Oxford COVID-19 Vaccine Trial Results Mixed

Tim Locke

December 08, 2020

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Phase 3 interim trial results from the Oxford/AstraZeneca vaccine have just been published in The Lancet. Previously, interim results were issued in a press release.

In today's paper, for participants who received two standard doses, vaccine efficacy was 62.1%.

In participants who received a low dose followed by a standard dose, efficacy was 90.0%.

This was described as "intriguingly high compared with the other findings in the study. Although there is a possibility that chance might play a part in such divergent results."

Professor Andrew Pollard, director of the Oxford Vaccine Group, Department of Paediatrics, University of Oxford, told a news briefing hosted by the Science Media Centre that the half dose, full dose approach that gave the best results wasn't planned. He dismissed concerns about the age of participants in that group saying the result "doesn't appear to be an age phenomenon".

Overall vaccine efficacy across both groups was 70.4%.

Regulators and UK vaccination advisers would have to assess which regimen might be selected for approval, Prof Pollard said.

The vaccine was found to be safe, the authors said, with only three out of 23,745 participants over a median of 3.4 months experiencing serious adverse events that were possibly related to a vaccine; one in the vaccine arm, one in the control arm, and one in a participant who remains masked to group allocation. All participants have recovered or are recovering, and remain in the trial.

The paper said: "A case of transverse myelitis was reported 14 days after ChAdOx1 nCoV-19 booster vaccination as being possibly related to vaccination, with the independent neurological committee considering the most likely diagnosis to be of an idiopathic, short segment, spinal cord demyelination."

Prof Pollard said: "I think today is an important landmark for us because the data package that is in this paper is being put forward to regulators to consider and to scrutinise so there's these two different aspects of scrutiny, there's the scientific peer review for publication, and also the regulatory processes which I'm sure we'll hear more about in the weeks ahead."

Professor Sarah Gilbert, Jenner Institute, Nuffield Department of Medicine, University of Oxford, said: "This is a really good day in the UK. This is probably the best day we've had in 2020. Not only today are we seeing the first rollout of NHS vaccinations against COVID-19, from our side we're able to present to you our data in a full peer reviewed publication."


In a linked comment, Dr Maria Deloria Knoll and Dr Chizoba Wonodi, Johns Hopkins Bloomberg School of Public Health, USA, who were not involved in the study, said: "Despite the outstanding questions and challenges in delivering these vaccines, it is hard not to be excited about these findings and now the existence of three safe and efficacious COVID-19 vaccines, with 57 more in clinical trials."

Professor Stephen Evans, professor of pharmacoepidemiology, London School of Hygiene & Tropical Medicine, commented: "These results reflect the headlines given in previous press releases, but with both a fuller explanation of what was done and more detail around the uncertainty in the estimates of efficacy.

"The unfortunate [half dose] measurement technique problem that occurred with some doses produced in Italy is going to be seen by some as raising questions about this trial. It is clear however, that national and international regulators were fully apprised of what had happened and a plan for analysis was determined prior to knowledge of the results." 

This article originally appeared on Medscape UK, part of the Medscape Professional Network.

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