AstraZeneca’s missteps and murky data sewed worldwide confusion that undermined trust – but don’t rule the shot out yet

AstraZeneca’s missteps and murky data sewed worldwide confusion that undermined trust – but don’t rule the shot out yet

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 to 12 weeks apart. 

This confusion has led to a patchwork of mismatched vaccine authorizations and guidelines around the world.

On Wednesday, a World Health Organization panel recommended the shot for all adults. But several European nations haven't cleared the vaccine for