Questions over AstraZeneca's COVID-19 vaccine data

British drugmaker AstraZeneca is working with regulators to investigate a lower dosage of its vaccine that performed better than a full dosage, a spokesman for the company said on Thursday, after its chief executive was quoted as saying an additional global trial was likely.

This report produced by Jillian Kitchener.

AstraZeneca is working with regulators to investigate a lower dosage of its experimental COVID-19 vaccine that performed better than a full dosage.

That’s according to a spokesman for the company, who made the statement after its CEO was quoted as saying an additional global trial was likely - instead of adding the trial to an ongoing U.S. process.

Asked about a Bloomberg report which quoted CEO Pascal Soriot, an AstraZeneca spokesman said : "As we communicated earlier this week, there is strong merit in continuing to further investigate the half-dose/full dose regimen." News of a likely additional trial comes as AstraZeneca faces questions about its success rate that some experts say could harm its chances of getting speedy U.S. and EU approval.

Several scientists have cast doubts on results released Monday showing the experimental vaccine was 90% effective in a sub-group of trial participants who, by error initially, received a half dose followed by a full dose.

AstraZeneca told Reuters earlier on Thursday that administering of the half dose had been reviewed and approved by independent monitors and the UK regulator.

Clearance from the U.S. Food and Drug Administration may take longer though because the agency is unlikely to approve the vaccine based on studies carried out elsewhere, according to Soriot, especially given the questions over the results.