AstraZeneca will likely retest its COVID-19 vaccine, CEO says after admitting an error in the first trial that may have skewed results
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.
Experts' trust in the validity of AstraZeneca's reported COVID-19 vaccine data has quickly eroded.
AstraZeneca and the University of Oxford said on Monday that their coronavirus vaccine was found to be up to 90% effective based on preliminary results from studies of 23,000 volunteers in Brazil and the UK.
But reports of an error during its initial trial prompted a barrage of questions.
On Thursday, the pharmaceutical company's CEO, Pascal Soriot, acknowledged the concerns and said it would likely conduct a second trial of the two-dose vaccine, Bloomberg News first reported Thursday.
"Now that we've found what looks like a better efficacy we have to validate this, so we need to do an additional study," Soriot told Bloomberg News.
The error meant about 2,700 participants got 1 1/2 vaccine doses instead of the intended two. That actually resulted in a higher efficacy rate in that group than among those who got the prescribed amount.
Soriot said that to clarify this discrepancy and meet the public-health community's demand for more data, AstraZeneca would likely run another "international study" to examine the strength of the half-dose/full-dose regimen among more participants.
"But this one could be faster because we know the efficacy is high so we need a smaller number of patients," he added.
Experts question AstraZeneca's data
AstraZeneca is the third company to report positive initial results from late-stage studies. Moderna and Pfizer said earlier this month that their vaccines were found to be 94.5% and 95% effective.
AstraZeneca's efficacy rate, however, was more complicated.
A dosing error during its trial resulted in about 2,700 participants receiving a half-strength dose followed by a full-strength dose. In that subgroup, the vaccine was 90% effective at preventing COVID-19, AstraZeneca said.
But in a group of about 9,000 participants who received two full-strength doses, that efficacy rate dropped to 62%.
Confused experts tried to interpret this broad range in efficacy, but that turned sour when AstraZeneca announced that the most effective regimen was an accident.
Sheila Bird, a biostatistician from the University of Cambridge's Medical Research Council, told Politico on Thursday that "this is a considerable complication" because the half-dose/full-dose regimen "occurred in error" and was not by design.
Moncef Slaoui, the head of the US's Operation Warp Speed vaccine-development program, also pointed out that the small group didn't include any participants over the age of 55, which could explain why the vaccine was more effective at preventing COVID-19.
Others accused the company of "cherry-picking" data to make it seem as if the vaccine had a higher efficacy rate and of not being transparent about how it arrived at its 70% average efficacy figure, Wired reported on Wednesday.
All three vaccine frontrunners are still experimental. None of the companies has published results in a medical journal, and US regulators have not authorized any of the shots for emergency use, let alone given them full approval.
Andrew Dunn contributed reporting to this story.
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