Full interim analysis of the safety and efficacy of the Oxford COVID-19 vaccine – developed in partnership with AstraZeneca – has been published in the Lancet. This paper represents the most comprehensive set of results from any of the phase 3 trials of COVID-19 vaccines to date. According to an article by Dr Paul Hunter, Professor of Medicine at the University of East Anglia in the UK, on the website of GAVI, the Vaccine Alliance, these are still only interim results, meaning they show only how the ongoing phase 3 trial has progressed so far. The final results may differ. But what this analysis reveals is how the Oxford team calculated its vaccine’s efficacy, which it announced in late November. This interim analysis included 11,636 people, of whom 7,548 were in the UK and 4,088 in Brazil, Dr Hunter writes. All participants received two injections, but as has been widely reported, one of the UK groups received a half dose rather than a full dose for the initial injection. This has made analysing the effects of this vaccine more complicated than it probably will be for others in the late stages of testing. Importantly, the evidence that the vaccine is safe is convincing, according to Dr Hunter. There were 175 severe adverse events reported in the trials, and these were actually more common in the control group (which received either saline or a meningococcal vaccine) than with those receiving the COVID-19 vaccine. Three of these events were judged to be possibly related to either the experimental or control vaccine. They included a case of transverse myelitis, a rare but serious spinal inflammatory disorder, in someone in the vaccine group, a case of haemolytic anaemia in someone in the control group, and a further person who developed a fever of over 40°C. As yet we don’t know whether this person received the COVID-19 vaccine or a control. Across the study, ten patients became sufficiently ill with COVID-19 to require hospitalisation, but all were in the control arm.