mRNA vaccine-elicited antibodies to SARS-CoV-2 and circulating variants.

Here we report on the antibody and memory B cell responses of a cohort of 20 volunteers who received the Moderna (mRNA-1273) or Pfizer-BioNTech (BNT162b2) vaccine against SARS-CoV-21-4. Eight weeks after the second injection of vaccine, volunteers showed high levels of IgM and IgG anti-SARS-CoV-2 spike protein (S) and receptor-binding-domain (RBD) binding titre. Moreover, the plasma neutralizing activity and relative numbers of RBD-specific memory B cells of vaccinated volunteers were equivalent to those of individuals who had recovered from natural infection5,6. However, activity against SARS-CoV-2 variants that encode E484K-, N501Y- or K417N/E484K/N501-mutant S was reduced by a small-but significant-margin. The monoclonal antibodies elicited by the vaccines potently neutralize SARS-CoV-2, and target a number of different RBD epitopes in common with monoclonal antibodies isolated from infected donors5-8. However, neutralization by 14 of the 17 most-potent monoclonal antibodies that we tested was reduced or abolished by the K417N, E484K or N501Y mutation. Notably, these mutations were selected when we cultured recombinant vesicular stomatitis virus expressing SARS-CoV-2 S in the presence of the monoclonal antibodies elicited by the vaccines. Together, these results suggest that the monoclonal antibodies in clinical use should be tested against newly arising variants, and that mRNA vaccines may need to be updated periodically to avoid a potential loss of clinical efficacy.

Optimizing haematopoietic stem and progenitor cell apheresis collection from plerixafor-mobilized patients with sickle cell disease.

We adjusted haematopoietic stem and progenitor cell (HSPC) apheresis collection from patients with sickle cell disease (SCD) by targeting deep buffy coat collection using medium or low collection preference (CP), and by increasing anticoagulant-citrate-dextrose-solution A dosage. In 43 HSPC collections from plerixafor-mobilized adult patients with SCD, we increased the collection efficiency to 35.79% using medium CP and 82.23% using low CP. Deep buffy coat collection increased red blood cell contamination of the HSPC product, the product haematocrit was 4.7% with medium CP and 6.4% with low CP. These adjustments were well-tolerated and allowed efficient HSPC collection from SCD patients.

Collection of peripheral blood mononucleated cells for chronic graft-versus-host disease immunology research: safety and effectiveness of leukapheresis in 132 patients.

BACKGROUND: Chronic graft-versus-host disease (GVHD) is a major cause of late morbidity and non-relapse mortality in recipients of allogeneic hematopoietic cell transplantation (HCT). Its biology, however, remains poorly understood, making the studies of its biology and immunomodulatory therapies a difficult task. Such research is often hampered by lymphopenia which is common in these patients and precludes studies of critical cellular subsets across the spectrum of severity of disease. This study explores the potential of leukapheresis to safely acquire and efficiently store immune cells for immunology research in chronic GVHD. METHODS: This is a cross-sectional study in which 132 consecutively accrued patients undergo optional research leukapheresis and a one-week comprehensive outpatient evaluation. Baseline clinical and laboratory data and efficiency of the procedure were reported. RESULTS: Ninety-four of 132 patients (71%) achieved the goal collection of 2 × 10^9 PBMNCs with a mean volume processed of 4.6 L. Only mild decreases in hemoglobin, platelet, lymphocyte and monocytes were observed. All adverse events were mild (grade 1) and had resolved by the time of discharge from the apheresis unit. CONCLUSION: This study demonstrates feasibility, safety, and efficiency of research leukapheresis in a frail patient population. Results presented promote leukapheresis as a standard research practice option in studies of chronic GVHD in humans which may expedite advances in our understanding of this complex multisystem disease.

Longitudinal transcriptional analysis of peripheral blood leukocytes in COVID-19 convalescent donors.

