AstraZeneca has said it will most likely carry out a further global clinical trial to assess the efficacy of its Oxford University Covid-19 vaccine after a surprise result found 90% protection was achieved when people were given a half dose followed by a full dose.
The pharmaceutical giant has acknowledged the finding was as a result of a dosing error, but it did not expect any new trial to hold up regulatory approval in countries including the UK.
Moncef Slaoui, the scientific head of the US’s Operation Warp Speed – the programme to supply America with vaccines – told US reporters the half-dose regime was only given to people aged 55 and under.
This could pose problems as scientists across the globe are hoping to find vaccines that work in older people who are most at risk from Covid-19.
But ITV News Science Editor Tom Clarke said the UK regulator Medicines and Healthcare products Regulatory Agency (MHRA) will scrutinise the data and make an "unbiased judgement" on the efficacy of the vaccine.
"The Oxford vaccine trial was designed in a complicated way partly to make sure they got results as quickly as they could. That means the data is quite messy," he said.
"That has led to some in the US to raise questions about whether the claims they made in a press release on Monday can be substantiated by that data. But actually they are no better qualified than you or I are because none of us, including them, have seen the data yet."
Watch ITV News Science Editor Tom Clarke's analysis on the concerns raised:
He added: "It's also important to point out that the American data has not been published either.
"Ultimately the fact that all this scrutiny is there is a good thing because we are going to get the safest, most trusted vaccine that we all deserve."
Results from an earlier phase two study published in The Lancet medical journal showed the vaccine produced a strong response in all age groups.
Professor Andrew Pollard, director of the Oxford Vaccine Group, told reporters at a UK-based press briefing last week that the 90% effectiveness finding had already met the “necessary statistical evidence as required by regulators”.
He said further evidence will probably be available next month but it is “a highly significant result even with the numbers that we have”.
The 90% efficacy was based on a dosing regime given to 2,741 people. The other regime (two doses) involved 8,895 people.
The Oxford vaccine is only £2 to £3 per dose and can be more easily stored than vaccines from Pfizer/BioNTech and Moderna, which require very cold temperatures.
A spokesman for AstraZeneca told PA on Thursday: “As the development of the vaccine was scaled up into the Oxford-sponsored Phase II/III trial, the measurement used for earlier trials was shown to over-estimate the strength of dose in the new larger batches, resulting in a half dose of the vaccine being administered.
“This was reviewed by the independent Data Safety Monitoring Board and the UK regulator, both of whom approved the continuation of this dosing regimen and the regulator publicly confirmed that there was ‘no concern’.
“All other regulatory authorities were informed that we would continue to monitor and study this cohort. Given the high efficacy we have now seen with the different dosing regimens, there is strong merit in continuing to further investigate these findings in order to establish the most effective dosing regimen.
“We are in discussions with regulators around the world to evaluate these findings and we look forward to the publication of the peer-reviewed results, which has now been submitted to the journal.”
Oxford University said it would not comment ahead of the data appearing in a peer-reviewed publication.
In a Downing Street briefing, England’s chief medical officer Professor Chris Whitty said the “excellent” MHRA would assess all data, including that not in the public domain, adding “there is always scientific debate about everything”.