Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK
Interim results from 4 studies (11,636 participants from 23,848 participants overall) found an efficacy rate of 62.1% and 90% for those who received two standard doses, and those who received a low dose followed by a standard dose. The overall efficacy rate was 70.4%.
Source:
The Lancet
SPS commentary:
From 21 days after the first dose, there were ten cases hospitalised for COVID-19, all in the control arm; two were classified as severe COVID-19, including one death.
From 74 341 person-months of safety follow-up there were 84 adverse events reported with the vaccine vs 91 in the control group. Three events were classified as possibly related to a vaccine; one in the vaccine group, one in the control group, and one in a participant who remains masked to group allocation.
A related commentary discusses this report of the Oxford–AstraZeneca chimpanzee adenovirus vectored vaccine ChAdOx1 nCoV-19. It highlights some salient points, including the fact that that after phase 1 results supported a two-dose regimen, the trial protocols were amended where necessary to require two standard doses administered 28 days apart, but a subset in one of the UK trials inadvertently received a half-dose of the vaccine (low dose) as the first dose before a change in dosage quantification methodology. Additionally, the protocol amendments enabled other trial participants originally scheduled to receive a single dose to receive a booster more than 28 days after their first dose.
Also, only 12·1% of those assessed for efficacy were older than 55 years (none of whom were in the low dose/standard dose cohort), meaning that from the interim analysis of these trials, efficacy in older adults, who are the group at greatest risk of severe COVID-19 outcomes, cannot yet be inferred.