AstraZeneca COVID-19 vaccine data hint at single-dose efficacy, effect on asymptomatic cases

Full data from late-phase trials of AstraZeneca’s COVID-19 vaccine have pointed to the potential for AZD1222 to work after a single dose and prevent asymptomatic cases but left key questions about the efficacy of the candidate unanswered.

The results, which were posted in The Lancet, reiterate the headline findings shared by AstraZeneca and its partners at the University of Oxford. In a pooled analysis of 11,636 participants enrolled in two separate clinical trials in the U.K. and Brazil, the efficacy of two doses of the vaccine was 70%. The paper adds the detail that protection against symptomatic disease after at least one standard dose was 64%.