belatacept use were associated with reduced odds of humoral response in studies reporting multivariate analyses. Transplant recipients receiving a third dose displayed higher levels of neutralizing antibodies to SARS-CoV-2 variants (Alpha, Beta, and Delta) compared with placebo.

CONCLUSIONS

A third dose SARS-CoV-2 mRNA vaccine should be strongly considered in transplant recipients. Limitations included lack of controlled studies and clinically relevant thresholds to determine response to vaccination.

Immune response and safety of inactivated SARS-CoV-2 vaccines during pregnancy: a real-world observational study

BACKGROUND

As pregnant women are excluded from clinical trials of inactivated SARS-CoV-2 vaccines, it is important to assess the immune response in women receiving the vaccination while unknowingly pregnant.

METHODS

In a multicenter cross-sectional study, we enrolled 873 pregnant women aged 18-45 years. Serum antibody levels induced by inactivated vaccines were determined. Adverse events were collected by self-reported survey after vaccination. Logistic regression model and restricted cubic spline model were used to investigate the association of factors with antibody positivity.

RESULTS

As the doses of the vaccine increase, neutralizing antibody (NAb) positivity was 98.3%, 39.5%, and 9.5% in pregnant women, respectively. The dose of vaccine and duration since vaccination were associated with NAb positivity. The OR of two and three doses of vaccines were 7.20 and 458.33 (P < 0.05). NAb levels and duration since vaccination showed a linear relationship in pregnant women vaccinated two doses, with a decrease to a near seropositivity threshold at 22 weeks. Adverse events were mainly mild or moderate after vaccinated during pregnancy, with no increase in incidence compared with whom vaccinated during pre-pregnancy.

CONCLUSIONS

The use of inactivated vaccines during pregnancy induced favorable immune persistence, and the incidence of adverse events did not increase.

D614G SARS-CoV-2 Pseudovirus Infectivity and Binding of Spike Protein to the ACE2 Receptor Inversely Correlates with Serum SARS-CoV-2-Specific IgG Levels

Understanding the functional characteristics of antibodies produced against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) will assist in the determination of disease outcomes for this virus. In this study, the ability of antibodies to inhibit viral entry into the host cell through the interaction of the receptor binding domain of the viral spike protein and the angiotensin-converting enzyme 2 receptor on the human cell surface was investigated. The SARS-CoV-2 IgG levels in 20 SARS-CoV-2 positive patients were measured using an enzyme-linked immunosorbent assay, and the samples were further analyzed using a functional binding assay. Inhibition of viral infectivity was also measured using a pseudovirus neutralization assay against a D614G SARS-CoV-2 virus strain. A significant correlation between IgG levels and neutralizing antibody 50% inhibitory concentration (IC₅₀) titers was observed (p < 0.05). Similarly, the IC₅₀ titers obtained in the neutralization and binding assays were significantly correlated (p < 0.001). Varying levels of IgG and IC₅₀ titers were observed for the SARS-CoV-2 antibody-positive samples, with one sample not showing any neutralizing capability despite detectable IgG levels. Gender comparisons showed no statistical differences in any of the assays. These results suggest that increased SARS-CoV-2 IgG levels correlate with greater protection against the entry of the virus into cells; however, further investigations in larger studies are needed to confirm the correlates of protection.

Growth Differentiation Factor 15 (GDF-15) Levels Associate with Lower Survival in Chronic Kidney Disease Patients with COVID-19

A cytokine storm drives the pathogenesis of severe COVID-19 infection and several biomarkers have been linked to mortality. Chronic kidney disease (CKD) emerged as a risk factor for severe COVID-19. We investigated the association between selected biomarkers and mortality in 77 patients hospitalized for COVID-19, and whether they differ in patients with eGFR higher and lower than 45 mL/min. The association between patients’ characteristics, plasma biomarkers and mortality was conducted by univariate logistic regression models and independent predictors of mortality were then used to create a multivariate prediction model through Cox regression. Patients with lower eGFR had a significant increase of GDF-15, CD-25 and RAGE, with higher plasma levels in non-survivors and in patients who needed ventilation. At univariate analysis, low and mid-low GDF-15 quartiles (<4.45 ng/mL) were associated with lower mortality risk, while mid-high and high quartiles (>4.45 ng/mL) were associated with higher mortality risk. Independent association between GDF-15 quartiles and mortality risk was confirmed in the Cox model and adjusted for eGFR, age, fever and dyspnea (HR 2.28, CI 1.53−3.39, p < 0.0001). The strength of the association between GDF-15 quartiles and mortality risk increased in patients with lower compared to higher eGFR (HR 2.53, CI 1.34−4.79 versus HR 1.99, CI 1.17−3.39). Our findings may suggest a further investigation of the effect of GDF-15 signaling pathway inhibition in CKD.

Dynamics of humoral immune response in SARS-CoV-2 infected individuals with different clinical stages

Background

The COVID-19 pandemic remains a global health problem. As in other viral infections, the humoral immune response against SARS-CoV-2 is thought to be crucial for controlling the infection. However, the dynamic of B cells in the clinical spectrum of this disease is still controversial. This study aimed to characterize B cell subsets and neutralizing responses in COVID-19 patients according to disease severity through a one-month follow-up.

