ChAdOx1 nCov-19 AstraZeneca COVID-19 vaccine not effective against B.1.351 variant

1. The ChAdOx1 nCov-19 (AstraZeneca) vaccine was not effective for the prevention of mild-to-moderate COVID-19 infection caused by the B.1.351 variant. 

2. The ChAdOx1 nCov-19 vaccine was effective against mild-to-moderate non-variant COVID-19 infection after a single injection.

Evidence Rating Level: 1 (Excellent)     

Study Rundown: With the emergence of COVID-19 variants, there is the need to investigate vaccine efficacy in this new context. In a randomized controlled trial from South Africa, researchers compared symptomatic COVID-19 infection rates after administration of the ChAdOx1 nCov-19 vaccine, manufactured by AstraZeneca. The study determined two doses of the vaccine were not effective at preventing mild-to-moderate COVID-19 infection caused by the B.1.351 variant. While no evidence was available for the vaccine’s efficacy against severe B.1.351 infection, this study suggests that second-generation COVID-19 vaccines may be needed to protect against this new variant. This study provides strong justification for using the ChAdOx1 nCov-19 vaccine in populations without the new B.1.351 variant. A major limitation of this study is its inability to establish the efficacy of the vaccine against severe covid-19 infection caused by the B.1.351 variant. Nonetheless, the findings were significant, as the study found that the vaccine is effective against non-variant covid-19 infection.

Click to read the study in the NEJM

Relevant Reading: Safety and efficacy of the ChAdOx1 nCov-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomized controlled trials in Brazil, South Africa, and the UK.

In-Depth [randomized controlled trial]: This multicenter, double-blind, randomized controlled trial enrolled 2,026 patients between June 24 and November 9, 2020. Adults between the ages of 18 and 65 with no or well-managed prior comorbidities were eligible for participation in the trial. Patients with human immunodeficiency virus (HIV), previous COVID-19 infection, a history of anaphylaxis after vaccination, and obesity were excluded from the study. Patients were randomized in 1:1 ratio to receive either the ChAdOx1 nCovid-19 vaccine or placebo, respectively. The primary endpoint was symptomatic COVID-19 infection after two weeks following the second injection confirmed by PCR testing. The study also aimed to investigate the efficacy of the vaccine against the new B.1.351 variant. There were 42 cases of mild and moderate COVID-19 infection confirmed, of which 39 cases were caused by the B.1.351 variant. Vaccine recipients accounted for 19 (2.5%) of these infections, while placebo recipients made up the remaining 23 (3.2%) cases. The study revealed a 75.4% vaccine efficacy (95% confidence interval [CI], 8.7 to 95.5) for the prevention of mild-to-moderate COVID-19 infection caused by non-B.1.351 variant two weeks after just a single injection. However, vaccine efficacy against the B.1.351 variant was determined to be 10.4% (95% CI, -76.8 to 54.8). The study concluded that the ChAdOx1 nCovid-19 vaccine does not protect against mild-to-moderate COVID-19 infection caused by the B.1.351 variant. No conclusion was possible on vaccine prevention of severe COVID-19 infection caused by the B.1.351 variant.

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