Concerns around the efficacy of the Oxford University/AstraZeneca coronavirus jab in older people could lead to different age groups being given different vaccines, experts have said.
The partners announced last week that the vaccine had a 70% efficacy overall. For most trial participants – given two full doses, spaced a month apart – the efficacy was 62%, but for 3,000 participants mistakenly given half a dose for their first jab, the efficacy was 90%. No participants, regardless of dosing, developed severe Covid or were hospitalised with the disease.
Regulators such as the US FDA have previously said they would approve a vaccine that prevents Covid or reduces disease severity in at least 50% of vaccinated people.
The Oxford University/AstraZeneca results caused much excitement, with the 90% efficacy figure rivalling those of vaccines from Moderna and Pfizer/BioNTech.
Unlike its rivals, the Oxford vaccine is cheap to produce and does not need to be stored at very cold temperatures. It also accounts for 100m of the 355m vaccine doses to which the UK government has secured early access.
However, it has emerged that the group that received the low dose of the Oxford University/AstraZeneca vaccine did not include any participants over the age of 55, meaning it is unclear whether the 90% efficacy holds for older adults, who are at higher risk from Covid.
This has led AstraZeneca to announce a new global trial using the lower-dose regimen, although this is not expected to affect the timeline for regulatory approval and rollout of the vaccine in the UK and Europe.
Speaking on BBC Radio 4’s Today programme, Prof David Salisbury, a former director of immunisation at the Department of Health, said the further trials were important.
“If this vaccine came through at truly 90% and it is a cheaper vaccine and it requires much less rigorous cold chain than the RNA vaccines [from Moderna and Pfizer/BioNTech], then that would be a great result,” he said.
“But if it comes through at 62% and the other vaccines that are coming through so far are coming through at 90% then I think you have to think very carefully, what do we do with 100m doses of a product that isn’t protecting as well as the alternatives.”
That could lead to tough decisions, he said. “I think it starts to give you some feel of how you prioritise the use of your vaccines, and you may well want to think about the higher-efficacy vaccines in the higher-risk people where you really do want to protect them,” he said.
Prof Helen Fletcher, a professor of immunology at the London School of Hygiene & Tropical Medicine, told the Guardian that it was likely that AstraZeneca and Oxford would seek a licence for the full-dose regime, which protects 62% of people from developing Covid.
“They have immunised a much larger number of people with the higher doses and importantly this includes the older people who are more at risk of serious disease,” she said. “The dataset for the lower-dose regimen might not be large enough for licensure as it stands, so it makes sense to do another trial with the lower dose – including older people – and seek an amendment for use of this dose when they have enough data.”
But Fletcher agreed it made sense to look at all the available vaccines when it comes to an immunisation programme. “With multiple vaccines available, I think it’s right for policymakers to think about which vaccines might work best in which populations,” she said. “This is not unusual: we give three different types of flu vaccine in the UK to children, young adults and the elderly, as we know that different vaccine platforms work better in different age groups.”
Dr Penny Ward, a visiting professor in pharmaceutical medicine at King’s College London, said: “I personally view this [Oxford/AstraZeneca] vaccine (and the others) as being like the influenza vaccination – ie they do not protect from infection but can reduce the severity of disease and, importantly, the risk of severe complications and death.
“It is relevant here to note that influenza vaccination is 50-60% effective in most seasons but nonetheless reduces severity of disease and need for hospitalisation in the vaccinated older age population. Given that the target was 50% efficacy for the Covid vaccines, and that the Oxford vaccine has exceeded that target, then it seems likely to be useful for helping diminish the need for hospitalisation and mortality.”