Methods

A cohort of 71 individuals with SARS-CoV-2 infection confirmed by RT-PCR were recruited and classified into four groups: i) asymptomatic; ii) symptomatic outpatients; iii) hospitalized in ward, and iv) intensive care unit patients (ICU). Samples were taken at days 0 (inclusion to the study), 7 and 30. B cell subsets and neutralizing antibodies were assessed using multiparametric flow cytometry and plaque reduction neutralization, respectively.

Results

Older age, male gender and body mass index over 25 were common factors among hospitalized and ICU patients, compared to those with milder clinical presentations. In addition, those requiring hospitalization had more comorbidities. A significant increase in the frequencies of CD19+ cells at day 0 was observed in hospitalized and ICU patients compared to asymptomatic and symptomatic groups. Likewise, the frequency of plasmablasts was significantly increased at the first sample in the ICU group compared to the asymptomatic group, but then waned over time. The frequency of naïve B cells decreased at days 7 and 30 compared to day 0 in hospitalized and ICU patients. The neutralizing antibody titers were higher as the severity of COVID-19 increased; in asymptomatic individuals, it was strongly correlated with the percentage of IgM+ switched memory B cells, and a moderate correlation was found with plasmablasts.

Conclusion

The humoral immune response is variable among SARS-CoV-2 infected people depending on the severity and time of clinical evolution. In severe COVID-19 patients, a higher plasmablast frequency and neutralizing antibody response were observed, suggesting that, despite having a robust humoral immunity, this response could be late, having a low impact on disease outcome.

Heterogenous humoral and cellular immune responses with distinct trajectories post-SARS-CoV-2 infection in a population-based cohort

To better understand the development of SARS-CoV-2-specific immunity over time, a detailed evaluation of humoral and cellular responses is required. Here, we characterize anti-Spike (S) IgA and IgG in a representative population-based cohort of 431 SARS-CoV-2-infected individuals up to 217 days after diagnosis, demonstrating that 85% develop and maintain anti-S responses. In a subsample of 64 participants, we further assess anti-Nucleocapsid (N) IgG, neutralizing antibody activity, and T cell responses to Membrane (M), N, and S proteins. In contrast to S-specific antibody responses, anti-N IgG levels decline substantially over time and neutralizing activity toward Delta and Omicron variants is low to non-existent within just weeks of Wildtype SARS-CoV-2 infection. Virus-specific T cells are detectable in most participants, albeit more variable than antibody responses. Cluster analyses of the co-evolution of antibody and T cell responses within individuals identify five distinct trajectories characterized by specific immune patterns and clinical factors. These findings demonstrate the relevant heterogeneity in humoral and cellular immunity to SARS-CoV-2 while also identifying consistent patterns where antibody and T cell responses may work in a compensatory manner to provide protection.

The persistence of the immune response to SARS-CoV-2 after recovery from infection is an indicator for subsequent protection against infection. Here the authors follow recovered patients and measure antibody and T cell responses and find that these two parts of the immune response may have different longevity.

SARS-CoV-2 antibody progression and neutralizing potential in mild symptomatic COVID-19 patients – a comparative long term post-infection study

Background

Since December 2019, SARS-CoV-2 has been keeping the world in suspense. Rapid tests, molecular diagnosis of acute infections, and vaccination campaigns with vaccines are building blocks of strategic pandemic control worldwide. For laboratory diagnostics, the quantification of the antibody titer of convalescents and vaccinated patients is thus increasingly coming to the fore.

Methods

Here we present an evaluation on the comparability of five serological tests on a cohort of 13 patients with mild COVID-19 disease. Also participants who were vaccinated after recovery were included in this study. All common immune methods (ELISA, CLIA, PETIA) and SARS-CoV-2 specific antigens (N-, S1- and RBD-) were specifically tracked and directly compared for up to 455 days. The titer of recovered participants was also set to the degree of symptoms during infection and the occurrence of Long-COVID. In addition, relative comparability of different serological tests, all standardized to WHO, was set in reference to the neutralizing potential of the corresponding participants.

Findings

The individual immune responses over 455 days after a mild SARS-CoV-2 infection remain stable, in contrast to vaccinated participants. All sero-tests reveal comparable performance and dynamics during the study and compared well to a surrogate neutralization test.

Conclusion

The information presented here will help clinicians in the daily laboratory work in the selection and evaluation of different serological tests offered. The data also will support in respect of a sero-test-based neutralization cutoff.

