People who have been double-dosed with the Oxford-AstraZeneca vaccine could have a stronger immune response if they were given a different jab as a booster, a leading scientist has said.

Professor Matthew Snape from the Oxford Vaccine Group said the “mix and match” approach may result in additional protection against coronavirus.

He made the comments following the results of a clinical trial comparing the current UK strategy of giving two doses of either the AstraZeneca or Pfizer/BioNTech vaccines against a combination of the two jabs.

Results showed people who received the AstraZeneca vaccine first, followed four weeks later by a Pfizer dose, produced antibody levels nine times higher than those given two doses of the Oxford jab.

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Volunteers who were given Pfizer first and AstraZeneca second had antibody levels five times higher than those who received two doses of the Oxford vaccine.

Two doses of the Pfizer jab produced the highest antibody levels, but the T-cell response was higher in people receiving the combination of vaccines.

Prof Snape, who led the Com-CoV study, said the combination gives “an extra kick to the immune system”.

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He said: “When it comes to the coming winter, if a third dose was to be given, then these are really important data to inform which vaccines we should be using and which combinations we should be using.

“From our study you have to be thinking that if you received AZ/AZ (for the first and second doses) then maybe there would be advantages in getting an RNA vaccine (Pfizer or Moderna) next.”

Another study, called Cov-Boost is currently testing combinations of booster shots for people who’ve received either two doses of the AstraZeneca or Pfizer vaccines.

Results are expected by September, in time for a booster campaign this autumn and winter, if it is needed.

Prof Snape said further results from his study are expected next month testing the mix-and-match approach with an eight to 12 week gap between the first and second doses, the current schedule in the UK.

Scientists believe the immune response to the AstraZeneca vaccine is a slow-burn and the extra time between the doses may prove more effective.

Deputy chief medical officer, Professor Jonathan Van-Tam, said the UK would stick to its current rollout using the same vaccine for the first and second dose.

“Given the UK’s stable supply position there is no reason to change vaccine schedules at this moment in time,” he said.

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However, he added that the new data “are a vital step forward”.

“The results for the 12-week interval, which are yet to come, will have an instrumental role to play in decisions on the future of the UK’s vaccination programme.”

Earlier research has shown that using a combination of vaccines leads to more mild or moderate side effects such as headache and fever, which lasted a day or two.

The study has been published by The Lancet as a pre-print.

Meanwhile, one of the Oxford vaccine’s developers has said there is no evidence a third Oxford-AstraZeneca jab is needed at the moment – despite new research suggesting it restores peak immunity.

Research by the University of Oxford team that developed the vaccine has shown a booster at least six months after the second jab brings immunity levels back to their peak – and significantly increases antibody and T-cell levels to the virus, including variants.

But the director of the Oxford Vaccine Group, Professor Sir Andrew Pollard, said the priority should be ensuring people in other countries have had at least one dose.

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