AstraZeneca vaccine doesn't protect against South African variant of COVID-19, shows trial
South Africa: Results from a phase 1b-2 clinical trial showed two-dose regimen of the AstraZeneca-Oxford University COVID-19 vaccine to be ineffective against mild-to-moderate COVID-19 due to the B.1.351 variant.
The study, published in the New England Journal of Medicine, found that two-dose regimen of the ChAdOx1 nCoV-19 vaccine did not provide protection against mild-to-moderate infections with the B1351 variant first identified in South Africa.
Safety and efficacy assessment of vaccines against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is essential in different population, so is investigation of the efficacy of the vaccines against emerging SARS-CoV-2 variants of concern, including the B.1.351 (501Y.V2).
Shabir A. Madhi and colleagues aimed to assess the safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) in people not infected with the human immunodeficiency virus (HIV) in South Africa.
For the purpose, the researchers conducted a multicenter, double-blind, randomized, controlled trial that included participants 18 to less than 65 years of age. They were assigned in a ratio of 1:1 to receive two doses of vaccine containing 5×1010 viral particles or placebo (0.9% sodium chloride solution) 21 to 35 days apart.
Serum samples obtained from 25 participants after the second dose were tested by pseudovirus and live-virus neutralization assays against the original D614G virus and the B.1.351 variant.
The primary end points were safety and efficacy of the vaccine against laboratory-confirmed symptomatic coronavirus 2019 illness (Covid-19) more than 14 days after the second dose.
2026 HIV-negative adults were enrolled between June 24 and November 9, 2020; 1010 and 1011 participants received at least one dose of placebo or vaccine, respectively.
Key findings of the study include:
- Both the pseudovirus and the live-virus neutralization assays showed greater resistance to the B.1.351 variant in serum samples obtained from vaccine recipients than in samples from placebo recipients.
- In the primary end-point analysis, mild-to-moderate Covid-19 developed in 23 of 717 placebo recipients (3.2%) and in 19 of 750 vaccine recipients (2.5%), for an efficacy of 21.9%.
- Among the 42 participants with Covid-19, 39 cases (92.9%) were caused by the B.1.351 variant; vaccine efficacy against this variant, analyzed as a secondary end point, was 10.4%.
- The incidence of serious adverse events was balanced between the vaccine and placebo groups.
"A two-dose regimen of the ChAdOx1 nCoV-19 vaccine did not show protection against mild-to-moderate Covid-19 due to the B.1.351 variant," wrote the authors.
Reference:
The study titled, "Efficacy of the ChAdOx1 nCoV-19 Covid-19 Vaccine against the B.1.351 Variant," is published in the New England Journal of Medicine.
DOI: https://www.nejm.org/doi/full/10.1056/NEJMoa2102214