Two-years antibody responses following SARS-CoV-2 infection in humans: A study protocol

The long-term antibody response to the novel SARS-CoV-2 in infected patients and their residential neighborhood remains unknown in Indonesia. This information will provide insights into the antibody kinetics over a relatively long period as well as transmission risk factors in the community. We aim to prospectively observe and determine the kinetics of the anti-SARS-CoV-2 antibody for 2 years after infection in relation to disease severity and to determine the risk and protective factors of SARS CoV-2 infections in the community. A cohort of RT-PCR confirmed SARS-CoV-2 patients (case) will be prospectively followed for 2 years and will be compared to a control population. The control group comprises SARS-CoV-2 non-infected people who live within a one-kilometer radius from the corresponding case (location matching). This study will recruit at least 165 patients and 495 controls. Demographics, community variables, behavioral characteristics, and relevant clinical data will be collected. Serum samples taken at various time points will be tested for IgM anti-Spike protein of SARS-CoV-2 and IgG anti-Spike RBD of SARS-CoV-2 by using Chemiluminescent Microparticle Immunoassay (CMIA) method. The Kaplan-Meier method will be used to calculate cumulative seroconversion rates, and their association with disease severity will be estimated by logistic regression. The risk and protective factors associated with the SARS-CoV-2 infection will be determined using conditional (matched) logistic regression and presented as an odds ratio and 95% confidence interval.

Kinetics of neutralizing antibodies against SARS-CoV-2 infection according to sex, age, and disease severity

Knowledge of the factors affecting the difference in kinetics and longevity of the neutralizing antibody (nAb) response to SARS-CoV-2 is necessary to properly prioritize vaccination. In the present study, from March to December 2020, of the 143 patients who recovered from COVID-19, 87 underwent study visits scheduled every 3 months. Patient demographics and blood samples were collected followed by a plaque reduction neutralization test to analyze nAb titers. A linear mixed model was used to compare the effects of sex, age, and disease severity over time. Results demonstrated a gradual reduction in nAb titers over time with a significant decrease from 6 to 9 months post-COVID-19 infection (p < 0.001). In time-to-sex, age, and disease severity comparisons, reduction in nAb titers over time was unaffected by sex (p = 0.167), age (p = 0.188), or disease severity (p = 0.081). Additionally, the nAb titer was 1.46 times significantly higher in those aged ≥ 50 years than in those aged < 50 years (p = 0.036) irrespective of time Moreover, the nAb titer was 2.41 times higher in the moderate or above than that in the below moderate disease severity group (p < 0.001). However, no significant differences were observed in terms of sex (p = 0.300). Given the reduction in nAbs over time, maintaining protective neutralizing antibodies regardless of sex, age, or disease severity is needed.

Recent Advances in Understanding SARS-CoV-2 Infection and Updates on Potential Diagnostic and Therapeutics for COVID-19

Abstract:

A more focused approach is needed to understand the SARS-CoV-2 virulence, structure, and genomics to devise more effective diagnostic and treatment interventions as this virus can evade the immune attack and causes life-threatening complications such as cytokine storm. The spread of the virus is still amplifying and causing thousands of new cases worldwide. It is essential to review current diagnostics and treatment approaches to pave the way to correct or modify our current practices to make more effective interventions against COVID-19. COVID-19 vaccine development has moved at a breakneck pace since the outbreak began, utilizing practically all possible platforms or tactics to ensure the success of vaccines. A total of 42 vaccine candidates have already entered clinical trials, including promising results from numerous vaccine candidates in phase 1 or phase 2 trials. Further, many existing drugs are being explored on broad-spectrum antiviral medications for their use in clinical recovery against COVID- 19. The present review attempts to re-examine the SARS-CoV-2 structure, its viral life cycle, clinical symptoms and pathogenesis, mode of transmission, diagnostics, and treatment strategies that may be useful for resorting to more effective approaches for controlling COVID-19. Various antiviral drugs and vaccination strategies with their strengths and weaknesses are also discussed in the paper to augment our understanding of COVID-19 management.

The humoral response and antibodies against SARS-CoV-2 infection

Two and a half years into the COVID-19 pandemic, we have gained many insights into the human antibody response to the causative SARS-CoV-2 virus. In this Review, we summarize key observations of humoral immune responses in people with COVID-19, discuss key features of infection- and vaccine-induced neutralizing antibodies, and consider vaccine designs for inducing antibodies that are broadly protective against different variants of the SARS-CoV-2 virus.

Longitudinal kinetics of RBD+ antibodies in COVID-19 recovered patients over 14 months

We describe the longitudinal kinetics of the serological response in COVID-19 recovered patients over a period of 14 months. The antibody kinetics in a cohort of 192 recovered patients, including 66 patients for whom follow-up serum samples were obtained at two to four clinic visits, revealed that RBD-specific antibodies decayed over the 14 months following the onset of symptoms. The decay rate was associated with the robustness of the response in that antibody levels that were initially highly elevated after the onset of symptoms subsequently decayed more rapidly. An exploration of the differences in the longitudinal kinetics between recovered patients and naïve vaccinees who had received two doses of the BNT162b2 vaccine showed a significantly faster decay in the naïve vaccinees, indicating that serological memory following natural infection is more robust than that following to vaccination. Our data highlighting the differences between serological memory induced by natural infection vs. vaccination contributed to the decision-making process in Israel regarding the necessity for a third vaccination dose.

