Disquiet is growing over the way that Oxford university and AstraZeneca have handled the early readout from trials of their coronavirus vaccine, which much of the developing world may rely on to emerge from the pandemic.
The results were hailed a success for showing an average efficacy of 70 percent — a figure reached by pooling the results from cohorts on two different dosing regimens.
One set of participants received two identical doses a month apart, while the other group received a half-dose, and then a full dose. The efficacy for the first, larger group was 62 percent. In the second subgroup, it was 90 per cent.
It has emerged that administration of the half-dose started with a mistake. It was then given to a smaller number of participants than those who received two full doses, making the discovery of its greater effectiveness look like a lucky break.
Yet on Tuesday, Moncef Slaoui, the head of Operation Warp Speed, the US government’s funding program for vaccine development, disclosed that the second subgroup was also limited to people aged 55 or below, a demographic with a lower risk of developing severe Covid-19.
Oxford and AstraZeneca did not disclose the age breakdown on Monday, when results were released.
“There are a number of variables that we need to understand,” Mr Slaoui said. It is still possible the difference in efficacy was “random”, he added.
Markets have taken notice. London-listed shares in AstraZeneca have lost more than 6 per cent since the announcement. By comparison, since trial results from their vaccine were released earlier this month, showing an effectiveness of 90 per cent, shares in Pfizer and BioNTech have gained 6 per cent and 14 per cent respectively; Moderna is up 11 per cent since its vaccine trial data came out, on top of big gains in the run-up to publication.