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COVID-19 Vaccine AstraZeneca trials confirm 100% protection against severe disease, hospitalisation and death

Andrew Pollard, Professor of Pediatric Infection and Immunity at the University of Oxford, and chief investigator of the trials of the ChAdOx1 nCoV-19 coronavirus vaccine, volunteered his time to help deliver live-saving Covid vaccinations at the newly opened NHS Vaccine Centre at the Kassam Stadium, Oxford.
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  • Increased efficacy with longer inter-dose interval
  • Protection of over 70% starting after a first dose
  • First indication of reduction in disease transmission of up to 67%
  • AstraZeneca is also seeking Emergency Use Listing from the World Health Organization for an accelerated pathway to vaccine availability in low-income countries.
  • AstraZeneca will engage with governments, international organisations and collaborators around the world to ensure broad and equitable access to the vaccine at no profit for the duration of the pandemic.

COVID-19 Vaccine AstraZeneca is safe and effective at preventing COVID-19, with no severe cases and no hospitalisations, more than 22 days after the first dose, according to a primary analysis of the Phase III clinical trials from the UK, Brazil and South Africa.

First published as a preprint in the medical publication The Lancet the results demonstrated that the AstraZeneca vaccine had an efficacy of 76% (CI: 59% to 86%) after a first dose, with protection maintained to the second dose. With an inter-dose interval of 12 weeks or more, vaccine efficacy increased to 82% (CI: 63%, 92%).

The analysis also showed the potential for the vaccine to reduce asymptomatic transmission of the virus, based on weekly swabs obtained from volunteers in the UK trial. The data showed that PCR positive readings were reduced by 67% (CI: 49%, 78%) after a single dose, and 50% (CI: 38% to 59%) after the two-dose regimen, supporting a substantial impact on the transmission of the virus.

The primary analysis for efficacy was based on 17,177 participants accruing 332 symptomatic cases from the Phase III UK (COV002), Brazil (COV003) and South Africa (COV005) trials led by Oxford University and AstraZeneca, a further 201 cases than previously reported.

“This primary analysis reconfirms that our vaccine prevents severe disease and keeps people out of hospital,” said Sir Mene Pangalos, Executive Vice President BioPharmaceuticals R&D.

“Extending the dosing interval not only boosts the vaccine’s efficacy, but also enables more people to be vaccinated upfront. Together with the new findings on reduced transmission, we believe this vaccine will have a real impact on the pandemic,” said Pangalos.

“These new data provide an important verification of the interim data that has helped regulators such as the MHRA in the UK and elsewhere around the world to grant the vaccine emergency use authorisation. It also helps to support the policy recommendation made by the Joint Committee on Vaccination and Immunisation for a 12-week prime-boost interval, as they look for the optimal approach to roll out, and reassures us that people are protected 22 days after a single dose of the vaccine.”

Professor Andrew Pollard, Chief Investigator of the Oxford Vaccine Trial

AstraZeneca has said that data will continue to be analysed and shared with regulators around the world to support their ongoing rolling reviews for emergency supply or conditional approval during the health crisis.

One of the added benefits of the vaccine is that it can be stored, transported and handled at normal refrigerated conditions (two-eight degrees Celsius/36-46 degrees Fahrenheit) for at least six months and administered within existing healthcare settings.


COVID-19 Vaccine AstraZeneca was co-invented by the University of Oxford and its spin-out company, Vaccitech.

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