Clinical Utility of SARS-CoV-2 Serological Testing and Defining a Correlate of Protection

Herein, we review established clinical use cases for SARS-CoV-2 antibody measures, which include diagnosis of recent prior infection, isolating high titer convalescent plasma, diagnosing multisystem inflammatory syndrome in children (MIS-C), and booster dosing in the immunosuppressed and other populations. We then address whether an antibody correlate of protection (CoP) for SARS-CoV-2 has been successfully defined with the following considerations: Antibody responses in the immunocompetent, vaccine type, variants, use of binding antibody tests vs. neutralization tests, and endpoint measures. In the transition from the COVID-19 pandemic to endemic, there has been much interest in defining an antibody CoP. Due to the high mutability of respiratory viruses and our current knowledge of SARS-CoV-2 variants defining a CoP for prevention of infection is unrealistic. However, a CoP may be defined for prevention of severe disease requiring hospitalization and/or death. Most SARS-CoV-2 CoP research has focused on neutralization measurements. However, there can be significant differences in neutralization test methods, and disparate responses to new variants depending on format. Furthermore, neutralization assays are often impractical for high throughput applications (e.g., assessing humoral immune response in populations or large cohorts). Nevertheless, CoP studies using neutralization measures are reviewed to determine where there is consensus. Alternatively, binding antibody tests could be used to define a CoP. Binding antibody assays tend to be highly automatable, high throughput, and therefore practical for large population applications. Again, we review studies for consensus on binding antibody responses to vaccines, focusing on standardized results. Binding antibodies directed against the S1 receptor binding domain (S1-RBD) of the viral spike protein can provide a practical, indirect measure of neutralization. Initially, a response for S1-RBD antibodies may be selected that reflects the peak response in immunocompetent populations and may serve as a target for booster dosing in the immunocompromised. From existing studies reporting peak S1-RBD responses in standardized units, an approximate range of 1372-2744 BAU/mL for mRNA and recombinant protein vaccines was extracted that could serve as an initial CoP target. This target would need to be confirmed and potentially adjusted for updated vaccines, and almost certainly for other vaccine formats (i.e., viral vector). Alternatively, a threshold or response could be defined based on outcomes over time (i.e., prevention of severe disease). We also discuss the precedent for clinical measurement of antibodies for vaccine-preventable diseases (e.g., hepatitis B). Lastly, cellular immunity is briefly addressed for its importance in the nature and durability of protection.

Evidence of premature lymphocyte aging in people with low anti-spike antibody levels after BNT162b2 vaccination

SARS-CoV-2 vaccines have unquestionably blunted the overall impact of the COVID-19 pandemic, but host factors such as age, sex, obesity, and other co-morbidities can affect vaccine efficacy. We identified individuals in a relatively healthy population of healthcare workers (CORALE study cohort) who had unexpectedly low peak anti-spike receptor binding domain (S-RBD) antibody levels after receiving the BNT162b2 vaccine. Compared to matched controls, "low responders" had fewer spike-specific antibody-producing B cells after the second and third/booster doses. Moreover, their spike-specific T cell receptor (TCR) repertoire had less depth and their CD4⁺ and CD8⁺T cell responses to spike peptide stimulation were less robust. Single cell transcriptomic evaluation of peripheral blood mononuclear cells revealed activation of aging pathways in low responder B and CD4⁺T cells that could underlie their attenuated anti-S-RBD antibody production. Premature lymphocyte aging may therefore contribute to a less effective humoral response and could reduce vaccination efficacy.

Demographic and clinical characteristics associated with variations in antibody response to BNT162b2 COVID-19 vaccination among healthcare workers at an academic medical centre: a longitudinal cohort analysis

OBJECTIVES

We sought to understand the demographic and clinical factors associated with variations in longitudinal antibody response following completion of two-dose regiment of BNT162b2 vaccination.

DESIGN

This study is a 10-month longitudinal cohort study of healthcare workers and serially measured anti-spike protein IgG (IgG-S) antibody levels using mixed linear models to examine their associations with participant characteristics.

