AstraZeneca will likely retest 

its COVID-19 vaccine, CEO

 says after admitting an error

 in the first trial 

A man walking past an AstraZeneca sign in Macclesfield, England. 

Phil Noble/Reuters

• The UK pharmaceutical company AstraZeneca is likely to run a second global trial to assess its COVID-19 vaccine's efficacy, its CEO told Bloomberg News on Thursday.
• AstraZeneca and the University of Oxford announced Monday that preliminary results indicated their two-dose vaccine could be up to 90% effective at preventing COVID-19.
• But the team later said an error in the trial left some participants with half-doses instead of full doses.
• Experts said that error cast doubt on the validity of the efficacy rate and warranted further study.