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Cited by 1,257SARS-CoV-2 and COVID-19 ResearchCOVID-19 Clinical Research StudiesVaccine Coverage and Hesitancy

Efficacy of the ChAdOx1 nCoV-19 Covid-19 Vaccine against the B.1.351 Variant

Open access
Madhi, Shabir A., Baillie, Vicky, Cutland, Clare L., Voysey, Merryn, Koen, Anthonet L., Fairlie, Lee, Padayachee, Sherman D., Dheda, Keertan +43 more·2021·New England Journal of Medicine
DOI 10.1056/nejmoa2102214PMC PMC7993410

Published version of a preprint

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Abstract

BACKGROUND: 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: 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 (95.1% of 41 with sequencing data) 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. (Funded by the Bill and Melinda Gates Foundation and others; ClinicalTrials.gov number, NCT04444674; Pan African Clinical Trials Registry number, PACTR202006922165132).

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Crossref · 10.1056/nejmoa2102214

Cites

0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 14 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    Geometric mean titers fell from 297 against the original virus to 85 against the RBD-only mutant and 74 against the B.1.351 variant.

    “Geometric mean titers dropped from 297 against the original virus to 85 against the RBD-only mutant and 74 against the B.1.351 variant.”
    Quote in the paperSubstantial claim
  • Findingown data

    A total of 1467 seronegative participants, 750 assigned to vaccine and 717 to placebo, were eligible for the primary efficacy analysis.

    “A total of 1467 seronegative participants (750 assigned to the vaccine and 717 to placebo) were eligible for the primary efficacy analysis; reasons for exclusion are listed in Figure 1.”
    Quote in the paperSubstantial claim
  • Findingown data

    In a post hoc analysis using cases through October 31, 2020 as a proxy for non-B.1.351 infection, vaccine efficacy more than 14 days after a single injection was 75.4% (95% CI, 8.7 to 95.5).

    “In a post hoc analysis of vaccine efficacy at more than 14 days after a single injection through October 31, 2020, as a proxy for infection by a non–B.1.351 variant (Fig. S1),15,27 the overall attack rate of mild-to-moderate Covid-19 at least 14 days after the first injection was 1.3% in placebo recipients and 0.3% in vaccine recipients; vaccine efficacy was 75.4% (95% CI, 8.7 to 95.5) (Table S8).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [15] Tegally H, Wilkinson E, Giovanetti M, et al. Emergence and rapid spread of a new severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) lineage with multiple spike mutations in South Africa. December 22, 2020 (https://www.medrxiv.org/content/10.1101/2020.12.21.20248640v1). preprint.

      Not checked in the free run.

    • cites [27] National Institute for Communicable Diseases. Dominance of the SARS-CoV-2 501Y.V2 lineage in Gauteng. January 28, 2021 (https://www.nicd.ac.za/wp-content/uploads/2021/01/Dominance-of-the-SARS-CoV-2-501Y.V2-lineage-in-Gauteng-South-Africa-1.pdf.) preprint.

      Not checked in the free run.

  • Findingown data

    Both pseudovirus and live-virus neutralization assays showed greater resistance to the B.1.351 variant in serum samples from vaccine recipients than in samples from placebo recipients.

    “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.”
    Quote in the paperNot a substantial claim
  • Findingown data

    The live-virus assay showed lower neutralization overall than the pseudovirus assay.

    “Live-virus assay showed lower neutralization overall, relative to pseudovirus assay (Figure 2C).”
    Quote in the paperNot a substantial claim
  • May combine two claims. 17
  • Classified as probably not a substantial claim. 10

  • May combine two claims.

    Findingown data

    In the primary efficacy analysis among seronegative participants, mild-to-moderate Covid-19 occurred in 23 of 717 placebo recipients (3.2%) and 19 of 750 vaccine recipients (2.5%), giving a vaccine efficacy of 21.9% (95% CI, −49.9 to 59.8).

