A UK trial has been launched to see if giving people different Covid vaccines for their first and second doses works as well as the current approach of using the same type of vaccine twice.
The idea is to provide more flexibility with vaccine rollout and help deal with any potential disruption to supplies.
And scientists say it is possible the new approach could even provide better protection than giving the same jabs.
For those not taking part in the trial, the regimen remains unchanged.
Currently, official guidance from the Joint Committee on Vaccination and Immunisation (JCVI) says anyone already given the Pfizer-BioNTech or Oxford-AstraZeneca jab as part of the UK’s approved immunisation programme should get the same vaccine for both doses.
In very rare circumstances a different vaccine can be used – if only one vaccine is available, or it’s not known which was given for the first dose.
Scientists have good reason to believe the new mixing approach being trialled may prove beneficial – some Ebola immunisation programmes involve mixing different jabs to improve protection, for example.
The Com-Cov study, run by the National Immunisation Schedule Evaluation Consortium, will involve more than 800 volunteers over the age of 50 in England.
Some will receive the Oxford-AstraZeneca jab followed by the Pfizer-BioNTech vaccine or vice versa – four or 12 weeks apart.
Other vaccines may be added as they are approved by regulators.