PT - JOURNAL ARTICLE AU - Penny L Moore AU - Thandeka Moyo-Gwete AU - Tandile Hermanus AU - Prudence Kgagudi AU - Frances Ayres AU - Zanele Makhado AU - Jerald Sadoff AU - Mathieu Le Gars AU - Griet van Roey AU - Carol Crowther AU - Nigel Garrett AU - Linda-Gail Bekker AU - Lynn Morris AU - Hanneke Schuitemaker AU - Glenda Gray TI - Neutralizing antibodies elicited by the Ad26.COV2.S COVID-19 vaccine show reduced activity against 501Y.V2 (B.1.351), despite protection against severe disease by this variant AID - 10.1101/2021.06.09.447722 DP - 2021 Jan 01 TA - bioRxiv PG - 2021.06.09.447722 4099 - http://biorxiv.org/content/early/2021/06/09/2021.06.09.447722.short 4100 - http://biorxiv.org/content/early/2021/06/09/2021.06.09.447722.full AB - The emergence of SARS-CoV-2 variants, such as 501Y.V2, with immune evasion mutations in the spike has resulted in reduced efficacy of several COVID-19 vaccines. However, the efficacy of the Ad26.COV2.S vaccine, when tested in South Africa after the emergence of 501Y.V2, was not adversely impacted. We therefore assessed the binding and neutralization capacity of n=120 South African sera (from Day 29, post-vaccination) from the Janssen phase 3 study, Ensemble. Spike binding assays using both the Wuhan-1 D614G and 501Y.V2 Spikes showed high levels of cross-reactivity. In contrast, in a subset of 27 sera, we observed significantly reduced neutralization of 501Y.V2 compared to Wuhan-1 D614G, with 22/27 (82%) of sera showing no detectable neutralization of 501Y.V2 at Day 29. These data suggest that even low levels of neutralizing antibodies may contribute to protection from moderate/severe disease. In addition, Fc effector function and T cells may play an important role in protection by this vaccine against 501Y.V2.Competing Interest StatementThe authors have declared no competing interest.