AstraZeneca (AZN  ), in partnership with Oxford University, reported robust efficiency results for its potential coronavirus vaccine last Monday. However, those results were met with concerns from experts, including the World Health Organization and scientists within the University of Oxford, over the clinical trial's methods.

The drugmaker's late-stage trial results found that the vaccine was up to 90% effective from two different dosing regimens, but was 70% effective on average. Concerns were raised after the company revealed that a small group participants, all under the age of 55, were given an unintentional lower dosage of the vaccine in their first shot. That smaller dosing regimen was found to be 90% effective compared to participants who received two full doses of the vaccine. This trial error led to questions over the trial's methodology and the drugmaker's transparency.

The main concern raised by global health authorities was that the high efficiency demonstrated in the trial's results was seen only in participants under the age of 55, or those less likely to be severely affected by the coronavirus. AstraZeneca's vaccine was praised earlier for being similarly effective in across all adult age groups in mid-stage trials, including those over the age of 70.

To clear up this raised uncertainty, AstraZeneca and Oxford University plan to begin an additional global trial, with the new study's goal being to confirm the 90% efficacy rating, according to AstraZeneca's Chief Executive Officer Pascal Soriot in an interview with Bloomberg News.

"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. This was his first interview since the trial's data was released. Soriot noted that the new international trial could progress more quickly than previous studies, "because we know the efficacy is high, so we [will] need a smaller number of patients."

Soriot added that he does not expect the extra trial to effect the vaccine's timeline for regulatory approvals in the United Kingdom and the European Union, with the drug expected to be approved for public use by the end of the year. However, the vaccine may take longer to gain approval from the U.S. Food and Drug Administration (F.D.A.) due to the vaccine's trial data coming from studies outside of the United States, especially due to the concerns surrounding the results.

AstraZeneca and Oxford researchers have declined to provide any more data on the vaccine's clinical trials ahead of peer review analysis that is expected to be published within the next few weeks.

Since the beginning of the vaccine's confusion, AstraZeneca's stock have declined. Market participants have begun to bet on Mondera's (MRNA  ) shot being the "winner" of the coronavirus vaccine race due to its slight distribution advantage over Pfizer's (PFE  ) and BioNTech's (BNTX  ) potential candidate.