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AstraZeneca's COVID-19 vaccine was not protective against mild-to-moderate disease from either the so-called South African variant (B.1.351) or the wild type virus, an interim analysis of phase Ib/II data found.

Overall vaccine efficacy against mild-to-moderate COVID-19 in South Africa was 21.9% (95% CI -49.9 to 59.8), and efficacy against B.1.351 was 10.4% (95% CI -76.8 to 54.8), reported Shabir Madhi, PhD, of University of the Witwatersrand in Gauteng, South Africa, and colleagues, in the

Previously, pooled efficacy data on the AstraZeneca vaccine from the U.K., Brazil, and South Africa, prior to B.1.351's emergence, showed overall efficacy of 66.7% (95.8% CI 57.4-74.0), as well as 74.6% efficacy against the so-called U.K. variant, B.1.1.7.

From June 24 to Nov. 9, 2,026 HIV-negative adults, ages 18-65, in South Africa were randomized to receive two standard doses of vaccine or placebo administered 21-35 days apart. Primary endpoint was safety and efficacy against laboratory-confirmed COVID-19 more than 14 days after the second dose, while a secondary endpoint examined vaccine efficacy against the B.1.351 variant.

Participants' median age was 30, about 56% were men, and 71% were Black Africans. Almost 20% of participants had obesity, 42% were smokers, and about 3% apiece had underlying hypertension or chronic respiratory conditions. Median time between doses was 28 days.

Overall, 23 of 717 in the placebo group (3.2%) and 19 of 750 in the vaccine group (2.5%) developed mild-to-moderate disease. Adults with COVID-19 received a nasal swab, and 41 of 42 were sequenced, revealing 39 cases were from the B.1.351 variant.

Regarding the secondary outcome of protecting against COVID-19 disease from the B.1.351 variant, the authors noted, "the trial was powered for the primary objective of a vaccine efficacy of at least 60% in preventing COVID-19 of any severity, regardless of variants."

Madhi's group also noted there were no cases of hospitalization due to severe COVID-19 in either group, but because of participants' demographic and clinical profile, "the trial findings are inconclusive" with regards to whether or not the vaccine protects against severe disease from the B.1.351 variant.

Exploratory analyses found about 33.5% efficacy (95% CI -13.4 to 61.7) against COVID-19 of any severity more than 14 days after the first dose.

Despite these results, the authors said deliberations on the utility of this vaccine "need to be made in the context of ongoing global spread and community transmission of the B.1.351 variant" and other strains with similar mutations.

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