Efficacy of ChAdOx1 nCoV-19 (AZD1222) vaccine against SARS-CoV-2 lineages circulating in Brazil

Nat Commun. 2021 Oct 6;12(1):5861. doi: 10.1038/s41467-021-25982-w.


Several COVID-19 vaccines have shown good efficacy in clinical trials, but there remains uncertainty about the efficacy of vaccines against different variants. Here, we investigate the efficacy of ChAdOx1 nCoV-19 (AZD1222) against symptomatic COVID-19 in a post-hoc exploratory analysis of a Phase 3 randomised trial in Brazil (trial registration ISRCTN89951424). Nose and throat swabs were tested by PCR in symptomatic participants. Sequencing and genotyping of swabs were performed to determine the lineages of SARS-CoV-2 circulating during the study. Protection against any symptomatic COVID-19 caused by the Zeta (P.2) variant was assessed in 153 cases with vaccine efficacy (VE) of 69% (95% CI 55, 78). 49 cases of B.1.1.28 occurred and VE was 73% (46, 86). The Gamma (P.1) variant arose later in the trial and fewer cases (N = 18) were available for analysis. VE was 64% (-2, 87). ChAdOx1 nCoV-19 provided 95% protection (95% CI 61%, 99%) against hospitalisation due to COVID-19. In summary, we report that ChAdOx1 nCoV-19 protects against emerging variants in Brazil despite the presence of the spike protein mutation E484K.

Publication types

  • Clinical Trial, Phase III
  • Multicenter Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Brazil
  • COVID-19 / immunology*
  • COVID-19 / virology*
  • COVID-19 Vaccines / immunology*
  • ChAdOx1 nCoV-19
  • Cohort Studies
  • Dose-Response Relationship, Immunologic
  • Female
  • Hospitalization
  • Humans
  • Male
  • Middle Aged
  • Phylogeny*
  • SARS-CoV-2 / immunology*
  • Treatment Outcome
  • Vaccination
  • Viral Load / immunology
  • Young Adult


  • COVID-19 Vaccines
  • ChAdOx1 nCoV-19