The jab showed an average efficacy of 70%, with the trial generating a 62% success rate when volunteers were given two full doses at least one month apart, but the chances of being protected from the virus rose to 90% when a half dose was administered followed a month later by a full dose.
Confusion over the trial
It is not clear why the lower dose, which is understood to have been administered by mistake, provokes a higher immune response.
Moreover, this ‘accidental’ trial only counted 2,300 participants, while competitors Pfizer Inc. (NYSE:PFE)/BioNTech and Moderna Inc. (NASDAQ:MRNA) reported over 90% efficacy for their candidates in trials of over 30,000 participants.
It was also revealed that all 2,300 participants were younger than 55, meaning they were less at risk from experiencing severe symptoms.
Not very transparent
This raised another concern around the lack of transparency by AstraZeneca, which did not disclose the details of this trial in Monday’s announcement with all the results.
“Given the disparity of the point estimates, we do think there is likely to be a real difference in efficacy between the two dosing regimens, but this can’t be proven until further data is accumulated to narrow these confidence intervals around the ‘true’ efficacy value,” analysts at Shore Capital noted.
“We are further evaluating the data and will work with regulators on the best approach for further evaluation,” a spokesperson told Proactive.
“This would add to data from existing trials which are currently being prepared for regulatory submission.”
In fact, chief executive Pascal Soriot told Bloomberg the pharma giant is mulling undertaking a new trial to confirm the efficacy rate, though this is not expected to cause delays to UK and EU approval.
The UK government, which has pre-ordered 100mln doses of the vaccine, has asked the medicines regulator to analyse whether the Oxford vaccine can get temporary authorisation, though it is still subject to the European authorities approval until Brexit takes place in January.
Questions over US approval
Meanwhile, members of the scientific community have said the Food and Drug Administration is unlikely to issue approval with the current data, especially since the trials didn’t take place in the US.
John LaMattina, former senior executive at Pfizer, said it is “hard to believe” that the US authorities will issue an emergency use approval.
AstraZeneca and the University of Oxford have defended their vaccine because the lowest efficacy rate of 62% is still higher than the 50% required by the World Health Organisation and the US Food and Drug Administration, while there were no cases of severe COVID-19 or hospitalisations.
“When taken in totality, we think it’s fair to say that AZD1222 [the vaccine] hasn’t produced any concerning safety signals linked to the vaccine (although we await the full data) and that it is efficacious to some degree,” ShoreCap said.
“It is clear that evidence of a potentially more effective dosing regimen needs to be investigated and confirmed, given it wouldn’t be sensible to ignore an opportunity to possibly increase the vaccine efficacy to around 90% at a lower dose.”
“Similarly, even if you believed the half dose/full dose regimen was truly more efficacious, it wouldn’t be sensible to offer people the half dose/full dose regimen, without actually knowing how efficacious it is, as this is clearly a big factor in deciding which (if any) vaccine an individual would choose if given a choice (especially as there was no-one studied over the age of 55 in the half dose/full dose arm).”
Shares in the firm dipped 1% to 7,680p on Friday afternoon, having shed 8% over the week.