Practical laboratory proxies that correlate to vaccine efficacy may facilitate trials, identify nonresponders, and inform about boosting strategies. Among clinical and laboratory markers, assays that evaluate antibodies that inhibit receptor‐binding domain (RBD) ligation to angiotensin‐converting enzyme‐2 receptor (receptor‐binding inhibition [RBI]) may provide a surrogate for viral neutralization assays. We evaluated RBI before and aftera median of 34 days (interquartile range [IQR]: 33–40) of the second dose of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) Sinovac's CoronaVac (CN) or As-tra Zeneca/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 prevaccination titers, but titerstend 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 AZvaccinees. Previous serological reactivity due to natural infection was associated with high prevaccination signal inhibition titers. The study documents a robust antibody response capable of interfering with RBD–angiotensin‐converting enzyme binding. Evaluation of SARS‐CoV‐2 infection incidence in these populations is necessary to assess its association to protection and its duration. (AU)