The fundamental idea guiding vaccine science is that an ideal vaccine should induce immunity similar to the immunity produced by natural infection. A vaccine is designed to “train” the immune system in a way that it will mimic the stimulation necessary for immune development, yet not produce active disease. Understanding the persistence of antibodies in patients following recovery from natural infection with SARS-CoV-2 will help to highlight the differences between the breadth of the antibody responses following natural infection and vaccination and may inform us whether the vaccine “training” will effectively stimulate the immune system to provide long-lasting immunity. Using samples collected from recovered COVID-19 patients over an extended period of 14 months, we followed the persistence of antibodies and found an association between the antibody levels in proximity to recovery and the rate of decay. In addition, we found that the decay rate of antibodies in BNT162b2 vaccinees was significantly faster than that in recovered patients, suggesting that there are fundamental differences between the mechanisms of activation of the adaptive arm of the immune response following vaccine and natural infection. While natural infection involves full systemic activation, this activation may be incomplete with an mRNA vaccination, thereby affecting the capacity of the immune system to maintain an antibody reservoir over time.

Intranasal administration of a recombinant RBD vaccine induces long-term immunity against Omicron-included SARS-CoV-2 variants

The outbreak of coronavirus disease 2019 (COVID-19) has posed great threats to global health and economy. Several effective vaccines are available now, but additional booster immunization is required to retain or increase the immune responses owing to waning immunity and the emergency of new variant strains. The deficiency of intramuscularly delivered vaccines to induce mucosal immunity urged the development of mucosal vaccines. Here, we developed an adjuvanted intranasal RBD vaccine and monitored its long-term immunogenicity against both wild-type and mutant strains of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), including Omicron variants, in mice. Three-dose intranasal immunization with this vaccine induced and maintained high levels of neutralizing IgG antibodies in the sera for at least 1 year. Strong mucosal immunity was also provoked, including mucosal secretory IgA and lung-resident memory T cells (T_RM). We also demonstrated that the long-term persistence of lung T_RM cells is a consequence of local T-cell proliferation, rather than T-cell migration from lymph nodes. Our data suggested that the adjuvanted intranasal RBD vaccine is a promising vaccine candidate to establish robust, long-lasting, and broad protective immunity against SARS-CoV-2 both systemically and locally.

Antibody Duration After Infection From SARS-CoV-2 in the Texas Coronavirus Antibody Response Survey

Understanding the duration of antibodies to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus that causes COVID-19 is important to controlling the current pandemic. Participants from the Texas Coronavirus Antibody Response Survey (Texas CARES) with at least 1 nucleocapsid protein antibody test were selected for a longitudinal analysis of antibody duration. A linear mixed model was fit to data from participants (n = 4553) with 1 to 3 antibody tests over 11 months (1 October 2020 to 16 September 2021), and models fit showed that expected antibody response after COVID-19 infection robustly increases for 100 days postinfection, and predicts individuals may remain antibody positive from natural infection beyond 500 days depending on age, body mass index, smoking or vaping use, and disease severity (hospitalized or not; symptomatic or not).

Longitudinal Analysis of Coronavirus-Neutralizing Activity in COVID-19 Patients

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic has now been continuing for more than two years. The infection causes COVID-19, a disease of the respiratory and cardiovascular system of variable severity. Here, the humoral immune response of 80 COVID-19 patients from the University Hospital Frankfurt/Main, Germany, was characterized longitudinally. The SARS-CoV-2 neutralization activity of serum waned over time. The neutralizing potential of serum directed towards the human alpha-coronavirus NL-63 (NL63) also waned, indicating that no cross-priming against alpha-coronaviruses occurred. A subset of the recovered patients (n = 13) was additionally vaccinated with the mRNA vaccine Comirnaty. Vaccination increased neutralization activity against SARS-CoV-2 wild-type (WT), Delta, and Omicron, although Omicron-specific neutralization was not detectable prior to vaccination. In addition, the vaccination induced neutralizing antibodies against the more distantly related SARS-CoV-1 but not against NL63. The results indicate that although SARS-CoV-2 humoral immune responses induced by infection wane, vaccination induces a broad neutralizing activity against multiple SARS-CoVs, but not to the common cold alpha-coronavirus NL63.

What Is the Antibody Response and Role in Conferring Natural Immunity After SARS-CoV-2 Infection? Rapid, Living Practice Points From the American College of Physicians (Version 2)

DESCRIPTION

The Scientific Medical Policy Committee (SMPC) of the American College of Physicians (ACP) developed these living, rapid practice points to summarize the current best available evidence on the antibody response to SARS-CoV-2 infection and protection against reinfection with SARS-CoV-2. This is version 2 of the ACP practice points, which serves to update version 1, published on 16 March 2021. These practice points do not evaluate vaccine-acquired immunity or cellular immunity.

METHODS

The SMPC developed this version of the living, rapid practice points based on an updated living, rapid, systematic review conducted by the Portland VA Research Foundation and funded by the Agency for Healthcare Research and Quality.

PRACTICE POINT 1

Do not use SARS-CoV-2 antibody tests for the diagnosis of SARS-CoV-2 infection.

PRACTICE POINT 2

Do not use SARS-CoV-2 antibody tests to predict the degree or duration of natural immunity conferred by antibodies against reinfection, including natural immunity against different variants.

