BBC News
By Michelle Roberts
Published
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image captionOver-50s who have had a dose of the Pfizer or AstraZeneca vaccine can take part in a study on mixing jabs
A major UK trial looking at whether Covid vaccines can be mixed with different types of jabs used for first and second doses is being expanded.
Combining vaccines might give broader, longer-lasting immunity against the virus and new variants of it, and offer more flexibility to vaccine rollout.
Adults over 50 who have had a first dose of Pfizer or AstraZeneca can apply to take part in the Com-Cov study.