Hybrid immunity expands the functional humoral footprint of both mRNA and vector-based SARS-CoV-2 vaccines

The COVID-19 pandemic catalyzed a revolution in vaccine development, leading to the testing and approval of several global vaccine platforms that have shown tremendous promise in curbing the pandemic. Yet, despite these successes, waning immunity, and the emergence of variants of concern linked to rising breakthrough infections among vaccinees, have begun to highlight opportunities to improve vaccine platforms and deployment. Real-world vaccine efficacy has highlighted the reduced risk of breakthrough infection and disease among individuals infected and vaccinated, otherwise referred to as hybrid immunity. Hybrid immunity points to the potential for more vigorous or distinct immunity primed by the infection and may confer enhanced protection from COVID-19. Beyond augmented hybrid induced neutralizing antibody and T cell immune responses, here we sought to define whether hybrid immunity may shape the functional humoral immune response to SARS-CoV-2 following Pfizer/BNT162b2 and Moderna mRNA1273 mRNA-based, and ChadOx1/AZ1222 and Ad26.COV2.S vector-based SARS-CoV-2 vaccination. Each vaccine exhibited a unique functional humoral immune profile in the setting of naïve or hybrid immunity. However, hybrid immunity showed a unique augmentation in S2-domain specific functional humoral immunity that was poorly induced in the setting of naïve immune response. These data highlight the immunodominant effect of the S1-domain in the setting of natural immunity, which is highly variable during viral evolution, and the importance of natural infection in breaking this immunodominance in driving immunity to the S2 region of the SARS-CoV-2 S2 domain that is more conserved across variants of concern. ### Competing Interest Statement G.A. is a founder and equity holder for Seromyx Systems Inc., an employee and equity holder for Leyden Labs, and has received financial support from Abbvie, BioNtech, GSK, Gilead, Merck, Moderna, Novartis, Pfizer, and Sanofi. G.A. interests were reviewed and are managed by Massachusetts General Hospital and Partners HealthCare in accordance with their conflict-of-interest policies. All other authors have declared that no conflict of interest exists. ### Funding Statement We thank Nancy Zimmerman, Mark and Lisa Schwartz, an anonymous donor (financial support), Terry and Susan Ragon, and the SAMANA Kay MGH Research Scholars award for their support. We acknowledge the support from the Ragon Institute of MGH, MIT, and Harvard (G.A) the Massachusetts Consortium on Pathogen Readiness (MassCPR) (G.A.), and the National Institutes of Health (3R37AI080289 11S1, R01AI146785, U19AI42790 01, U19AI135995 02, U19AI42790 01, 1U01CA260476 01,CIVIC75N93019C00052) (G.A.). H.Z. was funded by a UK NIHR GECO award (GEC111). ### 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: Samples from vaccinees in the UK, Latvia, and South Africa were obtained as part of a previous study of healthcare workers in pediatric facilities originally initiated at Great Ormond Street Hospital (COVID-19 Staff Testing of Antibody Responses Study (Co-STARS)), the Integrated Research Application System (IRAS) project ID: 282713, [ClinicalTrials.gov][1] Identifier: [NCT04380896][2]). Ethics approval was obtained locally by the lead investigators of each site. Ethical approvals were given by: UK: Health Research Agency in England and Health and Care Research Wales South Africa: Human Research Ethics Committee, Faculty of Health Sciences, University of Cape Town Latvia: Riga Stradinas Universitaes, Etikas Komiteja 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 and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All anonymized data collected during the trial and associated with this study can be provided. Request should be directed to d.goldblatt{at}ucl.ac.uk or alter{at}mgh.harvard.edu. Data requestors will need to sign a data access agreement to gain access, and access will be granted for non-commercial research purposes only. [1]: https://ClinicalTrials.gov [2]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT04380896&atom=%2Fmedrxiv%2Fearly%2F2022%2F07%2F04%2F2022.06.28.22276786.atom