    “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).”
    • Also stated in: § Vaccine Efficacy · plain
      “The incidence of confirmed mild-to-moderate Covid-19 more than 14 days after the second dose among previously seronegative participants was 93.6 per 1000 person-years in the placebo group and 73.1 per 1000 person-years in the vaccine group; vaccine efficacy was 21.9% (95% CI, −49.9 to 59.8) (Table 2 and Figure 3).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    All 42 Covid-19 cases were mild (15 vaccine recipients and 17 placebo recipients) or moderate (4 vaccine recipients and 6 placebo recipients), with no severe disease or hospitalization in either group.

    “All 42 cases of Covid-19 were graded as mild (15 vaccine recipients and 17 placebo recipients) or moderate (4 vaccine recipients and 6 placebo recipients); there were no cases of severe disease or hospitalization in either group.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Between June 24 and November 9, 2020, the trial enrolled 2026 HIV-negative adults; 1010 received at least one dose of vaccine and 1011 received placebo.

    “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.”
    • Also stated in: § Participants · plain
      “We screened 3022 persons across seven sites and enrolled 2026 HIV-negative persons in the trial between June 24 and November 9, 2020.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The vaccine induced strong neutralizing antibodies at 28 days after the first dose (geometric mean titer, 132; interquartile range, 20 to 404), which rose after a second dose (geometric mean titer, 277; interquartile range, 124 to 526).

    “Humoral response to the ChAdOx1 nCoV-19 vaccine induced strong neutralizing antibodies at 28 days after the first dose (geometric mean titer, 132; interquartile range, 20 to 404), which rose further after a second dose (geometric mean titer, 277; interquartile range, 124 to 526) (Figure 2A and Table S5).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Among 12 vaccine recipients with neutralization activity against B.1.1, 7 (58%) had undetectable neutralization against B.1.351, and the remaining 5 had neutralization lower by a factor of 4.1 to 31.5.

    “Seven of the 12 participants (58%) with neutralization activity against B.1.1 had undetectable neutralization activity against the B.1.351 variant, and the remaining 5 showed neutralization that was lower by a factor of 4.1 to 31.5 (Figure 2C).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Among six placebo recipients recently infected with SARS-CoV-2, all had detectable neutralization of B.1.1; B.1.351 neutralization was undetectable in two, lower by a factor of 6.0 to 9.5 in three, and unchanged in one.

    “Among the six placebo recipients recently infected with SARS-CoV-2, all had detectable neutralization of the B.1.1 variant, whereas neutralization activity against the B.1.351 variant was undetectable in two cases, lower neutralization by a factor of 6.0 to 9.5 was noted in three cases, and no change was seen in one case (Figure 2C).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Forty-one of 42 nasal swab samples (97.6%) were successfully sequenced; 39 (95.1%) cases were caused by B.1.351 and 2 (4.9%, both in the placebo group) by B.1.1.1 and B.1.144 lineages.

    “Forty-one of the 42 nasal swab samples (97.6%) were successfully sequenced and classified; 39 (95.1%) cases were caused by the B.1.351 variant and 2 (4.9%; both in the placebo group) by the B.1.1.1 and B.1.144 lineages (Fig. S8).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Among seropositive participants, the incidence of mild-to-moderate Covid-19 more than 14 days after the second injection did not differ between placebo (81.9 per 1000 person-years) and vaccine (73.2 per 1000 person-years) recipients; vaccine efficacy was 10.6% (95% CI, −66.4 to 52.2).

    “Similarly, among seropositive participants who had had a nonreactive nucleic acid amplification test before or at randomization, the incidence of mild-to-moderate Covid-19 more than 14 days after the second injection did not differ between placebo (81.9 per 1000 person-years) and vaccine (73.2 per 1000 person-years) recipients; vaccine efficacy was 10.6% (95% CI, −66.4 to 52.2) (Table S6).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Among 13 vaccine recipients without evidence of previous SARS-CoV-2 infection, 6 (46%) had no neutralization activity against an RBD triple-mutant pseudovirus and 11 (85%) had no neutralization activity against B.1.351 pseudovirus.

