[A] double-blind multicenter study, led by scientists at the South African Medical Research Council Vaccines and Infectious Diseases Analytics Research Unit, studied the safety and the efficacy of the AstraZeneca ChAdOx1 nCoV-19 vaccine in HIV-negative adults aged 18 to 64 who received either two standard doses of the vaccine or a placebo.
Of the 42 total cases of COVID-19, 39 (92.9%) were caused by B1351, for a vaccine effectiveness against this variant of 10.4% (95% CI, -76.8 to 54.8). All 42 cases were mild to moderate, and no patients were hospitalized.
“In this trial, we found 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 authors wrote. “The lack of efficacy against the B.1.351 variant should be considered in the context of the 75% efficacy (95% CI, 8.7 to 95.5) in preventing mild-to-moderate COVID-19 with onset at least 14 days after even a single dose of ChAdOx1 nCoV-19 vaccine that was observed before the B.1.351 variant emerged in South Africa.”
In early February, South African health officials paused the rollout of AstraZeneca-Oxford vaccine to investigate reports that it offered little protection against mild-to-moderate disease. It switched to using the Johnson & Johnson vaccine to immunize healthcare workers.