The Oxford coronavirus vaccine shows a strong immune response in adults in their 60s and 70s, according to encouraging early results.
Some 560 healthy adult volunteers took part in the phase two trials, where they were given two doses of the vaccine, or a placebo.
The COVID-19 vaccine developed by Oxford University produces a strong immune response in older adults, data from early trials has shown.
The UK has already ordered 100 million doses of the Oxford vaccine, manufactured by AstraZeneca, 40 million doses of the Pfizer-BioNTech vaccine and five million of the Moderna vaccine.
The phase one and phase two results from the Oxford/AstraZeneca trials suggest that one of the groups most at risk of death or serious illness from COVID-19 may be able to build immunity, according to data published in The Lancet medical journal.
It comes a day after Pfizer announced its coronavirus vaccine was 94% effective among adults over 65 in its final efficacy results, and that it would be seeking authorisation over the next few days.
No adverse health problems were reported during the trials, the report adds.
The University of Oxford said that across most vaccines, older adults tend not to be as well protected as younger adults, with antibodies induced by a vaccine often showing a lower protective capacity.
Dr Maheshi Ramasamy, an investigator at the Oxford Vaccine Group and consultant physician, said: “Older adults are a priority group for COVID-19 vaccination, because they are at increased risk of severe disease, but we know that they tend to have poorer vaccine responses.
“We were pleased to see that our vaccine was not only well tolerated in older adults; it also stimulated similar immune responses to those seen in younger volunteers. The next step will be to see if this translates into protection from the disease itself.”
Dr Angela Minassian, an investigator at the University of Oxford and honorary consultant in infectious diseases, added: “Inducing robust immune responses in older adults has been a long-standing challenge in human vaccine research.
“To show this vaccine technology is able to induce these responses, in the age group most at risk from severe COVID-19 disease, offers hope that vaccine efficacy will be similar in younger and older adults.”
The Oxford vaccine is made from a weakened version of a common cold virus (known as an adenovirus) from chimpanzees that has been modified so it cannot grow in humans.
Work began on the vaccine in January and it was developed in under three months, starting human trials – the first in Europe – in April in Oxford.
Phase three trials of the vaccine, which look at how effective it is at protecting people against the Covid-19, started at the end of August and are still continuing.
When data from this stage is sent to the regulators, scrutinised and approved, the vaccine can be given the green light to be used on people worldwide.