    “Six of 13 vaccine recipients (46%) without evidence of previous SARS-CoV-2 infection showed no neutralization activity against an RBD triple-mutant pseudovirus (containing K417N, E484K, and N501Y variants), and 11 of the 13 (85%) had no neutralization activity against B.1.351 pseudovirus (Figure 2B).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The only serious adverse event attributed to ChAdOx1 nCoV-19 was a body temperature above 40°C after the first dose; the fever subsided within 24 hours and no reactogenicity occurred after the second dose.

    “The only serious adverse event attributed to the ChAdOx1 nCoV-19 vaccine was a body temperature above 40°C after the first dose; the fever subsided within 24 hours, and no reactogenicity was observed after the second dose.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductnone given

    Covid-19 cases were evaluated by at least two physicians who were independent of the trial and unaware of trial-group assignments.

    “Covid-19 cases were evaluated by at least two physicians who were independent of the trial and were unaware of trial-group assignments.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductown data

    The trial was a multisite, double-blind, randomized, placebo-controlled trial conducted in South Africa that assessed the safety and efficacy of two standard doses of ChAdOx1 nCoV-19 vaccine, given 21 to 35 days apart, versus saline placebo in HIV-negative adults.

    “In this multisite, double-blind, randomized, placebo-controlled trial conducted in South Africa, we assessed the safety and efficacy of two standard doses of the ChAdOx1 nCoV-19 vaccine, administered 21 to 35 days apart, as compared with saline (0.9% sodium chloride) placebo.”
    • Also stated in: § Methods · plain
      “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.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    Confidence intervals reported in the article were not adjusted for multiple comparisons.

    “Confidence intervals reported in this article have not been adjusted for multiple comparisons.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductown data

    Participants were randomly assigned in a 1:1 ratio to receive two doses of vaccine containing 5×10^10 viral particles or placebo 21 to 35 days apart.

    “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.”
    • Also stated in: § Trial Procedures · plain
      “Trial participants were randomly assigned to receive either a 0.33-to-0.5-ml dose (depending on the lot) of the ChAdOx1 nCoV-19 vaccine or placebo by intramuscular injection on the day of randomization and a second injection 21 to 35 days later.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    An independent data and safety monitoring committee reviewed efficacy and unblinded safety data.

    “An independent data and safety monitoring committee reviewed efficacy and unblinded safety data.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductown data

    The primary efficacy analysis was end-point-driven and required 42 cases to detect a vaccine efficacy of at least 60% with a lower 95% confidence bound of 0% and 80% power.

    “The primary efficacy analysis was end-point–driven for the composite of mild, moderate, or severe Covid-19 and required 42 cases to detect a vaccine efficacy of at least 60% (with a lower bound of 0% for the 95% confidence interval), with 80% power.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    Neutralizing antibody testing against the original virus and the B.1.351 variant was performed before unblinding of trial-group assignments.

    “Testing of neutralizing antibody activity against the original virus and the B.1.351 variant was undertaken before unblinding of trial-group assignments.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Interim results from South Africa for the Ad26.COV2.S vaccine reported 57% efficacy against moderate-to-severe Covid-19 and 89% against severe Covid-19 mainly due to B.1.351.

    “Interim results from South Africa reported a vaccine efficacy of 57% against moderate-to-severe Covid-19 and 89% against severe Covid-19 mainly due to the B.1.351 variant.13”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [13] Johnson & Johnson. Johnson & Johnson COVID-19 vaccine authorized by U.S. FDA for emergency use — first single-shot vaccine in fight against global pandemic. February 27, 2021 (https://www.jnj.com/johnson-johnson-announces-single-shot-janssen-covid-19-vaccine-candidate-met-primary-endpoints-in-interim-analysis-of-its-phase-3-ensemble-trial).

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    The trial was monitored by an external clinical research organization that ensured adherence to the protocol.