SETTING

A large, multisite academic medical centre in Southern California, USA.

PARTICIPANTS

A total of 843 healthcare workers met inclusion criteria including completion of an initial two-dose course of BNT162b2 vaccination, complete clinical history and at least two blood samples for analysis. Patients had an average age of 45±13 years, were 70% female and 7% with prior SARS-CoV-2 infection.

RESULTS

Vaccine-induced IgG-S levels remained in the positive range for 99.6% of individuals up to 10 months after initial two-dose vaccination. Prior SARS-CoV-2 infection was the primary correlate of sustained higher postvaccination IgG-S levels (partial R2=0.133), with a 1.74±0.11 SD higher IgG-S response (p<0.001). Female sex (beta 0.27±0.06, p<0.001), younger age (0.01±0.00, p<0.001) and absence of hypertension (0.17±0.08, p=0.003) were also associated with persistently higher IgG-S responses. Notably, prior SARS-CoV-2 infection augmented the associations of sex (-0.42 for male sex, p=0.08) and modified the associations of hypertension (1.17, p=0.001), such that infection-naïve individuals with hypertension had persistently lower IgG-S levels whereas prior infected individuals with hypertension exhibited higher IgG-S levels that remained augmented over time.

CONCLUSIONS

While the IgG-S antibody response remains in the positive range for up to 10 months following initial mRNA vaccination in most adults, determinants of sustained higher antibody levels include prior SARS-CoV-2 infection, female sex, younger age and absence of hypertension. Certain determinants of the longitudinal antibody response appear significantly modified by prior infection status. These findings offer insights regarding factors that may influence the 'hybrid' immunity conferred by natural infection combined with vaccination.

Symptomology following mRNA vaccination against SARS-CoV-2

Despite demonstrated efficacy of vaccines against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of coronavirus disease-2019 (COVID-19), widespread hesitancy to vaccination persists. Improved knowledge regarding frequency, severity, and duration of vaccine-associated symptoms may help reduce hesitancy. In this prospective observational study, we studied 1032 healthcare workers who received both doses of the Pfizer-BioNTech SARS-CoV-2 mRNA vaccine and completed post-vaccine symptom surveys both after dose 1 and after dose 2. We defined appreciable post-vaccine symptoms as those of at least moderate severity and lasting at least 2 days. We found that symptoms were more frequent following the second vaccine dose than the first (74% vs. 60%, P < 0.001), with >80% of all symptoms resolving within 2 days. The most common symptom was injection site pain, followed by fatigue and malaise. Overall, 20% of participants experienced appreciable symptoms after dose 1 and 30% after dose 2. In multivariable analyses, female sex was associated with greater odds of appreciable symptoms after both dose 1 (OR, 95% CI 1.73, 1.19-2.51) and dose 2 (1.76, 1.28-2.42). Prior COVID-19 was also associated with appreciable symptoms following dose 1, while younger age and history of hypertension were associated with appreciable symptoms after dose 2. We conclude that most post-vaccine symptoms are reportedly mild and last <2 days. Appreciable post-vaccine symptoms are associated with female sex, prior COVID-19, younger age, and hypertension. This information can aid clinicians in advising patients on the safety and expected symptomatology associated with vaccination.

Antibody responses to the BNT162b2 mRNA vaccine in individuals previously infected with SARS-CoV-2

In a cohort of BNT162b2 (Pfizer–BioNTech) mRNA vaccine recipients (n = 1,090), we observed that spike-specific IgG antibody levels and ACE2 antibody binding inhibition responses elicited by a single vaccine dose in individuals with prior SARS-CoV-2 infection (n = 35) were similar to those seen after two doses of vaccine in individuals without prior infection (n = 228). Post-vaccine symptoms were more prominent for those with prior infection after the first dose, but symptomology was similar between groups after the second dose.

Virus-specific antibody levels after a single dose of the BNT162b2 vaccine in individuals previously infected with SARS-CoV-2 are similar to levels after two doses of the vaccine in infection-naive individuals.

