Inhibition of Receptor-Binding Domain - ACE2 interaction after two doses of Sinovac's CoronaVac or AstraZeneca/Oxford's AZD1222 SARS-CoV-2 vaccines

Silva, Valéria Oliveira; Yamashiro, Rosemeire; Ahagon, Cintia Mayumi; Campos, Ivana Barros de; Oliveira, Isabela Penteriche de; Oliveira, Elaine Lopes de; López-Lopes, Giselle Ibette Silva; Matsuda, Elaine Monteiro; Castejon, Marcia Jorge; Brígido, Luís Fernando de Macedo

Practical laboratory proxies that correlate to vaccine efficacy may facilitate trials, identify non-responders and inform about boosting strategies. Among clinical and laboratory markers, assays that evaluate antibodies that inhibit receptor-binding domain ligation to angiotensin-converting enzyme-2 receptor (RBI) may provide a surrogate for viral neutralization assays. We evaluated RBI before and after a median of 34 days (IQR 33-40) of the second dose of SARS-CoV-2 Sinovac's CoronaVac (CN) or AstraZeneca/Oxford's AZD1222 (AZ) vaccines in 166 individuals. Both vaccines elicited high inhibitory titers in most subjects, 95% (158/166), with signal inhibition above 30% and 89% (127/143) with more than fourfold increase from pre-vaccination titers, but titers tend to decrease over time. Both post-vaccination inhibitory titers (95%, IQR 85-97% for AZ vs 79%, IQR 60-96% for CN, p=0.004) and pre/post titer increase (AZ 76% IQR 51-86% for AZ vs 47%, IQR 24-67% for CN, p<0.0001) were higher among AstraZeneca vaccinees. Previous serological reactivity due to natural infection was associated with high pre-vaccination signal inhibition titers. The study documents robust antibody response capable of interfering with RBD-ACE2 binding. Evaluation of SARS-CoV-2 infection incidence in these populations is necessary to assess its association to protection and its duration. This article is protected by copyright. All rights reserved.