BACKGROUND: SARS-CoV2 can induce a strong host immune response. Many studies have evaluated antibody response following SARS-CoV2 infections. This study investigated the immune response and T cell receptor diversity in people who had recovered from SARS-CoV2 infection (COVID-19). METHODS: Using the nCounter platform, we compared transcriptomic profiles of 162 COVID-19 convalescent donors (CCD) and 40 healthy donors (HD). 69 of the 162 CCDs had two or more time points sampled. RESULTS: After eliminating the effects of demographic factors, we found extensive differential gene expression up to 241 days into the convalescent period. The differentially expressed genes were involved in several pathways, including virus-host interaction, interleukin and JAK-STAT signaling, T-cell co-stimulation, and immune exhaustion. A subset of 21 CCD samples was found to be highly "perturbed," characterized by overexpression of PLAU, IL1B, NFKB1, PLEK, LCP2, IRF3, MTOR, IL18BP, RACK1, TGFB1, and others. In addition, one of the clusters, P1 (n = 8) CCD samples, showed enhanced TCR diversity in 7 VJ pairs (TRAV9.1_TCRVA_014.1, TRBV6.8_TCRVB_016.1, TRAV7_TCRVA_008.1, TRGV9_ENST00000444775.1, TRAV18_TCRVA_026.1, TRGV4_ENST00000390345.1, TRAV11_TCRVA_017.1). Multiplexed cytokine analysis revealed anomalies in SCF, SCGF-b, and MCP-1 expression in this subset. CONCLUSIONS: Persistent alterations in inflammatory pathways and T-cell activation/exhaustion markers for months after active infection may help shed light on the pathophysiology of a prolonged post-viral syndrome observed following recovery from COVID-19 infection. Future studies may inform the ability to identify druggable targets involving these pathways to mitigate the long-term effects of COVID-19 infection. TRIAL REGISTRATION: https://clinicaltrials.gov/ct2/show/NCT04360278 Registered April 24, 2020.

Naturally Acquired SARS-CoV-2 Immunity Persists for Up to 11 Months Following Infection.

BACKGROUND: Characterizing the kinetics of the antibody response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is of critical importance to developing strategies that may mitigate the public health burden of coronavirus disease 2019 (COVID-19). We conducted a prospective, longitudinal analysis of COVID-19 convalescent plasma donors at multiple time points over an 11-month period to determine how circulating antibody levels change over time following natural infection. METHODS: From April 2020 to February 2021, we enrolled 228 donors. At each study visit, subjects either donated plasma or had study samples drawn only. Anti-SARS-CoV-2 donor testing was performed using the VITROS Anti-SARS-CoV-2 Total and IgG assays and an in-house fluorescence reduction neutralization assay. RESULTS: Anti-SARS-CoV-2 antibodies were identified in 97% of COVID-19 convalescent donors at initial presentation. In follow-up analyses, of 116 donors presenting at repeat time points, 91.4% had detectable IgG levels up to 11 months after symptom recovery, while 63% had detectable neutralizing titers; however, 25% of donors had neutralizing levels that dropped to an undetectable titer over time. CONCLUSIONS: Our data suggest that immunological memory is acquired in most individuals infected with SARS-CoV-2 and is sustained in a majority of patients for up to 11 months after recovery. Clinical Trials Registration. NCT04360278.

Rebound and overshoot of donor-specific antibodies to human leukocyte antigens (HLA) during desensitization with plasma exchanges in hematopoietic progenitor cell transplantation: A case report.

BACKGROUND: Donor-specific antibodies (DSA) to HLA have been associated with graft loss in hematopoietic progenitor cell (HPC) transplantation. Limited data associate therapeutic plasma exchange (TPE) with desensitization and successful engraftment. We report an attempt of desensitization and observed overshooting of DSA during transplantation. CASE REPORT AND RESULTS: A 27-year-old female with cutaneous T cell lymphoma was scheduled for HPC transplantation from her HLA-haploidentical half-sister, who carried the HLA-DRB1*13:03:01 allele. The patient had the corresponding DSA. Lacking an alternative donor option at the time, we attempted a desensitization approach by immunosuppression with tacrolimus and mycophenolate mofetil (MMF). Unexpectedly, DSA increased from a mean fluorescence intensity (MFI) of 1835 on day -63 to 9008 on day -7. The MFI increased further during 3 TPE procedures and intravenous immunoglobulin (IVIG) until day -1. After transplantation, the DSA remained elevated despite 2 more TPE/IVIG procedures and graft-versus-host disease prophylaxis with high-dose cyclophosphamide, sirolimus, and MMF. Flow cytometric crossmatch, initially negative, turned positive after transplantation. Primary graft failure occurred and was attributed to antibody-mediated rejection. A second transplantation from a 7/8 HLA-matched unrelated donor, not carrying DRB1*13:03 allele, resulted in successful engraftment. CONCLUSION: Unexpected and rapid increases of a DSA can occur despite the use of current desensitization approaches. This is problematic when conditioning has already started, as such increases are unlikely to be overcome by TPE or other interventions for desensitization. Overshoot of DSA in HPC transplantation has rarely been reported. Its cause remains unclear and can include underlying disease, immunotherapy, chemotherapy, or TPE.

