Cookies on this website
We use cookies to ensure that we give you the best experience on our website. If you click 'Continue' we'll assume that you are happy to receive all cookies and you won't see this message again. Click 'Find out more' for information on how to change your cookie settings.

Oxford-AstraZeneca coronavirus vaccine 79% effective against symptomatic COVID-19 overall. Vaccine 100% effective against severe or critical symptomatic COVID-19. No safety concerns reported

Oxford coronavirus vaccine researcher Katie Ewer inspects samples in the lab © Photo by John Cairns

Our vaccine work is progressing quickly. To ensure you have the latest information or to find out more about the trial, please visit the Oxford COVID-19 vaccine web hub or visit the COVID-19 trial website.

A Phase III study of the Oxford-AstraZeneca coronavirus vaccine conducted by AstraZeneca plc in the USA, Chile and Peru has shown that vaccine is safe and highly effective, adding to previous trial data from the United Kingdom, Brazil and South Africa, as well as real-world impact data from the United Kingdom. 

In the trial, which recruited over 32,000 volunteers across all age groups, the participants received either two standard doses of the Oxford-AstraZeneca vaccine or a placebo vaccine, at a four-week interval. These data show that the vaccine is 79% effective against symptomatic COVID-19, and 100% effective against severe, or critical symptomatic COVID-19. 

These results also add to the extensive safety data collected both in previous trials and through real-world vaccine roll out schemes. The independent Data and Safety Monitoring Board (DSMB) reported no safety concerns among the participants receiving at least one dose of the vaccine.  

The absolute efficacy is higher in this new study than observed in the Oxford-led studies, as efficacy is affected by the protocol case definition (higher for more severe cases) and the population in which the study is conducted. Today’s findings are in line with findings from other major vaccine developers who studied efficacy in the US. 

Andrew Pollard, Professor of Paediatric Infection and Immunity, and Lead Investigator of the Oxford University trial of the vaccine, said: 

These results are great news as they show the remarkable efficacy of the vaccine in a new population and are consistent with the results from Oxford-led trials. We can expect strong impact against COVID-19 across all ages and for people of all different backgrounds from widespread use of the vaccine.  

Sarah Gilbert, Professor of Vaccinology, and co-designer of the ChAdOx1 nCov-19 coronavirus vaccine, said: 

‘These new results from the large phase III trials in the US, Chile and Peru provide further confirmation of the safety and effectiveness of ChAdOx1 nCoV-19. In many different countries and across age groups, the vaccine is providing a high level of protection against COVID-19 and we hope this will lead to even more widespread use of the vaccine in the global attempts to bring the pandemic to an end.’ 

AstraZeneca will be submitting the data for analysis by the scientific community in peer-review literature, and to the regulators in the USA, the US Food and Drugs Administration (FDA) and for emergency approval for use.

Similar stories

One billion doses: A moment to celebrate but not a time to be complacent

Professor Sir Andrew Pollard, Director of the Oxford Vaccine Group and Professor of Paediatric Infection and Immunity, takes a moment to reflect on one billion doses of the Oxford coronavirus vaccine released worldwide.

Severe disease, not mild infection, makes a pandemic – vaccines still offer our best hope

If the current high levels of protection against severe disease are sustained, the global public health emergency will be curtailed by the ongoing vaccine rollout - writes Andrew Pollard for The Independent.

Oxford vaccine reaches one billion doses released

The University of Oxford’s and our partners AstraZeneca have today announced that one billion doses of the ChAdOx1 nCov-19 coronavirus vaccine have been released, to more than 170 countries, marking a key milestone as part of the University and AstraZeneca’s joint vision to make the available to the world, on a not-for-profit basis for the world during the pandemic, and in perpetuity for low- and middle-income countries.

Oxford Vaccine Group among winners at NHS Parliamentary awards

Researchers behind the Oxford AstraZeneca coronavirus vaccine have been recognised for their excellence at a healthcare awards ceremony.

Mixed Oxford/Pfizer vaccine schedules generate robust immune response against COVID-19, finds Oxford-led study

Alternating doses of the Oxford-AstraZeneca and Pfizer-BioNTech vaccines generate robust immune responses against COVID-19, according to researchers running the University of Oxford-led Com-COV study.

Delayed second dose and third doses of the Oxford-AstraZeneca vaccine lead to heightened immune response

Research on the ChAdOx1 nCoV-19, also known as the Oxford-AstraZeneca vaccine, indicates that a long interval between first and second doses does not compromise the immune response after a late second dose.