Vaxzevria is Highly Effective After One Dose Against Severe Disease or Hospitalisation Caused by Beta and Delta Variants of Concern




  • Real-world data from Canada showed 82% and 87% effectiveness after one dose against hospitalisation or death caused by Beta/Gamma and Delta variants respectively

23 July 2021 -- Results from the Canadian Immunization Research Network (CIRN) with support from Public Health Agency of Canada and the Canadian Institutes of Health Research, published as a pre-print, demonstrated one dose of Vaxzevria was 82% effective against hospitalisation or death caused by the Beta/Gamma variants of the SARS-CoV-2 virus. The vaccine also showed a high level of effectiveness against the Delta (B.617.2, ‘Indian’) and Alpha (B.1.1.7, ‘Kent’) variants with an 87% and 90% reduction of hospitalisations or deaths respectively.1 The effectiveness of Vaxzevria after one dose against hospitalisation or death was similar to that of other vaccines tested in the study. Follow-up time was not sufficient to report on effectiveness of Vaxzevria after two doses, other studies have shown an increased effectiveness following the indicated two dose schedule.

Vaxzevria was effective against milder symptomatic disease although, given that data was only reported after a first dose instead of the indicated two dose schedule where efficacy is known to be enhanced in this disease setting,2 the efficacy was lower than against severe disease. Vaccine effectiveness against any symptomatic disease was 50% against the Beta/Gamma variants, and 70% and 72% against the Delta and Alpha variants, respectively.

A Phase I/II trial carried out by the University of Oxford and University of the Witwatersrand in January, had shown limited efficacy against mild disease primarily due to the Beta variant. It was unable to properly ascertain vaccine efficacy against severe disease including  hospitalisation and death given that subjects were predominantly young, healthy adults who experienced mild disease only.3

Mene Pangalos, Executive Vice President, BioPharmaceuticals R&D, said: “With different variants threatening to disrupt our route out of the pandemic, this real-world evidence shows that Vaxzevria, along with other vaccines used in Canada, provides a high level of protection against the most serious forms of the disease, even after just one shot. It is essential that we continue to protect as many people as possible in all corners of the world in order to get ahead of this deadly virus.”

The analysis included 69,533 individuals who tested positive for SARS-CoV-2 during December 2020 to May 2021 in Ontario, Canada; with 28,705 (6.8%) positive for non-variants of concern SARS-CoV-2 and 40,828 (9.7%) positive for a variant of concern.

Vaxzevria, formerly AZD1222

Vaxzevria was co-invented by the University of Oxford and its spin-out company, Vaccitech. It uses a replication-deficient chimpanzee viral vector based on a weakened version of a common cold virus (adenovirus) that causes infections in chimpanzees and contains the genetic material of the SARS-CoV-2 virus spike protein. After vaccination, the surface spike protein is produced, priming the immune system to attack the SARS-CoV-2 virus if it later infects the body.

The vaccine has been granted a conditional marketing authorisation or emergency use in more than 80 countries across six continents. More than 700 million doses of COVID-19 Vaccine AstraZeneca have been supplied to 170 countries worldwide, including more than 100 countries through the COVAX Facility.


AstraZeneca (LSE/STO/Nasdaq: AZN) is a global, science-led biopharmaceutical company that focuses on the discovery, development, and commercialisation of prescription medicines in Oncology, Rare Diseases and BioPharmaceuticals, including Cardiovascular, Renal & Metabolism, and Respiratory & Immunology. Based in Cambridge, UK, AstraZeneca operates in over 100 countries and its innovative medicines are used by millions of patients worldwide. Please visit and follow the Company on Twitter @AstraZeneca.


1. Nasreen S, (2021) Effectiveness of COVID-19 vaccines against variants of concern in Ontario, Canada. MedRxiv Online:

2. Voysey, M, et al., (2021) Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK. The Lancet, 397: 99-111.

3. Madhi, SA, et al., (2021) Efficacy of the ChAdOx1 nCoV-19 Covid-19 Vaccine against the B.1.351 Variant. New England Journal of Medicine, 384: 1885-98.

Source:  AstraZeneca

Posted: July 2021

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