Expert reaction to press release from AstraZeneca announcing interim data on safety and efficacy from the US trial of the Oxford-AstraZeneca COVID-19 vaccine


(Source: Science Media Centre) –

AstraZeneca has published a press release announcing that the Oxford-AstraZeneca COVID-19 vaccine US Phase III trial met primary efficacy endpoint in preventing COVID-19 at interim analysis.

Dr Andrew Garrett, Executive VP, Scientific Operations, ICON Clinical Research, said:

“This is clearly stated as an AstraZeneca-led trial, and it more closely follows the large phase III vaccine trials reported by other sponsors.  In this respect it is a solid 30,000 plus participant study with a placebo control, and a simple 4 week dosing interval, such that interpretation is more straightforward than previous Oxford/AZ vaccine trials.  It has a good age mix with more than 6,000 participants aged >65 years and also wide ethnic representation.  Interim efficacy is clearly stated as being 79% against symptomatic COVID-19 and 100% effective against severe disease.  Detailed numbers are not provided at this time and the lower confidence limit is not stated.  Importantly the trial provides further support for efficacy in the elderly (80%) where previous clinical trial data, other than immunological data, had been lacking.  The study randomized two subjects to receive vaccine for every subject that received placebo providing a large safety database of 20,000 plus participants who received active vaccine.  As described, this has been used to investigate the potential association of the vaccine with thrombotic events and specifically cerebral venous sinus thrombosis, of which there were no cases detected.  Overall it was reported that there was no increased risk of thrombosis.  These data are therefore timely in further addressing any safety concerns that could undermine vaccine uptake.

“The trial is directed at generating data to support emergency use in the US but also provides valuable data to other countries – both confirming efficacy using a 4-week dosing interval and re-enforcing vaccine safety.”

Prof Stephen Evans, Professor of Pharmacoepidemiology, London School of Hygiene & Tropical Medicine, said:

“These results are not surprising given what we know now.  The US regulatory authorities are reluctant, even in a pandemic, to rely totally on data obtained outside the US, so this trial was done to provide convincing evidence of efficacy and safety in a sufficiently large number of US patients.  The benefits of these results will mainly be for the rest of the world where confidence in the AZ vaccine has been eroded, largely by political and media comment.  Once that happens, reporting of adverse effects becomes very biased and confidence can spiral downwards.  The rest of the world that will rely on this low-cost vaccine may be able to procced with vaccinating their populations.

“Vaccine development and rollout should be an international collaboration rather than nationalistic fervour whether in favour of, or against, a particular vaccine.  Assessment should be based on science alone.

“It is important also to realise that the “headline” efficacy numbers are valid for comparison between the groups in a trial, but great care is needed in comparisons between trials.  The way that events are assessed and counted as well as the context of a trial means that exact values for any between trial comparison are uncertain, not only because of statistical uncertainty, but also because of these other factors.

“It is clear this vaccine has very good efficacy (remember that 60% was, prior to any trials being started, regarded as a good target), and that this efficacy does not show a notable decline at older ages.  This was expected and the speculation that it was ineffective (or “quasi-ineffective”) at older ages was totally unjustified.

“This is good news for the global community and one hopes that any political statements around this good news are avoided.”

AstraZeneca press release:

University of Oxford press release:

All our previous output on this subject can be seen at this

Declared interests

Dr Andrew Garrett: “I am employed by ICON which is a Contract Research Organization.  ICON provides pharmaceutical services to the pharmaceutical and biotechnology industries. ICON conducts clinical trials on behalf of Sponsors, including vaccine trials. I am a member of the UK Statistical Authority’s (UKSA) Research Accreditation Panel. I have received one dose of the Oxford/AstraZeneca vaccine as part of the UK vaccination program.”

Prof Stephen Evans: “No conflicts of interest.  I am funded (one day per week) by LSHTM.  They get funding from various companies, including Astra Zeneca and GSK but I am not funded by them, I have no involvement in obtaining funding from them and I am not an investigator on any grants obtained from them.  I am the statistician to the ‘meta-Data Safety and Monitoring Board’ for CEPI.  I am paid for my attendance at those meetings and will be paid expenses for travel if that occurs.  I am a participant in the Oxford/Astra Zeneca trial, and on 13th January 2021 learnt I had received the active vaccine.”


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