Alliance for Pandemic Preparedness

March 17, 2021

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

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  • Two doses of the Oxford-AstraZeneca (ChAdOx1 nCoV-19) vaccine did not show protection against mild-to-moderate COVID-19 among people infected with the B.1.351 variant in a multicenter randomized trial in South Africa. 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%. Among the 42 participants who developed COVID-19, 39 (92.9%) were infected with the B.1.351 variant. Vaccine efficacy against this variant, analyzed as a secondary end point, was 10.4%. The authors note that the demographic profile of enrolled participants contributed to the lack of severe COVID-19, and therefore trial results are inconclusive regarding the vaccine’s potential to protect against severe disease. [EDITORIAL NOTE: A pre-print related to this manuscript was summarized on February 12, 2020]

Madhi et al. (Mar 16, 2021). Efficacy of the ChAdOx1 NCoV-19 Covid-19 Vaccine against the B.1.351 Variant. New England Journal of Medicine. https://doi.org/10.1056/NEJMoa2102214