A further global trial is likely to be carried out on the Oxford University and AstraZeneca vaccine after an error in testing.
AstraZeneca is likely to take further steps to assess the effectiveness of its vaccine after a surprise result found 90 per cent protection was achieved when people were given a half dose followed by a full dose.
The firm has acknowledged the finding was as a result of a dosing error.
However, it says it does not expect any new trial to hold up regulatory approval in countries including the UK.
But addressing some of the claims levelled at AstraZeneca and Oxford at a Downing Street press conference tonight, Chris Whitty, England’s Chief Medical Officer, said: “The simple answer to this is there is always scientific debate about virtually everything. The key thing from our point of view is to leave this in the hands of the regulator, the excellent MHRA regulator.
“They will make an assessment with lots of data that is not currently in the public domain on efficacy and on safety and we will see the papers published in peer reviewed journals, which will allow us to makle a decision about what needs to happen.
“We need to allow that process to go forward. I think it’s always a mistake to make judgement early before we have enough information.”
One scientist said the “dosing error does throw up some problems” – and there have been some concerns about a lack of detail on the trials.
Another said it raised the need for caution over the effectiveness of the vaccine for older people.
Paul Hunter, professor of medicine at the University of East Anglia, told PA: “Given that many vaccines are less effective in older people, we have to be even more cautious about taking this 90 per cent efficacy at face value, at least for older people.”
However, many scientists have defended the work done – and one even said that the half-dose might end up being more effective.
The overall effectiveness from two different dosing regimes in a phase three trial was announced last week at a combined figure of 70 per cent.
A half dose then followed by a full dose was found to be 90 per cent effective, according to a subset of data.
However, the efficacy was 62 per cent for people given two full doses.
Earlier this week, Moncef Slaoui, the scientific head of the US’s Operation Warp Speed – the programme to supply America with vaccines – told media that the half-dose regime was only given to those aged 55 and under.
This is potentially problematic because scientists want to find vaccines that work in older people who are most at risk from Covid-19.
Results from an earlier phase two study published in The Lancet medical journal showed the vaccine had a strong response in all age groups.
Professor Andrew Pollard, director of the Oxford Vaccine Group, told reporters last week that the 90 per cent effectiveness finding had already met the “necessary statistical evidence as required by regulators”.
He said further evidence would probably be available next month but it is “a highly significant result even with the numbers that we have”.
The 90 per cent efficacy was based on a dosing regime for 2,741 people.
The other regime – involving two doses – involved 8,895 people.
However, Neither AstraZeneca nor Oxford revealed at the briefing that the 90 per cent figure was based on adults aged 55 and under.
Some US scientists have questioned a perceived lack of detail in the results put out last week by AstraZeneca and Oxford.
Some experts have raised questions about the use of two differently designed clinical trials in Britain and Brazil, and pooling analysis from both.
They have also said it is unclear how many Covid cases were found in each group of the trial.
The New York Times also said that AstraZeneca’s Menelas Pangalos had needed to defend the company’s handling of testing and its public disclosures.
John Moore, a professor of microbiology and immunology at Weill Cornell Medical College, told the New York Times: “The press release raised more questions than it answered.”
Mr Pangalos said the half-dose finding “could end up being quite a useful mistake”, adding: “What is there to disclose? It actually doesn’t matter whether it was done on purpose or not.”
The Oxford vaccine costs £2 to £3 per dose.
It can be more easily stored than vaccines from Pfizer/BioNTech and Moderna, which require very cold temperatures.
The jab is being assessed by the Medicines and Healthcare products Regulatory Agency (MHRA) for use in the UK.
In an interview with the PA news agency last week, Tom Keith-Roach, president of AstraZeneca UK, said there had been “highly statistically significant efficacy results in all subgroups… so I think the regulators will look at it on that basis”.
Helen Fletcher, professor of immunology at London School of Hygiene and Tropical Medicine (LSHTM), said: “What’s remarkable is that Oxford University and AstraZeneca have gone from square one to 100 million doses in less than a year.
“It’s not surprising if some manufacturing issues were still being ironed out when they started clinical trials but early stage trials are all about safety and the safety data we have seen has been very robust.”
She said it was important to wait for the full dataset to be published.
“I also think it’s possible that a lower initial vaccine dose could result in higher vaccine efficacy,” she said.
“More is not necessarily better when it comes to vaccines and immunotherapies. You need to stimulate an immune response but if you push too hard you can get hit a negative feedback loop where the immune system seeks to control and dampen down the response.
“It’s also possible that a strong immune response to the first vaccine could effectively block an immune response to the second shot of the same vaccine – but we should be able to see evidence of that when the data is published.”
Stephen Evans, professor of pharmacoepidemiology at LSHTM, said “the idea that no protocol has been published (by Oxford and AstraZeneca) is simply not true”.
He added: “The variety of age groups and dosing regimes is a feature of a number of the vaccine trials and not just the Oxford AstraZeneca vaccine.
“The way the data are put together will have been specified in the protocol and scrutinised very carefully by regulators to ensure that there is no ‘cherry picking’ of the results.”
Joy Leahy of the Royal Statistical Society said the scientific community was “rightly seeking more data in the form of a peer-reviewed paper”.
She said a press release was published due to the risk to financial markets from too many people knowing the results while awaiting peer-review publication.
She said the “dosing error does throw up some problems” and the 90 per cent result found may be due to random statistical variation.
“There are also some other complications in looking at this subgroup given that they were all in one location and apparently not representative of the full age profile in the trial,” she added.
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.
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