Efficacy of the ChAdOx1 nCoV-19 Covid-19 Vaccine against the B.1.351 Variant

N Engl J Med. 2021 May 20;384(20):1885-1898. doi: 10.1056/NEJMoa2102214. Epub 2021 Mar 16.

Abstract

Background: Assessment of the safety and efficacy of vaccines against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in different populations is essential, as is investigation of the efficacy of the vaccines against emerging SARS-CoV-2 variants of concern, including the B.1.351 (501Y.V2) variant first identified in South Africa.

Methods: We conducted a multicenter, double-blind, randomized, controlled trial to assess the safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) in people not infected with the human immunodeficiency virus (HIV) in South Africa. Participants 18 to less than 65 years of age were assigned in a 1:1 ratio to receive two doses of vaccine containing 5×1010 viral particles or placebo (0.9% sodium chloride solution) 21 to 35 days apart. Serum samples obtained from 25 participants after the second dose were tested by pseudovirus and live-virus neutralization assays against the original D614G virus and the B.1.351 variant. The primary end points were safety and efficacy of the vaccine against laboratory-confirmed symptomatic coronavirus 2019 illness (Covid-19) more than 14 days after the second dose.

Results: Between June 24 and November 9, 2020, we enrolled 2026 HIV-negative adults (median age, 30 years); 1010 and 1011 participants received at least one dose of placebo or vaccine, respectively. Both the pseudovirus and the live-virus neutralization assays showed greater resistance to the B.1.351 variant in serum samples obtained from vaccine recipients than in samples from placebo recipients. In the primary end-point analysis, mild-to-moderate Covid-19 developed in 23 of 717 placebo recipients (3.2%) and in 19 of 750 vaccine recipients (2.5%), for an efficacy of 21.9% (95% confidence interval [CI], -49.9 to 59.8). Among the 42 participants with Covid-19, 39 cases (95.1% of 41 with sequencing data) were caused by the B.1.351 variant; vaccine efficacy against this variant, analyzed as a secondary end point, was 10.4% (95% CI, -76.8 to 54.8). The incidence of serious adverse events was balanced between the vaccine and placebo groups.

Conclusions: A two-dose regimen of the ChAdOx1 nCoV-19 vaccine did not show protection against mild-to-moderate Covid-19 due to the B.1.351 variant. (Funded by the Bill and Melinda Gates Foundation and others; ClinicalTrials.gov number, NCT04444674; Pan African Clinical Trials Registry number, PACTR202006922165132).

Publication types

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

MeSH terms

  • Adenoviridae
  • Adolescent
  • Adult
  • Antibodies, Neutralizing / blood*
  • Antibodies, Neutralizing / physiology
  • COVID-19 / epidemiology
  • COVID-19 / immunology
  • COVID-19 / prevention & control*
  • COVID-19 Serological Testing
  • COVID-19 Vaccines / administration & dosage
  • COVID-19 Vaccines / adverse effects
  • COVID-19 Vaccines / immunology*
  • Double-Blind Method
  • Humans
  • Immunogenicity, Vaccine*
  • Middle Aged
  • SARS-CoV-2*
  • South Africa
  • T-Lymphocytes / physiology
  • Treatment Failure
  • Vaccine Potency
  • Young Adult

Substances

  • Antibodies, Neutralizing
  • COVID-19 Vaccines
  • ChAdOx1 COVID-19 vaccine

Supplementary concepts

  • SARS-CoV-2 variants

Associated data

  • ClinicalTrials.gov/NCT04444674
  • PACTR/PACTR202006922165132