A pilot trial of complement inhibition using eculizumab to overcome platelet transfusion refractoriness in human leukocyte antigen allo-immunized patients.

Heavily transfused patients frequently develop human leukocyte antigen (HLA) allo-immunization resulting in platelet transfusion refractoriness and a high risk for life-threatening thrombocytopenia. Data suggest complement activation leading to the destruction of platelets bound by HLA allo-antibodies may play a pathophysiologic role in platelet refractoriness. Here we conducted a pilot trial to investigate the use of eculizumab, a monoclonal antibody that binds and inhibits C5 complement, to treat platelet transfusion refractoriness in allo-immunized patients with severe thrombocytopenia. A single eculizumab infusion was administered to 10 eligible patients, with four (40%) patients overcoming platelet refractories assessed measuring the corrected platelet count increment (CCI) 10-60 min and 18-24 h post transfusion. Responding patients had a reduction in the requirement for subsequent platelet transfusions and had higher post-transfusion platelet increments for 14 days following eculizumab administration. Remarkably, three of the four responders met CCI criteria for response despite receiving HLA-incompatible platelets. Our results suggest that eculizumab has the ability to overcome platelet transfusion refractoriness in patients with broad HLA allo-immunization. This study establishes proof of principle that complement inhibition can treat platelet transfusion refractoriness, laying the foundation for a large multicentre trial to assess the overall efficacy of this approach (ClinicalTrials.gov, identifier: NCT02298933).

Variations in hemoglobin measurement and eligibility criteria across blood donation services are associated with differing low-hemoglobin deferral rates: a BEST Collaborative study.

BACKGROUND: Determination of blood donor hemoglobin (Hb) levels is a pre-requisite to ensure donor safety and blood product quality. We aimed to identify Hb measurement practices across blood donation services and to what extent differences associate with low-Hb deferral rates. METHODS: An online survey was performed among Biomedical Excellence for Safer Transfusion (BEST) Collaborative members, extended with published data. Multivariable negative-binomial regression models were built to estimate adjusted associations of minimum donation intervals, Hb cut-offs (high, ≥13.5 g/dL in men or ≥ 12.5 g/dL in women, vs. lower values), iron monitoring (yes/no), providing or prescribing iron supplementation (yes/no), post-versus pre-donation Hb measurement and geographical location (Asian vs. rest), with low-Hb deferral rates. RESULTS: Data were included from 38 blood services. Low-Hb deferral rates varied from 0.11% to 8.81% among men and 0.84% to 31.85% among women. Services with longer minimum donation intervals had significantly lower deferral rates among both women (rate ratio, RR 0.53, 95%CI 0.33-0.84) and men (RR 0.53, 95%CI 0.31-0.90). In women, iron supplementation was associated with lower Hb deferral rates (RR 0.47, 95%CI 0.23-0.94). Finally, being located in Asia was associated with higher low-Hb deferral rates; RR 9.10 (95%CI 3.89-21.27) for women and 6.76 (95%CI 2.45-18.68) for men. CONCLUSION: Differences in Hb measurement and eligibility criteria, particularly longer donation intervals and iron supplementation in women, are associated with variations in low-Hb deferral rates. These insights could help improve both blood donation service efficiency and donor care.

How do I structure logistic processes in preparation for outsourcing of cellular therapy manufacturing?

