The jab could be licenced for use in the elderly, the lead researcher of the trial has said.
Sarah Gilbert, professor of vaccinology at the university, said there were no timings on when the Medicines and Healthcare products Regulatory Agency (MHRA) would approve the jab Oxford is developing with AstraZeneca.
She added that it is for regulators to decide whether to give permission for vaccine use based on a smaller subgroup – who were given a half dose followed by a full dose – which had higher efficacy results.
The subgroup is smaller than the subgroup that received two full doses, and included no older adults.
Dr Gilbert told BBC Radio 4’s Today programme: “In the whole trial we haven’t had many cases of Covid disease in older people because they were recruited later into the trial.
“So the data that’s analysed so far was collected by the beginning of November, and in the next data analysis it’s likely there’ll be more inclusion of people over the age of 55.”
The team has measurements on the immune response in older people, she said, adding: “It doesn’t decline at all in people – even over the age of 70 there was no difference in their immune response.”
Asked if this meant the MHRA could support licensing the vaccine for the elderly, Dr Gilbert said: “Yes, they could decide to do that.”
Dr Gilbert said researchers need to look into different immune responses among people who have different vaccination regimens and see if they can find an explanation.
The UK has secured 100 million doses of the Oxford-AstraZeneca vaccine which can be stored between 2C and 8C.
The Pfzier vaccine, which the NHS began rolling out on Tuesday, needs storage temperatures of minus 70C to minus 80C, but can be stored under normal refrigerated temperatures for five days.
This has created challenges in trying to get the vaccine to care homes, and despite being identified as a top priority for vaccines, care home residents have not been included in the initial rollout.
England’s deputy chief medical officer Jonathan Van-Tam has suggested people who cannot leave their homes may need to wait for the Oxford-AstraZeneca vaccine.
The published interim phase three results of the Oxford vaccine trials found the jab protects against symptomatic disease in 70% of cases – with efficacy of 62% for those given two full doses, and 90% in those given a half then a full dose.
The Pfizer vaccine has shown an efficacy of 95%.
Experts have suggested it may be necessary to simply use the vaccines that are approved and that the UK has access to.
Kate Bingham, chairwoman of the vaccine taskforce, has said securing more doses “depends by contract”, and while there are options to extend some, others are for a fixed number of doses.
Professor Andrew Pollard, director of the Oxford Vaccine Group and chief investigator of the Oxford trial, said on Tuesday: “Personally I think we need to be completely agnostic about which vaccine is being used because we need multiple vaccines, as soon as possible.
“Otherwise we’ll still be in this position in six months’ time.”