RETIREMENT FROM LIVING STATUS

Although natural immunity remains a topic of scientific interest, this topic is being retired from living status given the availability of effective vaccines for SARS-CoV-2 and widespread recommendations for and prevalence of their use. Currently, vaccination is the best clinical recommendation for preventing infection, reinfection, and serious illness from SARS-CoV-2 and its variants.

INVESTIGATION AND LONG-TERM MONITORING OF THE PRESENCE OF NEUTRALIZING ANTIBODY IN PATIENTS WITH COVID-19 DISEASE OF DIFFERENT CLINICAL SEVERITY

OBJECTIVES

Understanding the immune responses elicited by SARS-CoV-2 infection is critical to public health policy and vaccine development and prevention of reinfections for COVID-19. It is important to know the neutralizing capacity of antibodies and to monitor their persistence.

METHODS

Patients with Covid-19 were divided into four groups (severe-critical, moderate, mild and asymptomatic) according to their clinical severity. Antibodies against SARS-CoV-2 Spike viral surface protein were investigated by ELISA method 3 months and 9 months after the onset of the disease. Neutralizing antibody (NAb) response was evaluated by microneutralization test. Patients who received at least two doses of COVID-19 vaccine after illness were enrolled.

RESULTS

SARS-CoV-2 IgG and NAb titers were shown to be strongly correlated with disease severity. Anti-SARS-CoV-2 IgG and neutralizing antibody levels were found to be compatible with each other. After 9 months of follow-up, both IgG and NA levels continued unabated in individuals who had the disease. In individuals who received at least two doses of the vaccine, these levels increased, except for severe-critical patients.

CONCLUSIONS

High levels of anti-SARS-CoV-2 IgG are indicative, as it is difficult to investigate NAb in routine laboratories. At the same time, it can be predicted that this period may be much longer if it continues for at least 9 months and is reinforced with vaccination. This article is protected by copyright. All rights reserved.

Persistent Antibody Responses up to 18 Months after Mild SARS-CoV-2 Infection

Background

Humoral immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may wane rapidly in persons recovered from mild coronavirus disease 2019 (COVID-19), but little is known about the longevity.

Methods

Serum samples were obtained 8, 12, and 18 months after infection from 20 patients with mild COVID-19. The binding activities of serum antibodies (IgA, IgG, and IgM) against SARS-CoV-2 antigens of the Wuhan-1 reference strain (wild-type) and the B.1.1.7, P.1, B.1.167.2, and B.1.1.529 variants were measured by enzyme-linked immunosorbent assays. Neutralizing antibody titers were measured using a cytopathic effect-based live virus neutralization assay.

Results

Serum IgA and IgG antibodies against spike or receptor-binding domain (RBD) protein of wild-type SARS-CoV-2 were detected for up to 18 months, and neutralizing antibodies persisted for 8 to 18 months after infection. However, any significant antibody responses against RBD proteins of SARS-CoV-2 variants were not observed, and median neutralizing antibody titers against the Delta variant at 8, 12, and 18 months were 8–11 fold lower than against wild-type viruses (P < .001).

Conclusions

Humoral immunity persisted for up to 18 months after SARS-CoV-2 infection in patients with mild COVID-19. Humoral immune activity against more recently circulating variants, however, was reduced in this population.

Dynamic observation of SARS-CoV-2 IgM, IgG, and neutralizing antibodies in the development of population immunity through COVID-19 vaccination

Background

Currently, mass vaccine inoculation against coronavirus disease‐2019 (COVID‐19) has been being implemented globally. Rapid and the large‐scale detection of serum neutralizing antibodies (NAbs) laid a foundation for assessing the immune response against SARS‐CoV‐2 infection and vaccine. Additional assessments include the duration of antibodies and the optimal time for a heightened immune response.

Methods

The performance of five surrogate NAbs—three chemiluminescent immunoassay (CLIA) and two enzyme‐linked immunosorbent assays (ELISAs)—and specific IgM and IgG assays were compared using COVID‐19‐vaccinated serum (n = 164). Conventional virus neutralization test (cVNT) was used as a criterion and the diagnostic agreement and correlation of the five assays were evaluated. We studied the antibody responses after the two‐dose vaccine in volunteers up to 6 months.

Results

The sensitivity and specificity of five surrogate NAb assays ranged from 84% to 100%. Our cVNT results indicated great consistency with the surrogate assays. At 28 days after primary vaccination, the seropositivities of the NAbs, IgG, and IgM were 6%, 4%, and 13%, respectively. After the booster dose, seropositivities reached 14%, 65%, and 97%, respectively. Six months after receipt of the second dose, the NAb positive rate was eventually maintained at 66%. In all COVID‐19 convalescents, patients were detected with 100% NAb sat three months after discharge.

Conclusion

COVID‐19 vaccine induced a humoral immune response lasting at least six months. Rapid serological detection was used as a proxy for identifying changes in immunity levels and as a guide to whether an individual may require a booster vaccination.

