Efficacy of the ChAdOx1 nCoV-19 Covid-19 Vaccine against the B.1.351 Variant
- PMID: 33725432
- PMCID: PMC7993410
- DOI: 10.1056/NEJMoa2102214
Efficacy of the ChAdOx1 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 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).
Copyright © 2021 Massachusetts Medical Society.
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Comment in
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In South Africa, a 2-dose Oxford/AZ vaccine did not prevent mild to moderate COVID-19 (cases mainly B.1.351 variant).Ann Intern Med. 2021 May;174(5):JC50. doi: 10.7326/ACPJ202105180-050. Epub 2021 May 4. Ann Intern Med. 2021. PMID: 33939483
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Interplay between Emerging SARS-CoV-2 Variants and Pandemic Control.N Engl J Med. 2021 May 20;384(20):1952-1954. doi: 10.1056/NEJMe2103931. Epub 2021 May 5. N Engl J Med. 2021. PMID: 33951359 No abstract available.
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ChAdOx1 nCoV-19 Vaccine Efficacy against the B.1.351 Variant.N Engl J Med. 2021 Aug 5;385(6):571. doi: 10.1056/NEJMc2110093. Epub 2021 Jul 21. N Engl J Med. 2021. PMID: 34289270 No abstract available.
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