Prior COVID-19 Infection and Antibody Response to Single Versus Double Dose mRNA SARS-CoV-2 Vaccination

The double dose regimen for mRNA vaccines against SARS-CoV-2 presents both a hope and a challenge for global efforts to curb the COVID-19 pandemic. With supply chain logistics impacting the rollout of population-scale vaccination programs, increasing attention has turned to the potential efficacy of single versus double dose vaccine administration for select individuals. To this end, we examined response to Pfizer-BioNTech mRNA vaccine in a large cohort of healthcare workers including those with versus without prior COVID-19 infection. For all participants, we quantified circulating levels of SARS-CoV-2 anti-spike (S) protein IgG at baseline prior to vaccine, after vaccine dose 1, and after vaccine dose 2. We observed that the anti-S IgG antibody response following a single vaccine dose in persons who had recovered from confirmed prior COVID-19 infection was similar to the antibody response following two doses of vaccine in persons without prior infection (P≥0.58). Patterns were similar for the post-vaccine symptoms experienced by infection recovered persons following their first dose compared to the symptoms experienced by infection naïve persons following their second dose (P=0.66). These results support the premise that a single dose of mRNA vaccine could provoke in COVID-19 recovered individuals a level of immunity that is comparable to that seen in infection naïve persons following a double dose regimen. Additional studies are needed to validate our findings, which could allow for public health programs to expand the reach of population wide vaccination efforts.

Seroprevalence of antibodies to SARS-CoV-2 in healthcare workers: a cross-sectional study

OBJECTIVE

We sought to determine the extent of SARS-CoV-2 seroprevalence and the factors associated with seroprevalence across a diverse cohort of healthcare workers.

DESIGN

Observational cohort study of healthcare workers, including SARS-CoV-2 serology testing and participant questionnaires.

SETTINGS

A multisite healthcare delivery system located in Los Angeles County.

PARTICIPANTS

A diverse and unselected population of adults (n=6062) employed in a multisite healthcare delivery system located in Los Angeles County, including individuals with direct patient contact and others with non-patient-oriented work functions.

MAIN OUTCOMES

Using Bayesian and multivariate analyses, we estimated seroprevalence and factors associated with seropositivity and antibody levels, including pre-existing demographic and clinical characteristics; potential COVID-19 illness-related exposures; and symptoms consistent with COVID-19 infection.

RESULTS

We observed a seroprevalence rate of 4.1%, with anosmia as the most prominently associated self-reported symptom (OR 11.04, p<0.001) in addition to fever (OR 2.02, p=0.002) and myalgias (OR 1.65, p=0.035). After adjusting for potential confounders, seroprevalence was also associated with Hispanic ethnicity (OR 1.98, p=0.001) and African-American race (OR 2.02, p=0.027) as well as contact with a COVID-19-diagnosed individual in the household (OR 5.73, p<0.001) or clinical work setting (OR 1.76, p=0.002). Importantly, African-American race and Hispanic ethnicity were associated with antibody positivity even after adjusting for personal COVID-19 diagnosis status, suggesting the contribution of unmeasured structural or societal factors.

CONCLUSION AND RELEVANCE

The demographic factors associated with SARS-CoV-2 seroprevalence among our healthcare workers underscore the importance of exposure sources beyond the workplace. The size and diversity of our study population, combined with robust survey and modelling techniques, provide a vibrant picture of the demographic factors, exposures and symptoms that can identify individuals with susceptibility as well as potential to mount an immune response to COVID-19.