    “The trial was monitored by an external clinical research organization, which ensured adherence to the protocol.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Study design and conductown data

    Vaccine efficacy against B.1.351 was estimated in a secondary analysis, while the trial was powered for the primary objective of at least 60% efficacy against Covid-19 of any severity irrespective of variants.

    “Of note, the vaccine efficacy in preventing Covid-19 due to the B.1.351 variant was estimated in a secondary analysis; the trial was powered for the primary objective of a vaccine efficacy of at least 60% in preventing Covid-19 of any severity, irrespective of variants.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Neutralizing activity of mRNA vaccines against B.1.351 was lower by a factor of 8.6 for mRNA-1273 and 6.5 for BNT-162b2 than against D614G, with no difference against B.1.1.7-like mutant.

    “Neutralizing activity of the two mRNA vaccines against the B.1.351 variant has also been observed to be lower, by a factor of 8.6 (mRNA-1273 vaccine [Moderna]) or 6.5 (BNT-162b2 vaccine [Pfizer]) on pseudovirus neutralization assay, than activity against the D614G virus, whereas no difference was evident against the N510Y.V1 (B.1.1.7)–like mutant.19,28,29”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [19] Wang P, Liu L, Iketani S, et al. Increased resistance of SARS-CoV-2 variants B.1.351 and B.1.1.7 to antibody neutralization. January 26, 2021 (https://www.biorxiv.org/content/10.1101/2021.01.25.428137v1). preprint. source

      Not checked in the free run.

    • cites [28] Muik A, Wallisch A-K, Sänger B, et al. Neutralization of SARS-CoV-2 lineage B.1.1.7 pseudovirus by BNT162b2 vaccine-elicited human sera. Science 2021 January 29 (Epub ahead of print). 33514629 PMC7971771 source

      Not checked in the free run.

    • cites [29] Liu Y, Liu J, Xia H, et al. Neutralizing activity of BNT162b2-elicited serum. N Engl J Med. DOI: 10.1056/NEJMc2102017. PMC7944950 33684280 source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    In convalescent donors infected with prototype lineage virus, 48% of serum samples could not neutralize B.1.351, and the rest showed reduced neutralization titers by a factor of 3 to 86.

    “The sensitivity of B.1.351 to neutralizing antibodies from convalescent donors infected with the prototype lineage virus, assessed with a spike-pseudovirus neutralization assay, indicated that 48% of serum samples were unable to neutralize B.1.351, with the rest showing a reduction in neutralization titers by a factor of 3 to 86.21”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [21] Wibmer CK, Ayres F, Hermanus T, et al. SARS-CoV-2 501Y.V2 escapes neutralization by South African COVID-19 donor plasma. Nat Med 2021 March 2 (Epub ahead of print). 33654292 source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductnone given

    Injections were prepared and administered by site staff aware of trial-group assignments but not involved in other trial procedures, while participants and all other trial staff remained unaware of assignments.

    “Injections were prepared and administered by site staff who were aware of participants’ trial-group assignments but were not involved in any other trial procedures. Trial participants and all other trial staff remain unaware of trial-group assignments.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductnone given

    Vaccine efficacy against the B.1.351 variant was a prespecified secondary objective.

    “Vaccine efficacy against the B.1.351 variant was a prespecified secondary objective.”
    Quote in the paperSubstantial claim
24 of 24

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • These variants are partially resistant to neutralization by monoclonal antibodies against spike, convalescent plasma, and sera from vaccinated participants.

    “recent reports suggest that these variants are partially resistant to neutralization by monoclonal antibodies against spike protein, by convalescent plasma and, notably, by sera from participants who have received severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines91,94,95.”

    From Prospects for durable immune control of SARS-CoV-2 and prevention of reinfection (2021) · cites this paper as [95]

  • If protection fails when antibody neutralization is lost even though T cell recognition persists, this points to a primary role for neutralizing antibodies.

    “Alternatively, if the loss of antibody neutralization abrogates protection even when T cell recognition is maintained, this suggests a primary role for neutralizing antibodies95.”