Severe Acute Respiratory Syndrome Coronavirus 2 Serology Testing - A Laboratory Primer

In 2019, an emerging coronavirus, SARS-COV-2, was first identified. In the months since, SARS-CoV-2 has become a global pandemic of unimaginable scale. In 2021, SARS-CoV-2 continues to be a huge public health burden and a dominating issue in health care. In addition, SARS-CoV-2 has placed a spotlight on laboratory medicine and its key role in infectious disease management. The SARS-CoV-2 antibody testing landscape is vast and consists of dozens of antibody tests that have received EUA. The laboratory is faced with choosing the right test, staying current with the rapidly evolving recommendations, and updating test information for clients and clinicians. This review addresses what we know about the humoral response in SARS-CoV-2 infection and how this knowledge translates into appropriate serology test choice, utility, and interpretation.

SARS-CoV-2 enzyme-linked immunosorbent assays as proxies for plaque reduction neutralisation tests

Severe acute respiratory coronavirus 2 (SARS-CoV-2) has spread globally since its emergence in 2019. Most SARS-CoV-2 infections generate immune responses leading to rising levels of immunoglobulins (Ig) M, A and G which can be detected using diagnostic tests including enzyme-linked immunosorbent assays (ELISA). Whilst implying previous SARS-CoV-2 infection, the detection of Ig by ELISA does not guarantee the presence of neutralising antibodies (NAb) that can prevent the virus infecting cells. Plaque reduction neutralisation tests (PRNT) detect NAb, but are not amenable to mass testing as they take several days and require use of SARS-CoV-2 in high biocontainment laboratories. We evaluated the ability of IgG and IgM ELISAs targeting SARS-CoV-2 spike subunit 1 receptor binding domain (S1-RBD), and spike subunit 2 (S2) and nucleocapsid protein (NP), at predicting the presence and magnitude of NAb determined by PRNT. IgG S2 + NP ELISA was 96.8% [95% CI 83.8-99.9] sensitive and 88.9% [95% CI 51.8-99.7] specific at predicting the presence of NAbs (PRNT₈₀ > 1:40). IgG and IgM S1-RBD ELISAs correlated with PRNT titre, with higher ELISA results increasing the likelihood of a robust neutralising response. The IgM S1-RBD assay can be used as a rapid, high throughput test to approximate the magnitude of NAb titre.

Persistence of SARS-CoV-2 total immunoglobulins in a series of convalescent plasma and blood donors

Background

The vast majority of COVID-19 cases both symptomatic and asymptomatic develop immunity after COVID-19 contagion. Whether lasting differences exist between infection and vaccination boosted immunity is yet to be known. The aim of this study was to determine how long total anti-SARS-CoV2 antibodies due to past infection persist in peripheral blood and whether sex, age or haematological features can influence their lasting.

Material and methods

A series of 2421 donations either of SARS-CoV-2 convalescent plasma or whole blood from 1107 repeat donors from January 2020 to March 2021 was analysed. An automated chemiluminescence immunoassay for total antibodies recognizing the nucleocapsid protein of SARS-CoV-2 in human serum and plasma was performed. Sex, age, blood group, blood cell counts and percentages and immunoglobulin concentrations were extracted from electronic recordings. Blood donation is allowed after a minimum of one-month post symptom’s relapse. Donors were 69.7% males and their average age was 46. The 250 donors who had later donations after a positive one underwent further analysis. Both qualitative (positivity) and quantitative (rise or decline of optical density regarding consecutive donations) outcomes were evaluated.

Results and discussion

In 97.6% of donors with follow-up, anti-SARS-CoV-2 protein N total antibodies remained positive at the end of a follow-up period of 12.4 weeks median time (1–46, SD = 9.65) after the first positive determination. The blood group was not related to antibody waning. Lower lymphocyte counts and higher neutrophils would help predict future waning or decay of antibodies. Most recovered donors maintain their total anti-SARS-CoV-2 N protein antibodies for at least 16 weeks (at least one month must have been awaited from infection resolution to blood donation). The 10 individuals that could be followed up longer than 40 weeks (approximately 44 weeks after symptom’s relapse) were all still positive.

SARS-CoV-2 RT-PCR positivity of individuals subsequent to completing quarantine upon entry into a country during a transmission-free period

Background

During the current coronavirus disease 2019 (COVID-19) pandemic, many countries require travellers to undergo a reverse transcription-polymerase chain reaction (RT-PCR) testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) before travelling across borders. However, in persons having recovered from COVID-19, RT-PCR positivity can persist for an extended period.

Materials and methods

We describe three cases who sought fit-to-fly certificates in Thailand during the period free of local transmission but were tested positive for RT-PCR for SARS-CoV-2. All had returned from a country with an active outbreak of COVID-19. Their clinical courses are described; positive nasopharyngeal swab samples were processed for viral isolation and whole-genome sequencing (WGS); and serology as well as neutralizing antibody were assessed. The contact tracing was carried out for determining evidence of indigenous transmission among close contacts of those three cases.

