How effective is AstraZeneca's coronavirus vaccine? We still don't have a clear, consistent answer. Since the fall, a string of studies — some peer-reviewed, others not — have suggested the vaccine could be anywhere from 22% to 90% effective, depending on the parameters. AstraZeneca's own trial results, released in November, were "awfully confusing for experts and non-experts alike," Natalie Dean, a biostatistician at the University of Florida, tweeted at the time. She gave the company "a poor grade for transparency and rigor." That's because the company combined data from its Brazil and UK trial groups, even though they had different sample sizes and demographics. AstraZeneca also averaged the results of two different dosing regimens, one of which was administered by mistake. Subsequent analyses, meanwhile, have revealed that only 12% of participants in AstraZeneca's late-stage trial were over 55, and that the vaccine's effectiveness varies dramatically depending on the time between the two doses. The company's own vaccine label says shots should be administered four...read more...