What We Know About AstraZeneca’s Head-Scratching Vaccine Results

 https://www.nytimes.com/2020/11/24/health/astrazeneca-covid-vaccine.html

Surprisingly, the vaccine combination in which the first dose was only at half strength was 90 percent effective at preventing Covid-19 in the trial. In contrast, the combination of two, full-dose shots led to just 62 percent efficacy.

Fewer than 2,800 volunteers got the half-strength initial dose, out of the more than 23,000 participants whose results were reported on Monday. That’s a pretty small number of participants on which to base the spectacular efficacy results — far fewer than in Pfizer’s and Moderna’s trials.