Results

All three cases were completely asymptomatic. Chest computerized tomography was not compatible with COVID-19 pneumonia; cell cultures failed to rescue replication-competent virus; WGS revealed fragmented viral genetic material from nasopharyngeal swab samples; and serological tests demonstrated stable levels of antibodies, together with the presence of neutralizing antibody, suggesting past infection with negligible transmission risk. Contact tracing identified no transmission in high-risk close contact individuals.

Conclusion

RT-PCR positivity for SARS-CoV-2 might detect fragmented viral genome. Issuance of a travel certificate in these circumstances is problematic. Serology tests can help to define past infection. A practical acceptable set of guidelines for issuance of a COVID-19 safety travel certification is a necessity.

Genomic, immunological and clinical analysis of COVID-19 vaccine breakthrough infections in Beijing, China

As the COVID-19 pandemic is still ongoing and SARS-CoV-2 variants are circulating worldwide, an increasing number of breakthrough infections are being detected despite the good efficacy of COVID-19 vaccines. Data on 88 COVID-19 breakthrough cases (breakthrough infections group) and 41 unvaccinated cases (unvaccinated group) from 1 June to 22 August, 2021, were extracted from a cloud database established at Beijing Ditan Hospital to evaluate the clinical, immunological and genomic characteristics of COVID-19 breakthrough infections. Among these 129 COVID-19 cases, 33 whole genomes were successfully sequenced, of which 23 were Delta variants, including 15 from the breakthrough infections group. Asymptomatic and mild cases predominated in both groups, but 2 patients developed severe disease in the unvaccinated group. The median time of viral shedding in the breakthrough infections group was significantly lower than that in the unvaccinated group (P = 0.003). In the breakthrough infections group, the IgG titres showed a significantly increasing trend (P =0.007), and the CD4+ T lymphocyte count was significantly elevated (P=0.018). For people infected with the Delta variant in the two groups, no significant difference was observed in either the RT-qPCR results or viral shedding time. In conclusion, among vaccinated patients, the cases of COVID-19 vaccine breakthrough infections were mainly asymptomatic and mild, IgG titres were significantly increased and rose rapidly, and the viral shedding time was shorter. This article is protected by copyright. All rights reserved.

Characterization of SARS-CoV-2-specific humoral immunity and its potential applications and therapeutic prospects

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is an ongoing pandemic that poses a great threat to human health worldwide. As the humoral immune response plays essential roles in disease occurrence and development, understanding the dynamics and characteristics of virus-specific humoral immunity in SARS-CoV-2-infected patients is of great importance for controlling this disease. In this review, we summarize the characteristics of the humoral immune response after SARS-CoV-2 infection and further emphasize the potential applications and therapeutic prospects of SARS-CoV-2-specific humoral immunity and the critical role of this immunity in vaccine development. Notably, serological antibody testing based on the humoral immune response can guide public health measures and control strategies; however, it is not recommended for population surveys in areas with very low prevalence. Existing evidence suggests that asymptomatic individuals have a weaker immune response to SARS-CoV-2 infection, whereas SARS-CoV-2-infected children have a more effective humoral immune response than adults. The correlations between antibody (especially neutralizing antibody) titers and protection against SARS-CoV-2 reinfection should be further examined. In addition, the emergence of cross-reactions among different coronavirus antigens in the development of screening technology and the risk of antibody-dependent enhancement related to SARS-CoV-2 vaccination should be given further attention.

Cellular metabolic basis of altered immunity in the lungs of patients with COVID-19

Metabolic pathways drive cellular behavior. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection causes lung tissue damage directly by targeting cells or indirectly by producing inflammatory cytokines. However, whether functional alterations are related to metabolic changes in lung cells after SARS-CoV-2 infection remains unknown. Here, we analyzed the lung single-nucleus RNA-sequencing (snRNA-seq) data of several deceased COVID-19 patients and focused on changes in transcripts associated with cellular metabolism. We observed upregulated glycolysis and oxidative phosphorylation in alveolar type 2 progenitor cells, which may block alveolar epithelial differentiation and surfactant secretion. Elevated inositol phosphate metabolism in airway progenitor cells may promote neutrophil infiltration and damage the lung barrier. Further, multiple metabolic alterations in the airway goblet cells are associated with impaired muco-ciliary clearance. Increased glycolysis, oxidative phosphorylation, and inositol phosphate metabolism not only enhance macrophage activation but also contribute to SARS-CoV-2 induced lung injury. The cytotoxicity of natural killer cells and CD8⁺ T cells may be enhanced by glycerolipid and inositol phosphate metabolism. Glycolytic activation in fibroblasts is related to myofibroblast differentiation and fibrogenesis. Glycolysis, oxidative phosphorylation, and glutathione metabolism may also boost the aging, apoptosis and proliferation of vascular smooth muscle cells, resulting in pulmonary arterial hypertension. In conclusion, this preliminary study revealed a possible cellular metabolic basis for the altered innate immunity, adaptive immunity, and niche cell function in the lung after SARS-CoV-2 infection. Therefore, patients with COVID-19 may benefit from therapeutic strategies targeting cellular metabolism in future.