As cell and gene therapies (CGT) assume center stage in early-phase clinical trials for several acute and chronic diseases, there is heightened interest in the standardization and automation of manufacturing processes in preparation for commercialization. Toward this goal, a hybrid and oftentimes geographically separated model comprising regional cell procurement and infusion facilities and a centralized cell manufacturing unit is gaining traction in the field. Although CGT processing facilities in academic institutions are not involved directly in the manufacturing of these therapies, they must be prepared to collaborate with commercial or contract manufacturing organizations (CMOs) and be ready to address several supply-chain challenges that have emerged for autologous and allogeneic CGT. Academic center cell-processing facilities must handle many events up- and downstream of manufacturing such as donor screening, cell collection, product labeling, cryopreservation, transportation, and thaw infusion. These events merit closer evaluation in the context of multifacility manufacturing since standard procedures have yet to be established. Based on our institutional experience, we summarize logistical challenges encountered in the handling and distribution of CGT products in early phase studies, specifically those involving CMO (outsourced) manufacturing. We also make recommendations to standardize processes unique to the CGT supply chain, emphasizing the need to maintain needle-to-needle traceability from product collection to infusion. These guidelines will inform the development of more complex supply-chain models for larger-scale cell and gene therapeutics.

Impact of different standard red blood cell storage temperatures on human and canine RBC hemolysis and chromium survival.

BACKGROUND: Storage temperature is a critical factor for maintaining red-blood cell (RBC) viability, especially during prolonged cold storage. The target range of 1 to 6°C was established decades ago and may no longer be optimal for current blood-banking practices. STUDY DESIGN AND METHODS: Human and canine RBCs were collected under standard conditions and stored in precision-controlled refrigerators at 2°C, 4°C, or 6°C. RESULTS: During 42-day storage, human and canine RBCs showed progressive increases in supernatant non-transferrin-bound iron, cell-free hemoglobin, base deficit, and lactate levels that were overall greater at 6°C and 4°C than at 2°C. Animals transfused with 7-day-old RBCs had similar plasma cell-free hemoglobin and non-transferrin-bound iron levels at 1 to 72 hours for all three temperature conditions by chromium-51 recovery analysis. However, animals transfused with 35-day-old RBCs stored at higher temperatures developed plasma elevations in non-transferrin-bound iron and cell-free hemoglobin at 24 and 72 hours. Despite apparent impaired 35-day storage at 4°C and 6°C compared to 2°C, posttransfusion chromium-51 recovery at 24 hours was superior at higher temperatures. This finding was confounded by a preparation artifact related to an interaction between temperature and storage duration that leads to removal of fragile cells with repeated washing of the radiolabeled RBC test sample and renders the test sample unrepresentative of the stored unit. CONCLUSIONS: RBCs stored at the lower bounds of the temperature range are less metabolically active and produce less anaerobic acidosis and hemolysis, leading to a more suitable transfusion product. The higher refrigeration temperatures are not optimal during extended RBC storage and may confound chromium viability studies.

Treatment-resistant PLA2R-negative membranous nephropathy responsive to low-density lipoprotein apheresis.

Idiopathic membranous nephropathy is the most common cause of nephrotic syndrome in nondiabetic adults. The antibody most often implicated is the M-type phospholipase A2 receptor (PLA2R) antibody, found in >70% of primary membranous nephropathy cases. First-line therapy is immunosuppressive in nature, but for patients who are treatment-resistant there is a significant risk of end-stage renal disease and mortality. Hypercholesterolemia is not only a side effect of nephrotic syndrome, but also its presence may worsen renal function. A recent single-arm observational study in Japan found that low-density lipoprotein apheresis (LDL-A) was able to ameliorate nephrotic syndrome in half of patients who were resistant to medication. We present a case of treatment resistant PLA2R negative membranous nephropathy who had significant improvement following two courses of LDL-A. To our knowledge, this is the first such reported case in the United States.

An International Registry of Granulocyte Transfusions.

INTRODUCTION: Granulocyte transfusions are used to either treat or prevent life-threatening infections in neutropenic patients. Current evidence from clinical trials does not support or reject efficacy, nor guide practice. METHODS: A group of investigators have led the efforts to create an online registry to gather information on granulocyte transfusion practices from as broad a range of international settings. The data forms were adapted from an on-going study in England for electronic data management. Data is collected at the time of the request for granulocytes, weekly, at 28 days, and at 6 months. Information collected includes donor, granulocyte unit, patient and illness characteristics, and outcomes. RESULTS: The PROspective GRanulocyte usage and outcomEs Survey (ProGrES) is currently open for data entry. Centres across the UK have collected data on 80 subjects. Five institutions from 4 countries (2 from the US, 1 each from Brazil, and national services in Canada and France) are in the process of joining the study. Other countries have expressed interest. CONCLUSION: It is feasible to develop an international registry of granulocyte transfusions to characterise current practices and describe outcomes. This registry would provide a platform to explore the relationship between intervention and outcomes, and to generate evidence to inform granulocyte transfusion efficacy.