Gene expression profile of serial samples of transformed B-cell lymphomas

Follicular lymphoma (FL) is characterized by a continuous rate of relapse and transformation to a high-grade lymphoma, usually diffuse large B-cell lymphoma (DLBCL), associated with a dismal prognosis and a poor response to conventional chemotherapy. The progression of indolent to aggressive FL is accompanied by the successive accumulation of recurrent chromosomal defects, but the resultant alterations of gene expression are largely unknown. To expand the understanding of the pathogenesis of FL transformation, we initially performed oligonucleotide microarray analyses using Affymetrix HuFL chips on five cases with matched snap-frozen lymph nodes before and after transformation. Expression data were analyzed using the Affymetrix Microarray Suite 4.0 and Genespring 4.0. Thirty-six genes with increased expression and 66 genes with decreased expression associated with transformation were identified and functionally classified. The expression of differentially expressed genes was confirmed by real-time quantitative RT-PCR (QRT-PCR) using a total of seven matched pairs and an additional five FL and five unrelated DLBCL. In addition, selected genes were further analyzed by QRT-PCR or immunohistochemistry using a large, unrelated series of FL (grades 1 to 3) as well as transformed and de novo DLBCL (total of 51 samples). The microarray results correlated with the protein expression data obtained from samples at the time of initial diagnosis and transformation. Furthermore, the expression of 25 candidate genes was evaluated by QRT-PCR with a 78% confirmation rate. Some of the identified genes, such as nucleobindin, interferon regulatory factor 4, and tissue inhibitor of metalloproteinases 1, are already known to be associated with high-grade non-Hodgkin's lymphoma. Novel candidate genes with confirmed increased and decreased expression in transformed DLBCL include ABL2 and NEK2, and PDCD1 and VDUP1, respectively. In summary, this study shows that transformation of FL to DLBCL is associated with a distinct set of differentially expressed genes of potential functional importance.

Line bisection performance of normal adults: two subgroups with opposite biases

BACKGROUND

Unilateral neglect patients may have either attentional or intentional neglect or both. Determining whether normal individuals are influenced by attentional or intentional biases will lead to a better understanding of the two types of neglect. Normal individuals may not be a homogeneous group.

OBJECTIVE

To determine whether normal individuals show attentional/sensory or intentional/premotor biases when completing line bisections.

METHODS

Thirty-two normal right-handed individuals participated. On each trial, participants were asked to move a cursor using a computer mouse to the midpoint of a line presented on a computer screen. The line could appear centered on or toward either side of the screen. Participants completed the task under two conditions: either the cursor moved in the same direction as the mouse (direct condition) or the cursor moved in the opposite direction as the mouse (indirect condition).

RESULTS

Twenty-five participants showed an attentional bias, 3 showed an intentional bias, and 4 showed no bias. Of those with an attentional bias, 13 were biased to the left, and 12 were biased to the right. Those with a right-attentional bias made larger errors when the line was presented to the left, whereas those with a left-attentional bias made larger errors when the line was presented to the right.

CONCLUSIONS

Our finding that the two attentional-biased groups produced the opposite pattern of results across the three line positions suggests the processes underlying performance in the two groups may in fact differ. Further study of these two groups may lead to a better understanding of unilateral neglect.

Response time distributions and the Stroop Task: a test of the Cohen, Dunbar, and McClelland (1990) model

Cohen, Dunbar, and McClelland's (1990) model was tested for Strooplike interference tasks by studying the shape of the distribution of response latencies produced by Ss and by the model. The model correctly anticipates changes in mean response latency (M(RT)) across congruent and incongruent conditions. It does not, however, correctly anticipate changes in the shape of the distributions, even though changes in the shape of the distributions underlie the changes in M(RT). Thus the model predicts M(RT) successfully but for the wrong reason. It is concluded that the model is not an adequate account of Ss' performance in the Stroop task.

Response time distributions and the Stroop task: A test of the Cohen, Dunbar, and McClelland (1990) model

Cohen, Dunbar, and McClelland's (1990) model was tested for Strooplike interference tasks by studying the shape of the distribution of response latencies produced by Ss and by the model. The model correctly anticipates changes in mean response latency (M(RT)) across congruent and incongruent conditions. It does not, however, correctly anticipate changes in the shape of the distributions, even though changes in the shape of the distributions underlie the changes in M(RT). Thus the model predicts M(RT) successfully but for the wrong reason. It is concluded that the model is not an adequate account of Ss' performance in the Stroop task.