    From Prospects for durable immune control of SARS-CoV-2 and prevention of reinfection (2021) · cites this paper as [95]

  • Recent studies have consistently reported lower neutralizing antibody titers against B.1.351 after vaccination but not against B.1.1.7.

    “Concerning neutralization of VOCs, recent studies have consistently reported lower neutralizing antibody titers against B.1.351 after vaccination but not against B.1.1.7 (39, 42, 48–59).”

    From SARS-CoV-2 variants of concern partially escape humoral but not T cell responses in COVID-19 convalescent donors and vaccine recipients (2021) · cites this paper as [39]

  • Several studies have shown reduced vaccine efficacy against mild to moderate COVID-19 in countries where B.1.351 was dominant, although protection against severe disease appears preserved.

    “Several studies have now shown that there is reduced vaccine efficacy against mild to moderate disease in countries where B1.351 was dominant (Zhou et al., 2021; Shinde et al., 2021; Madhi et al., 2021, Vaccines and Related Biological Products Advisory Committee, 2021), although protection against severe disease appears to be preserved.”

    From Reduced neutralization of SARS-CoV-2 B.1.617 by vaccine and convalescent serum (2021) · cites this paper as Madhi et al., 2021

  • In a phase 2 trial in South Africa (N=2026), ChAdOx1-nCoV19 reported vaccine efficacy of 22% (95% CI, −50 to 60) overall, and 10% (95% CI, −77 to 55) against the B.1.351 variant, with the latter comprising 95% of cases.

    “ChAdOx1-nCoV19 was evaluated in a phase 2 trial (N=2026) in South Africa, in a study population resembling ours with predominantly mild to moderate Covid-19, and reported vaccine efficacy of 22% (95% CI: −50 to 60) overall, and 10% (95% CI: −77 to 55) against the B.1.351 variant, with the latter comprising 95% of cases.25”

    From Efficacy of NVX-CoV2373 Covid-19 Vaccine against the B.1.351 Variant (2021) · cites this paper as [25]

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Vaccine and placebo recipient counts are reversed

    Minor

    The abstract assigns 1010 recipients to placebo and 1011 to vaccine, while the Results section assigns 1010 to vaccine and 1011 to placebo.

1 of 1

Cites

Flagged first, then by citations

Research works printed but not linked: 5

  1. Pfizer. Pfizer and BioNTech announce vaccine candidate against COVID-19 achieved success in first interim analysis from phase 3 study. November 9 2020 (https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-announce-vaccine-candidate-against).
  2. Tegally H Wilkinson E Giovanetti M et al. Emergence and rapid spread of a new severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) lineage with multiple spike mutations in South Africa. December 22 2020 (https://www.medrxiv.org/content/10.1101/2020.12.21.20248640v1). preprint. · DOI
  3. Emary KRW Golubchik T Aley PK et al. Efficacy of ChAdOx1 nCoV-19 (AZD1222) vaccine against SARS-CoV-2 VOC 202012/01 (B.1.1.7). February 4 2021. preprint.
  4. National Institute for Communicable Diseases. Dominance of the SARS-CoV-2 501Y.V2 lineage in Gauteng. January 28 2021 (https://www.nicd.ac.za/wp-content/uploads/2021/01/Dominance-of-the-SARS-CoV-2-501Y.V2-lineage-in-Gauteng-South-Africa-1.pdf.) preprint.
  5. Amnesty International. COVID-19: Oxford/AstraZeneca vaccine a boost for global access but huge inequality remains. November 23 2020 (https://www.amnesty.org/en/latest/news/2020/11/oxford-astrazeneca-vaccine-a-boost-for-global-access-but-huge-inequality-remains).

