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UK COVID-19 vaccine is 90% effective using one dosage regimen, trial data suggest

The half dose followed by a full dose regimen of the vaccine being developed by Oxford University and AstraZeneca has the highest effiicacy, data from phase II/III trials indicate.

Open access article

The Royal Pharmaceutical Society has made this article free to access in order to help healthcare professionals stay informed about an issue of national importance.

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University of Oxford


Oxford University will be submitting full analysis of the vaccine trial data for peer review and publication

The COVID-19 vaccine being developed by Oxford University is up to 90% effective in preventing COVID-19 symptoms, interim analysis of trial data suggests. 

The UK government has pre-ordered 100 million doses of the vaccine. 

Pooled data from phase II/III trials carried out in the UK and Brazil, released on 23 November 2020 by Oxford University and its manufacturing partner AstraZeneca, include 131 COVID-19 cases, with 30 in the vaccine group and 101 in the placebo group. 

The vaccine, known as ChAdOx1 nCoV -19 or AZD1222, uses a genetically weakened version of a chimpanzee adenovirus to carry the genetic code for surface spike protein on SARS-CoV-2 into the cells of the body. 

In the trials, which involved more than 24,000 participants from diverse racial groups, the vaccine was given in two regimens: two full doses, or a half dose followed by a full dose. In the full dose/full dose arm, which involved 8,895 participants, the vaccine prevented 62% of cases, and in the half dose/full dose arm, which included 2,741 participants, it prevented 90% of cases, giving an overall efficacy of 70.4%. 

There were no hospitalisations or severe cases in any participants who received the vaccine, and it was well tolerated with no serious safety events identified.  

“We think that by giving a smaller first dose, we’re priming the immune system differently; we are setting it up better to respond,” Andrew Pollard, director of the Oxford Vaccine Group and chief investigator of the Oxford vaccine trial, told a news conference to announce the trial’s results.   

Unlike the mRNA vaccines from Pfizer/BioNTech and Moderna, which must be stored in a freezer, the Oxford vaccine can be stored at between 2 and 8 degrees Celsius.  

The clinical trials will now continue to final analysis. Further trials are being conducted in the United States, Kenya, Japan and India, with up to 60,000 participants expected to be enrolled by the end of 2020.  

Rolling submissions for licensing are ongoing with both the Medicines and Healthcare products Regulatory Agency in the UK and the European Medicines Agency, and Oxford is submitting full analysis of the trial data for independent scientific peer review and publication.

Citation: The Pharmaceutical Journal DOI: 10.1211/PJ.2020.20208575

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