ChAdOx1 nCoV-19 (AstraZeneca) vaccine is effective against the SARS-CoV-2 B.1.1.7 variant

1. The AstraZeneca vaccine was 70.4% effective against the B.1.1.7 lineage, compared to 81.5% effective against non-B.1.1.7 lineages.

2. The neutralizing titer of the vaccinated individuals was nine times lower against B.1.1.7 than the non-B.1.1.7 (Victoria) strain in vitro.

Evidence Rating Level: 1 (Excellent)

Study Rundown: As vaccines are distributed worldwide, concern is growing about the emerging variants of the COVID-19 virus. The B.1.1.7 variant has a reported higher transmission potential and is the major strain currently seen in the United Kingdom. Other studies have shown that other vaccine efficacy varies greatly depending on vaccine type and COVID-19 strain. Using data from the ongoing ChAdOx1 nCoV-19 (Oxford-AstraZeneca) vaccine efficacy trial, this study showed that the vaccine retains clinical efficacy against the B.1.1.7 strain. In this study, volunteers were randomly assigned to receive the AstraZeneca vaccine or a meningococcal control vaccine and tested for COVID-19 on a weekly basis. Positive tests were then sequenced, and viral load was estimated by Ct values from the swabs. In-vitro neutralization assays demonstrated a 9-times lower efficacy against the B.1.1.7 strain in vaccinated individuals. Despite this, clinical vaccine efficacy was calculated to be 70.4% against the B.1.1.7 versus 81.5% against the canonical Victoria lineage for symptomatic infection. Viral load was also higher for the B.1.1.7 strain compared to other variants in those vaccinated with ChAdOx1. Given these results, this points to a slightly reduced efficacy against the B.1.1.7 variant. Limitations of this study include the insufficient sample size of asymptomatic cases, leading to wide CIs and a larger difference in efficacy. Due to this, no precise conclusions can be made on clinical efficacy, but this study provides valuable information on ensuring the clinical efficacy against the new variants. This data will help inform clinical decision making regarding vaccinating the public against COVID-19.

Click to read the study in The Lancet

Click to read an accompanying editorial in The Lancet

Relevant Reading: Sensitivity of SARS-CoV-2 B.1.1.7 to mRNA vaccine-elicited antibodies

In-Depth [randomized controlled trial]: Between May 31 and Nov 13, 2020, volunteers were recruited into vaccine efficacy studies in the UK. Participants were randomly assigned to receive the ChAdOx1 n-CoV-19 (Oxford-AstraZeneca) vaccine or a meningococcal conjugate control vaccine. Swabs were taken on a weekly basis and tested by nucleic acid amplification test (NAAT). Samples positive for SARS-CoV-2 were sequenced through the COVID-19 Genomics UK consortium. Neutralizing antibody titers from participants vaccinated with ChAdOx1 were 8.9 times (95% CI 7.2-11.0) lower against B.1.1.7 compared to the Victoria (non-B.1.1.7) lineage (geometric mean ratio 8.9, 95% CI 7.2-11.0). However, the vaccine was shown to be clinically effective against the B.1.1.7 strain, but with relatively reduced efficacy compared to the original strain. For symptomatic positive infection, vaccine efficacy was 70.4% (95% CI 43.6-84.5) for B.1.1.7 and 81.5% (67.9-89.4) for Victoria lineages. Data was limited for asymptomatic cases due to insufficient sample size and unknown infection status, leading to large, overlapping confidence intervals. For determining viral load, Ct values (an inverse indicator of viral load) were taken from self-swabs. Viral load was determined to be significantly less in patients that received the ChAdOx1 vaccine than compared to the control for both strains. Patients who had been vaccinated were also positive for shorter lengths of time, determined by less consecutive positive NAAT tests compared to the control. Duration of infection did not differ between strains of the virus.

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