A major UK trial looking at whether Covid vaccines can be mixed is recruiting adults over 50 who have had a first dose of Pfizer or AstraZeneca to take part.

Axar.az reports that the participants' second dose could be the same again, or a shot of Moderna or Novavax.

Prof Matthew Snape, chief investigator, tells BBC Radio 4's Today programme the volunteers will not know which jab they are getting in the randomised trial.

The study will look for reactions and will test immune responses, he says, adding that there are "some hints from studies in mice that a combination of vaccines might give a better response overall".