Cited by

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Authors
Madhi, S. A., Baillie, V., Cutland, C. L., Voysey, M., Koen, A. L., Fairlie, L., Padayachee, S. D., Dheda, K., Barnabas, S. L., Bhorat, Q. E., Briner, C., Kwatra, G., Ahmed, K., Aley, P., Bhikha, S., Bhiman, J. N., Bhorat, A. E., du Plessis, J., Esmail, A., Groenewald, M., Horne, E., Hwa, S.-H., 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, C. K., Durham, N. M., Kelly, E. J., Villafana, T. L., Gilbert, S., Pollard, A. J., de Oliveira, T., Moore, P. L., Sigal, A., & Izu, A.
Affiliations
  • South African Medical Research Council (ZA)
  • University of the Witwatersrand (ZA)
  • University of Oxford (GB)
  • Setshaba Research Centre (ZA)
  • University of Cape Town (ZA)
  • Stellenbosch University (ZA)
  • Soweto CTC (ZA)
  • National Health Laboratory Service (ZA)
  • From the South African Medical Research Council Vaccines and Infectious Diseases Analytics Research Unit (S.A.M., V.B., A.L.K., G.K., S.B., J.P., A.J., M.L., S.M., A.M., C.T., A.T., A.I.), African Leadership in Vaccinology Expertise (C.L.C.), Wits Reproductive Health and HIV Institute (L.F., E.H., M. Masenya, F.P., S.E.), the Antibody Immunity Research Unit, School of Pathology (J.N.B., C.K.W., P.L.M.), and the Perinatal HIV Research Unit (C.B.), Faculty of Health Sciences, and the Department of Science and Innovation/National Research Foundation South African Research Chair Initiative in Vaccine Preventable Diseases Unit (S.A.M., V.B., A.L.K., G.K., S.B., A.I.), University of the Witwatersrand, and the National Institute for Communicable Diseases (NICD) of the National Health Laboratory Service (NHLS) (J.N.B., C.K.W., P.L.M.), Johannesburg, Setshaba Research Centre, Tshwane (S.D.P., K.A., M. Malahleha, M. Masilela, K.M.), the Division of Pulmonology, Groote Schuur Hospital and the University of Cape Town ...
  • Africa Health Research Institute (ZA)
  • Max Planck Institute for Infection Biology (DE)
  • AstraZeneca (United Kingdom) (GB)
Corresponding author
Madhi, Shabir A.
ORCID
Venue
New England Journal of Medicine
Publisher
Massachusetts Medical Society
Published
2021-05-20
Volume
384
Issue
20
Pages
1885-1898
ISSN
  • 0028-4793 (ISSN-L)
  • 1533-4406
DOI
10.1056/nejmoa2102214
PMC
PMC7993410
OpenAlex
W3139533040
Cited by
1,257
References
23
Citations by year
2026: 9 · 2025: 33 · 2024: 64 · 2023: 135 · 2022: 413 · 2021: 600 · 2020: 2
FWCI
96.76
Type
journal article
Language
en
Open access
Licence
Locations
  • New England Journal of Medicine (publishedVersion, cc-by)
  • medRxiv (acceptedVersion, cc-by-nc-nd)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
  • LSHTM Research Online (London School of Hygiene and Tropical Medicine) (acceptedVersion)
Funders
  • Bill and Melinda Gates Foundation (INV-017710)
  • South African Medical Research Council (96167)
  • U.K. Research and Innovation (MC_PC_19055)
  • UK National Institute for Health Research
Topics
  • Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
  • Health Sciences › Medicine › Infectious Diseases › COVID-19 Clinical Research Studies
  • Social Sciences › Health › Vaccine Coverage and Hesitancy
Keywords
ChAdOx1 nCoV-19 vaccine, COVID-19 vaccine efficacy, B.1.351 variant, SARS-CoV-2 variants of concern, neutralizing antibodies, pseudovirus neutralization, symptomatic COVID-19, vaccine safety, adenovirus vector vaccine
MeSH terms
Immunogenicity, Vaccine, COVID-19, SARS-CoV-2, COVID-19 Vaccines, COVID-19 Serological Testing, ChAdOx1 nCoV-19, Adenoviridae, Adolescent, Adult, Double-Blind Method, Humans, Middle Aged, South Africa, T-Lymphocytes, Treatment Failure, Young Adult, Antibodies, Neutralizing, Vaccine Potency

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-06.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-06.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

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