LONDON – AstraZeneca and Oxford University on Wednesday acknowledged a manufacturing error that is raising questions about preliminary results of their experimental COVID-19 vaccine.A statement describing the error came days after the company and the university described the shots as “highly effective” and made no mention of why some study participants didn't receive as much vaccine in the first of two shots as expected.[TRENDING: Puppy pried from gator’s mouth doing OK | Florida Rep says Trump should pardon himself | 15-year-old girl dies after overdosing]In a surprise, the group of volunteers that got a lower dose seemed to be much better protected than the volunteers who got two full doses.