AUTHOR=Sablerolles Roos S. G. , Goorhuis Abraham , GeurtsvanKessel Corine H. , de Vries Rory D. , Huckriede Anke L. W. , Koopmans Marion P. G. , Lafeber Melvin , Postma Douwe F. , van Baarle Debbie , Visser Leo G. , Dalm Virgil A. S. H. , Kootstra Neeltje A. , Rietdijk Wim J. R. , van der Kuy P. Hugo M. TITLE=Heterologous Ad26.COV2.S Prime and mRNA-Based Boost COVID-19 Vaccination Regimens: The SWITCH Trial Protocol JOURNAL=Frontiers in Immunology VOLUME=Volume 12 - 2021 YEAR=2021 URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2021.753319 DOI=10.3389/fimmu.2021.753319 ISSN=1664-3224 ABSTRACT=The present protocol study was used to summarize the findings of other major COVID-19 vaccination trials and provide an outline of our multicenter, single-blind, randomized controlled trial: the SWITCH trial. In the SWITCH, we compare the immunogenicity and reactogenicity of heterologous versus homologous vaccination strategies of COVID-19 vaccines. We recruit Health Care Workers (HCWs) who received ad.26.Cov2.S as their prime (first vaccination). We randomize HCWs in four groups: no boost (second vaccination), ad.26.Cov2.S, mRNA1273, and BNT162b2). The full protocol of the SWITCH trial can be found in the supplementary material.