Preliminary data suggest that the immunization was more effective in trial participants who received a lower dose.
A highly anticipated COVID-19 vaccine has delivered some encouraging — but head-scratching — results. The vaccine developed by the University of Oxford, UK, and pharmaceutical giant AstraZeneca was found to be, on average, 70% effective in a preliminary analysis of phase III trial data, the developers announced in a press release on 23 November.
But the analysis found a striking difference in efficacy, depending on the amount of vaccine delivered to a participant. A regimen consisting of two full doses given a month apart looked to be just 62% effective. But, surprisingly, participants who received a lower amount of the vaccine in a first dose and then the full amount in the second dose were 90% less likely to develop COVID, compared with participants in the placebo arm.
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