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Efficacy of ChAdOx1 nCoV-19 Vaccine Against B.1.351 Variant
Quick Takes
- Two doses of the ChAdOx1 nCoV-19 vaccine had no efficacy against the B.1.351 variant in preventing mild-to-moderate COVID-19.
- Of note, there were no cases of hospitalization due to severe COVID-19 in either the vaccine or placebo group; hence, the trial findings cannot definitely say whether the vaccine protects against severe disease from the B.1.351 variant.
- Finally, societal decisions on the utility of the ChAdOx1 vaccine will need to be made in the context of ongoing global spread and community transmission of the B.1.351 variant and the evolution of other SARS-CoV-2 lines that may include similar mutations.
Study Questions:
What is the safety, immunogenicity, and efficacy of the ChAdOx1 nCoV-19 vaccine in preventing symptomatic coronavirus disease (COVID-19) specifically against the B.1.351 variant?
Methods:
The investigators 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 years to <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) 21-35 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 endpoints were safety and efficacy of the vaccine against laboratory-confirmed symptomatic COVID-19 illness >14 days after the second dose.
Results:
Between June 24 and November 9, 2020, 2,026 HIV-negative adults (median age, 30 years) were enrolled; 1,010 and 1,011 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 endpoint 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 (92.9%) were caused by the B.1.351 variant; vaccine efficacy against this variant, analyzed as a secondary endpoint, 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:
The authors concluded that 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.
Perspective:
This study reports that two doses of the ChAdOx1 nCoV-19 vaccine had no efficacy against the B.1.351 variant in preventing mild-to-moderate COVID-19. The lack of efficacy against the B.1.351 variant should be considered in the context of 75% efficacy in preventing mild-to-moderate COVID-19 at least 14 days after even a single dose of ChAdOx1 nCov-19 vaccine that was seen before the B.1.351 variant emerged in South Africa. Of note, there were no cases of hospitalization due to severe COVID-19 in both the vaccine and placebo group and the trial findings cannot definitely say whether the vaccine protects against severe disease from the B.1.351 variant. Finally, decisions on the utility of the ChAdOx1 nCoV-19 vaccine will need to be made in the setting of ongoing global spread and transmission of the B.1.351 variant and the evolution of other severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) lines that may include similar mutations.
Clinical Topics: Cardiovascular Care Team, COVID-19 Hub, Prevention
Keywords: Coronavirus, COVID-19, HIV, HIV Infections, Mutation, Primary Prevention, SARS-CoV-2, Sodium Chloride, Vaccines, Vaccination
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