After admitting mistake, AstraZeneca faces hard questions about vaccine

But since unveiling the preliminary results, AstraZeneca has acknowledged a key mistake in the vaccine dosage received by some study participants, adding to questions about whether the vaccine’s apparently spectacular efficacy will hold up under additional testing.

Scientists and industry experts said the error and a series of other irregularities and omissions in the way AstraZeneca initially disclosed the data have eroded their confidence in the reliability of the results.

Officials in the United States have noted that the results were not clear. The head of the flagship federal vaccine initiative suggested that the vaccine’s most promising results may not have reflected data from older people.

The upshot, the experts said, is that the odds of regulators in the United States and elsewhere quickly authorizing the emergency use of the AstraZeneca vaccine are declining, an unexpected setback in the global campaign to corral the devastating pandemic.