Dynamics of infection-elicited SARS-CoV-2 antibodies in children over time

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection elicits an antibody response that targets several viral proteins including spike (S) and nucleocapsid (N); S is the major target of neutralizing antibodies. Here, we assess levels of anti-N binding antibodies and anti-S neutralizing antibodies in unvaccinated children compared with unvaccinated older adults following infection. Specifically, we examine neutralization and anti-N binding by sera collected up to 52 weeks following SARS-CoV-2 infection in children and compare these to a cohort of adults, including older adults, most of whom had mild infections that did not require hospitalization. Neutralizing antibody titers were lower in children than adults early after infection, but by 6 months titers were similar between age groups. The neutralizing activity of the children's sera decreased modestly from one to six months; a pattern that was not significantly different from that observed in adults. However, infection of children induced much lower levels of anti-N antibodies than in adults, and levels of these anti-N antibodies decreased more rapidly in children than in adults, including older adults. These results highlight age-related differences in the antibody responses to SARS-CoV-2 proteins and, as vaccines for children are introduced, may provide comparator data for the longevity of infection-elicited and vaccination-induced neutralizing antibody responses.

Nine-month course of SARS-CoV-2 antibodies in individuals with COVID-19 infection

Background

The continual course of the pandemic points to the importance of studies on the rate and durability of protective immunity after infection or vaccination.

Aims

In this study, we aimed to monitor anti-nucleocapsid (N) and anti-spike (S) antibodies against SARS-CoV-2 nearly 9 months duration after infection.

Methods

Anti-nucleocapsid (N) (at 11–15-20–29-38 weeks) and anti-spike antibodies (at 11 and 38 weeks) against SARS-CoV-2 were monitored during 38 weeks after the initial symptoms of COVID-19.

Results

Of 37 cases between 18 and 57 years old, 54% were women. The findings showed that anti-N antibodies decreased significantly after the 15th week (between 15 and 20 weeks, p = 0.016; 20–29 weeks, p = 0.0009; and 29–38 weeks, p = 0.049). At the 38th week, mean antibody levels decreased 35% compared to the 11th week, and 8% of the cases turned negative results. Anti-N antibody average level was 56.48 on the 11th week (the cut-off index threshold ≥ 1). It was estimated statistically that it would decrease to an average of 20.48 in weeks 53–62. In females, average antibody levels of all measurements were lower than males (p > 0.05). Anti-S antibody levels 14% increased at 38th week compared to 11th week (quantitative positivity threshold ≥ 0.8 U/ml), and no cases were negative at 38th week.

Conclusions

Patients had ≥ 90% positivity after at least 9 months of symptoms, both anti-N and anti-S antibodies. In all samples, both anti-N and anti-S antibody levels were lower in females. The findings suggest that the quantitative values of anti-S antibodies remained high for at least 9 months and could provide protection.

Persistence of Anti-SARS-CoV-2 Antibodies in Long Term Care Residents Over Seven Months After Two COVID-19 Outbreaks

Background

As part of the public health outbreak investigations, serological surveys were carried out following two COVID-19 outbreaks in April 2020 and October 2020 in one long term care facility (LTCF) in British Columbia, Canada. This study describes the serostatus of the LTCF residents and monitors changes in their humoral response to SARS-CoV-2 and other human coronaviruses (HCoV) over seven months.

Methods

A total of 132 serum samples were collected from all 106 consenting residents (aged 54-102) post-first outbreak (N=87) and post-second outbreak (N=45) in one LTCF; 26/106 participants provided their serum following both COVID-19 outbreaks, permitting longitudinal comparisons between surveys. Health-Canada approved commercial serologic tests and a pan-coronavirus multiplexed immunoassay were used to evaluate antibody levels against the spike protein, nucleocapsid, and receptor binding domain (RBD) of SARS-CoV-2, as well as the spike proteins of HCoV-229E, HCoV-HKU1, HCoV-NL63, and HCoV-OC43. Statistical analyses were performed to describe the humoral response to SARS-CoV-2 among residents longitudinally.

Findings

Survey findings demonstrated that among the 26 individuals that participated in both surveys, all 10 individuals seropositive after the first outbreak continued to be seropositive following the second outbreak, with no reinfections identified among them. SARS-CoV-2 attack rate in the second outbreak was lower (28.6%) than in the first outbreak (40.2%), though not statistically significant (P>0.05). Gradual waning of anti-nucleocapsid antibodies to SARS-CoV-2 was observed on commercial (median Δ=-3.7, P=0.0098) and multiplexed immunoassay (median Δ=-169579, P=0.014) platforms; however, anti-spike and anti-receptor binding domain (RBD) antibodies did not exhibit a statistically significant decline over 7 months. Elevated antibody levels for beta-HCoVs OC43 (P<0.0001) and HKU1 (P=0.0027) were observed among individuals seropositive for SARS-CoV-2 compared to seronegative individuals.

Conclusion

Our study utilized well-validated serological platforms to demonstrate that humoral responses to SARS-CoV-2 persisted for at least 7 months. Elevated OC43 and HKU1 antibodies among SARS-CoV-2 seropositive individuals may be attributed to cross reaction and/or boosting of humoral response.