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

ABSTRACT

BACKGROUND: Assessment of the safety and efficacy of vaccines against the severe acute respiradetory 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 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 ChAdOxl 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 11 ratio to receive two doses of vaccine containing 5x1O10 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 D6146 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 Covid49 developed in 23 of 717 placebo recipients (3.296) and in 19 of750 vaccine recipients (2.596), for an efficacy of 21.9% (95% confidence interval ICI], -49.9 to 59.8). Among the 42 participants with Covid49, 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 ChAdOxl nCoV-19 vaccine did not show protection against mild-to-moderate Covid49 due to the B.1.351 variant. [ABSTRACT FROM AUTHOR] Copyright of New England Journal of Medicine is the property of New England Journal of Medicine and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)