Immune and behavioral correlates of protection against symptomatic post-vaccination SARS-CoV-2 infection

Background We sought to determine immune and behavioral pre-infection correlates of protection against SARS-CoV-2 post-vaccine infections in a joint analysis of epidemiological and immunological cohort data. Methods Serum and saliva samples from 176 BNT162b2-vaccinated adults in the Prospective Assessment of SARS-CoV-2 Seroconversion study were collected between October and December 2021 and assessed for serum and saliva levels of Wuhan-1 wild-type (WT) SARS-CoV-2 Spike (S)-specific IgG and IgA binding antibodies (bAb) using a multiplex microsphere-based immunoassay (MMIA). Serum samples were also assessed for WT receptor binding domain (RBD)-specific bAb by two commercial assays, BA.1 S-specific IgG bAb by MMIA, and neutralization activity against D614G, Delta (B.1.617.2), and Omicron BA.1 and BA.1.1 variants using a lentiviral pseudovirus neutralization assay. After the Fall 2021 visit, participants reported all positive PCR and/or antigen tests for SARS-CoV-2. Duration, severity, and type of symptoms, as well as risk exposures and adherence to precautionary measures, were assessed by questionnaires during the Spring 2022 visit. Results Thirty-two participants (18.2%) developed symptomatic post-vaccination SARS-CoV-2 infections (PVI) between December 7, 2021 and April 1, 2022. Pre-infection WT (geometric mean (GM) of 3,863 vs 2,736 binding antibody unit [BAU]/ml, uninfected vs PVI, p=0.0098) and BA.1 (GM of 276.9 vs 179.9 arbitrary bAb unit [AU]/ml, uninfected vs PVI, p=0.04) anti-S IgG bAb levels measured by MMIA and neutralizing titers (NT) against BA.1 (GM titer [GMT] of 493.6 vs 286.2, uninfected vs PVI, p=0.0313) and BA.1.1 (GMT of 552.0 vs 302.5, uninfected vs PVI, p=0.021) were significantly higher in individuals that did not develop PVIs. WT anti-S bAb levels greater than 5,000 BAU/ml were associated with > 90% protection against symptomatic PVI. In individuals that developed PVI, WT anti-S IgG bAb levels correlated with lower disease severity scores (ρ= −0.3859, p=0.032) and shorter duration of clinical disease (ρ= −0.5273, p=0.0023). WT anti-RBD bAb levels measured by commercial assays correlated strongly with bAb levels measured by MMIA (ρ=0.8239, p<0.0001 and ρ=0.6929, p<0.0001, Roche and Siemens assays, respectively), but did not reach statistical significance for correlation with protection against PVI. Home risk score, but neither work nor home precautionary measures, correlated strongly with risk of PVI (mean score of 20.77 vs 47.33, uninfected vs PVI respectively, p<0.0001). Conclusions Anti-S IgG bAb levels (directed against either WT or Omicron BA.1 subvariant) and NTs served as correlates of protection against symptomatic SARS-CoV-2 infection. Anti-S (WT) IgG bAb levels remained a significant correlate of protection against PVIs when adjusting for demography and risk behavior. Results of this study also suggest that commercial assays for anti-S bAb may need to be reformatted to enable detection of higher maximum values for use as predictors of increased susceptibility to SARS-CoV-2 infection. ### Competing Interest Statement S.D.P., T.H.B, and D.R.T. report that the USU IDCRP, a U.S. Department of Defense (DoD) Institution, and the HJF were funded under a Cooperative Research and Development Agreement to conduct an unrelated phase III COVID-19 monoclonal antibody immunoprophylaxis trial sponsored by AstraZeneca. The HJF, in support of the USU IDCRP, was funded by the DoD Joint Program Executive Office for Chemical, Biological, Radiological, and Nuclear Defense to augment the conduct of an unrelated phase III vaccine trial sponsored by AstraZeneca. Both trials were part of the USG COVID-19 response. Neither is related to the work presented here. ### Funding Statement The protocol was executed by the Infectious Disease Clinical Research Program (IDCRP), a Department of Defense (DoD) program executed by the Uniformed Services University of the Health Sciences (USUHS) through a cooperative agreement by the Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc. (HJF). This work was supported in whole, or in part, with federal funds from the Defense Health Program (HU00012020067, HU00012120094) and the Immunization Healthcare Branch (HU00012120104) of the Defense Health Agency, United States Department of Defense, from the National Institute of Allergy and Infectious Disease (HU00011920111) under Inter-Agency Agreement Y1-AI-5072, from the Armed Forces Health Surveillance Division (AFHSD), Global Emerging Infections Surveillance (GEIS) Branch, under award ProMIS ID P0099\_22\_NM and Navy WUN A1417, and from the US Food and Drug Administration Medical Countermeasures Initiative grant # OCET 2022-1750. The sponsors had no involvement in the study design, the collection of data, the analysis of data, the interpretation of data, the writing of the report, or in the decision to submit the article for publication. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study protocol was approved by the Uniformed Services University of the Health Sciences' Institutional Review Board in compliance with all applicable federal regulations governing the protection of human subjects. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data for this study are available from the Infectious Disease Clinical Research Program (IDCRP), headquartered at the Uniformed Services University of the Health Sciences (USU), Department of Preventive Medicine and Biostatistics. Review by the USU Institutional Review Board is required for use of the data collected under this protocol. Furthermore, the data set includes Military Health System data collected under a Data Use Agreement that requires accounting for uses of the data. Data requests may be sent to: Address: 6270A Rockledge Drive, Suite 250, Bethesda, MD 20817. Email: contactus{at}idcrp.org. * AU : arbitrary unit bAb : binding antibody BAU : binding antibody unit CCI : Charlson comorbidity index MMIA : multiplex microsphere-based immunoassay PVI : post-vaccination infection