Granulocyte transfusions in the management of invasive fungal infections.

Granulocyte transfusions have a long history of being used in patients with neutropenia or neutrophil dysfunction to prevent and treat invasive fungal infections. However, there are limited and conflicting data concerning its clinical effectiveness, considerable variations in current granulocyte transfusion practices, and uncertainties about its benefit as an adjunct to modern antifungal therapy. In this review, we provide an overview on granulocyte transfusions and summarize the evidence on their role in the prevention and treatment of invasive fungal infections.

The effect of iron balance on platelet counts in blood donors.

BACKGROUND: Thrombocytosis (or, less commonly, thrombocytopenia) is associated with iron-deficiency anemia and resolves with iron therapy. Many volunteer blood donors have low iron stores, with or without anemia. Iron balance could affect platelet counts in blood donors. STUDY DESIGN AND METHODS: Whole blood donors deferred for finger-stick hemoglobin levels less than 12.5 g/dL were evaluated by complete blood count and serum iron panel before and after oral iron treatment. Group assignment for iron depletion was based on serum ferritin cutoffs of less than 20 µg/L for women and less than 30 µg/L for men or was based on changes in serum ferritin levels after iron replacement. RESULTS: Among 1273 Hb-deferred whole blood donors, 55% (619 of 1128) of the women and 70% (102 of 145) of the men were iron depleted. Iron-depleted donors had higher platelet counts compared with donors who had normal ferritin levels (women: 286 vs. 268 × 103 /µL; p < 0.0001; men: 246 vs. 222 × 103 /µL; p = 0.0454). Only 4.4% of iron-depleted donors had thrombocytosis (> 400 × 103 /µL) compared with 2.0% of donors who had normal ferritin levels (p = 0.017). Iron replacement decreased platelet counts in iron-depleted female donors (mean, -19,800/µL; interquartile range, 8000 to -45,000/µL), but not in donors who had normal or stable ferritin levels. The same trends were observed in male donors. CONCLUSION: Iron-depleted donors had higher platelet counts than donors who had adequate iron stores. Oral iron replacement decreased platelet counts on average by about 20,000/µL in iron-depleted donors but had no effect on platelet counts in donors who had normal or stable ferritin levels.

Autologous lymphapheresis for the production of chimeric antigen receptor T cells.

BACKGROUND: The first step in manufacturing chimeric antigen receptor (CAR) T cells is to collect autologous CD3+ lymphocytes by apheresis. Patients, however, often have leukopenia or have other disease-related complications. We evaluated the feasibility of collecting adequate numbers of CD3+ cells, risk factors for inadequate collections, and the rate of adverse events. STUDY DESIGN AND METHODS: Apheresis lymphocyte collections from patients participating in three CAR T-cell clinical trials were reviewed. Collections were performed on the COBE Spectra by experienced nurses, with the goal of obtaining a minimum of 0.6 × 109 and a target of 2 × 109 CD3+ cells. Preapheresis peripheral blood counts, apheresis parameters, and product cell counts were analyzed. RESULTS: Of the 71 collections, 69 (97%) achieved the minimum and 55 (77%) achieved the target. Before apheresis, the 16 patients with yields below the target had significantly lower proportions and absolute numbers of circulating lymphocytes and CD3+ lymphocytes and higher proportions of circulating blasts and NK cells than those who achieved the target (470 × 106 lymphocytes/L vs. 1340 × 106 lymphocytes/L, p = 0.008; 349 × 106 CD3+ cells/L vs. 914 × 106 CD3+ cells/L, p = 0.001; 17.6% blasts vs. 4.55% blasts, p = 0.029). Enrichment of blasts in the product compared to the peripheral blood occurred in four patients, including the two patients whose collections did not yield the minimum number of CD3+ cells. Apheresis complications occurred in 11 patients (15%) and, with one exception, were easily managed in the apheresis clinic. CONCLUSIONS: In most patients undergoing CAR T-cell therapy, leukapheresis is well tolerated, and adequate numbers of CD3+ lymphocytes are collected.

Low frequency of anti-D alloimmunization following D+ platelet transfusion: the Anti-D Alloimmunization after D-incompatible Platelet Transfusions (ADAPT) study.

