Alliance for Pandemic Preparedness

February 13, 2021

Safety and Efficacy of the ChAdOx1 NCoV-19 (AZD1222) Covid-19 Vaccine against the B.1.351 Variant in South Africa

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[pre-print; not peer-reviewed] A randomized trial conducted in South Africa found the incidence of COVID-19 >14 days after the second dose of the AstraZeneca-Oxford SARS-CoV-2 vaccine was 93.6 per 1,000 person-years (23 cases among 717 participants) in the vaccine group and 73.1 per 1,000 person-years (19 cases among 750 participants) in the placebo group, yielding a vaccine efficacy of 22%. Of the COVID-19 cases, 39/42 (93%) were the B.1.351 variant, corresponding to a vaccine efficacy of 10% against this variant. Although the researchers conclude that the vaccine does not provide protection from mild to moderate infection caused by the B.1.351 variant, they were unable to make conclusions about protection from severe COVID-19 since no cases of severe disease or hospitalization were reported in either the vaccinated or placebo group.

Analysis of serum samples collected from 25 vaccinated participants demonstrated that the vaccine did not induce neutralization activity against the B.1.351 variant.    

Madhi et al. (2021). Safety and Efficacy of the ChAdOx1 NCoV-19 (AZD1222) Covid-19 Vaccine against the B.1.351 Variant in South Africa. Pre-print downloaded Feb 12 from https://www.medrxiv.org/content/10.1101/2021.02.10.21251247v1