Disquiet is growing over the way that Oxford university and AstraZeneca have handled the early readout from trials of their Covid-19 vaccine.
But since unveiling the preliminary results which showed up to 90-percent efficacy, AstraZeneca has acknowledged a key mistake in the vaccine dosage received by some study participants, adding to questions about whether the vaccine's efficacy will hold up under additional testing.
AstraZeneca admitted that researchers gave only half a dose by mistake, and the fact that it worked was "serendipity."
Its effectiveness could be as low as 62 percent.
Also, all the participants were younger than 55, raising doubts about whether it'll work for older people.