The reported frequency of D alloimmunization in D- recipients after transfusion of D+ platelets varies. This study was designed to determine the frequency of D alloimmunization, previously reported to be an average of 5 ± 2%. A primary anti-D immune response was defined as the detection of anti-D ≥ 28 d following the first D+ platelet transfusion. Data were collected on 485 D- recipients of D+ platelets in 11 centres between 2010 and 2012. Their median age was 60 (range 2-100) years. Diagnoses included: haematological (203/485, 42%), oncological (64/485, 13%) and other diseases (218/485, 45%). Only 7/485 (1·44%; 95% CI 0·58-2·97%) recipients had a primary anti-D response after a median serological follow-up of 77 d (range: 28-2111). There were no statistically significant differences between the primary anti-D formers and the other patients, in terms of gender, age, receipt of immunosuppressive therapy, proportion of patients with haematological/oncological diseases, transfusion of whole blood-derived or apheresis platelets or both, and total number of transfused platelet products. This is the largest study with the longest follow-up of D alloimmunization following D+ platelet transfusion. The low frequency of D alloimmunization should be considered when deciding whether to administer Rh Immune Globulin to D- males and D- females without childbearing potential after transfusion of D+ platelets.

Initial serum ferritin predicts number of therapeutic phlebotomies to iron depletion in secondary iron overload.

BACKGROUND: Therapeutic phlebotomy is increasingly used in patients with transfusional siderosis to mitigate organ injury associated with iron overload (IO). Laboratory response variables and therapy duration are not well characterized in such patients. STUDY DESIGN AND METHODS: We retrospectively evaluated 99 consecutive patients undergoing therapeutic phlebotomy for either transfusional IO (TIO, n = 88; 76% had undergone hematopoietic transplantation) or nontransfusional indications (hyperferritinemia or erythrocytosis; n = 11). Complete blood cell count, serum ferritin (SF), transferrin saturation, and transaminases were measured serially. Phlebotomy goal was an SF level of less than 300 µg/L. RESULTS: Mean SF levels before phlebotomy among TIO and nontransfusional subjects were 3093 and 396 µg/L, respectively. Transfusion burden in the TIO group was 94 ± 108 (mean ± SD) RBC units; approximately half completed therapy with 24 ± 23 phlebotomies (range, 1-103). One-third were lost to follow-up. Overall, 15% had mild adverse effects, including headache, nausea, and dizziness, mainly during first phlebotomy. Prior transfusion burden correlated poorly with initial ferritin and total number of phlebotomies to target in the TIO group. However, number of phlebotomies to target was strongly correlated with initial SF (R(2) = 0.8; p < 0.0001) in both TIO and nontransfusional groups. ALT decreased significantly with serial phlebotomy in all groups (mean initial and final values, 61 and 39 U/L; p = 0.03). CONCLUSIONS: Initial SF but not transfusion burden predicted number of phlebotomies to target in patients with TIO. Despite good treatment tolerance, significant losses to follow-up were noted. Providing patients with an estimated phlebotomy number and follow-up duration, and thus a finite endpoint, may improve compliance. Hepatic function improved with iron offloading.

mRNA vaccine-induced antibodies more effective than natural immunity in neutralizing SARS-CoV-2 and its high affinity variants.

Several variants of SARS-CoV-2 have emerged. Those with mutations in the angiotensin-converting enzyme (ACE2) receptor binding domain (RBD) are associated with increased transmission and severity. In this study, we developed both antibody quantification and functional neutralization assays. Analyses of both COVID-19 convalescent and diagnostic cohorts strongly support the use of RBD antibody levels as an excellent surrogate to biochemical neutralization activities. Data further revealed that the samples from mRNA vaccinated individuals had a median of 17 times higher RBD antibody levels and a similar degree of increased neutralization activities against RBD-ACE2 binding than those from natural infections. Our data showed that N501Y RBD had fivefold higher ACE2 binding than the original variant. While some antisera from naturally infected subjects had substantially reduced neutralization ability against N501Y RBD, all blood samples from vaccinated individuals were highly effective in neutralizing it. Thus, our data indicates that mRNA vaccination may generate more neutralizing RBD antibodies than natural immunity. It further suggests a potential need to maintain high RBD antibody levels to control the more infectious SARS-CoV-2 variants.