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ChAdOx1 nCoV-19 Covid-19 Vaccine and the B.1.351 Variant
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This study sought to assess the efficacy of the ChAdOx1 nCoV-19 Covid-19 vaccine against the SARS-CoV-2 variant B.1.351 (501Y.V2).
- Results of the study showed that a the ChAdOx1 nCoV-19 vaccine did not offer protection against mild to moderate Covid-19 disease caused by the B.1.351 (501Y.V2) SARS-CoV-2 variant, otherwise known as the South African variant.
abstract
This abstract is available on the publisher's site.
Access this abstract nowBACKGROUND
Assessment of the safety and efficacy of vaccines against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in different populations is essential, as is investigation of the efficacy of the vaccines against emerging SARS-CoV-2 variants of concern, including the B.1.351 (501Y.V2) variant first identified in South Africa.
METHODS
We conducted a multicenter, double-blind, randomized, controlled trial 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. Participants 18 to less than 65 years of age were assigned in a 1:1 ratio 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.
RESULTS
Between June 24 and November 9, 2020, we enrolled 2026 HIV-negative adults (median age, 30 years); 1010 and 1011 participants received at least one dose of placebo or vaccine, respectively. 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% (95% confidence interval [CI], -49.9 to 59.8). 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% (95% CI, -76.8 to 54.8). The incidence of serious adverse events was balanced between the vaccine and placebo groups.
CONCLUSIONS
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.
Additional Info
Disclosure statements are available on the authors' profiles:
Efficacy of the ChAdOx1 nCoV-19 Covid-19 Vaccine Against the B.1.351 Variant
N. Engl. J. Med 2021 Mar 16;[EPub Ahead of Print], SA Madhi, V Baillie, CL Cutland, M Voysey, AL Koen, L Fairlie, SD Padayachee, K Dheda, SL Barnabas, QE Bhorat, C Briner, G Kwatra, K Ahmed, P Aley, S Bhikha, JN Bhiman, AE Bhorat, J du Plessis, A Esmail, M Groenewald, E Horne, SH Hwa, A Jose, T Lambe, M Laubscher, M Malahleha, M Masenya, M Masilela, S McKenzie, K Molapo, A Moultrie, S Oelofse, F Patel, S Pillay, S Rhead, H Rodel, L Rossouw, C Taoushanis, H Tegally, A Thombrayil, S van Eck, CK Wibmer, NM Durham, EJ Kelly, TL Villafana, S Gilbert, AJ Pollard, T de Oliveira, PL Moore, A Sigal, A IzuFrom MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
Primary Care
A Haunting Tale of Vaccines and Variants
Adding to the alphabet soup of SARS-CoV-2 and COVID-19 are the newly erupting variants that are named using the PANGO (Phylogenetic Assignment of Named Global Outbreak) lineage designation and can be assigned in a hierarchy of risk.1 The CDC provides the following classification of variants:
Primary care clinicians may recognize many of the variants of concern as they are currently circulating in the US and include B.1.1.7 (first detected in the United Kingdom), P.1 (Brazil and Japan), B.1.351 (South Africa), B.1.427 (California), and B.1.429 (California). A recent evaluation of efficacy of the ChADOx1 COVID-19 vaccine (AstraZeneca) demonstrates the potentially worrisome impact of one of these variants (B.1.351) on the COVID-19 vaccine program.2
A large, multicenter, double-blind, randomized controlled trial was conducted in South Africa between June and November 2020 and involved 750 vaccine recipients and 717 placebo recipients. Individuals received two doses, 21 to 35 days apart. During the ascertainment period, 42 individuals developed mild to moderate COVID-19, and 39 (93%) of these cases were attributed to the B.1.351 variant. Serological studies in a small subset of participants demonstrated greatly reduced live virus neutralization of the B.1.351 variant compared with the original SARS-CoV-2 strain. Not surprisingly, the vaccine showed almost no efficacy for prevention of mild to moderate COVID-19 in this trial (VE, 21.9%; 95% CI: −49.9–59.8). When limited to only B.1.351 cases, the estimated vaccine efficacy was 10.4% (−76.8–54.8).
The important lesson here is that variants matter. Mutation is a given; natural selection may favor viruses with enhanced transmissibility or the ability to escape existing immune responses. Consequently, as we ramp up vaccination, continuing our public health measures is still essential. In addition, ongoing viral surveillance and heightened vigilance are needed to provide advance warning of potential vulnerabilities in our acquired immunity and our vaccination programs.
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