This evidence synthesis has been compiled by members of the CITF Secretariat and does not necessarily represent the views of all CITF members.

By Mercedes Yanes Lane

A randomized control trial in South Africa, the results of which have been published in the New England Journal of Medicine, has found that the Oxford-AstraZeneca vaccine, although safe, is not effective against the B.1.351 variant, also known as the South African variant.

This study reports on a phase 1b-2, randomized, double-blind, placebo-controlled trial evaluating the ChAdOx1 nCoV-19 vaccine (also known as the Oxford-AstraZeneca vaccine) in South Africa. The capacity of vaccine-induced antibodies to eliminate the B.1.351 variant was tested with two different assays (pseudo virus and live virus neutralization assays). These tests showed that people who had no antibodies before vaccination did not develop antibodies capable of eliminating this variant, when measured 14 days after the second ChAdOx1 nCoV-19 vaccine dose.


The authors assessed the safety and efficacy of two standard doses of the ChAdOx1 nCoV-19 vaccine, administered 21 to 35 days apart, compared to placebo, in adults 18 to 65 years old. The safety component of the study assessed adverse physical reactions to vaccination within seven days of an injection, as well as adverse events within 28 days of an injection. The primary efficacy component evaluated the development of symptomatic SARS-CoV-2 infection in both vaccinated and unvaccinated participants. Researchers also invited a group of participants who 1) did not have antibodies against SARS-CoV-2 before vaccination, and 2) who developed antibodies against the D614G virus (the prevalent variant up to now) post-vaccination, to undergo further testing with neutralization assays 14 days after the second dose. As a secondary goal, researchers aimed to determine the capacity of vaccine-induced antibodies to eliminate the B.1.351 variant.

In total, 1467 participants did not have antibodies at baseline and were eligible for the analysis. There were no identified differences in adverse events between vaccinated and placebo groups. When looking at the primary efficacy endpoint, researchers found that 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% (95% confidence interval (CI), −49.9 to 59.8).

Twenty-five participants were eligible for neutralization capacity testing against the B.1.351 variant. Of these, six were in the placebo group, and six from the vaccine group had evidence of a post-immunization SARS-CoV-2 infection, thus 13 participants were included for neutralization tests. Among these 13 participants, 11 (85%) developed antibodies that could not eliminate the B.1.351 variant when tested on the pseudo virus neutralization assay. With the live virus assay, even fewer participants showed the capacity to eliminate the variant. Overall, efficacy of the vaccine against B.1.351 was not evident (10.4%; 95% CI, −76.8 to 54.8).

The authors conclude that this is a call for action to maximize vaccination efforts and to assemble a united front in achieving worldwide vaccine coverage.


Madhi SA, Baillie V, Cutland CL, Voysey M, Koen AL, Fairlie L, Padayachee SD, Dheda K, Barnabas SL, Bhorat QE, Briner C, Kwatra G, Ahmed K, Aley P, Bhikha S, Bhiman JN, Bhorat AE, du Plessis J, Esmail A, Groenewald M, Horne E, Hwa SH, Jose A, Lambe T, Laubscher M, Malahleha M, Masenya M, Masilela M, McKenzie S, Molapo K, Moultrie A, Oelofse S, Patel F, Pillay S, Rhead S, Rodel H, Rossouw L, Taoushanis C, Tegally H, Thombrayil A, van Eck S, Wibmer CK, Durham NM, Kelly EJ, Villafana TL, Gilbert S, Pollard AJ, de Oliveira T, Moore PL, Sigal A, Izu A; NGS-SA Group Wits–VIDA COVID Group. Efficacy of the ChAdOx1 nCoV-19 Covid-19 vaccine against the B.1.351 variant. N Engl J Med. 2021 Mar 16. doi: 10.1056/NEJMoa2102214