AstraZeneca and Oxford University did not immediately respond to a request for comment on Oxford's yet to be published study.
The vaccine makes use of a new technology employing a modified version of adenoviruses, which cause the common cold, as vectors to ferry instructions to human cells.
This design led to concern among scientists that the doses could lose potency if annual inoculations become necessary to fight new variants.
It is not known when Oxford and AstraZeneca plan to publish study data, the paper added.
The European Union signed a new contract this month for 1.8 billion doses of the Pfizer-BioNTech vaccine to cover booster doses.