In a phase Ib/II trial, the AstraZeneca vaccine was ineffective against both the South African SARS-CoV-2 variant or the wild-type virus.
In this South African trial, the vaccine’s overall efficacy versus mild-to-moderate COVID was 21.9% and efficacy against the B.1.351 variant was 10.4%.
Participants’ median age was 30, about 56% were men, and 71% were black. Almost 20% of participants were obese, 42% were smokers, and about 3% of those had underlying hypertension or chronic respiratory conditions. All were HIV negative. The median time between doses was 28 days.
Overall, 19 of 750 in the vaccine group (2.5%) and 23 of 717 in the placebo group (3.2%) developed mild-to-moderate COVID.
In regard to the secondary outcome of testing effectiveness against the B.1.351 variant, the authors note that “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.”
Exploratory analyses found about 33.5% efficacy against COVID of any severity more than 14 days after the first dose. No cases of severe COVID were reported among the participants, but with the groups’ demographics, especially their relatively young age, it was unlikely that severe COVID would be observed in such a small trial.
Professor Shabir Madhi, Executive Director of the Vaccines and Infectious Diseases Analytics Research Unit at Wits, said in a press release that the AstraZeneca results “threw a curveball” after the initial “euphoria” over the effectiveness of the first COVID vaccines. He nevertheless stressed that the AstraZeneca vaccine was still important in preventing hospitals being overrun with COVID patients.
Despite the disappointing results, Prof Madhi said these findings “need to be made in the context of ongoing global spread and community transmission of the B.1.351 variant”.
Source: MedPage Today
Journal information: Madhi SA, et al “Efficacy of the ChAdOx1 nCOV-19 Covid-19 vaccine against the B.1.351 variant” N Engl J Med 2021; DOI: 10.1056/NEJM2102214.
