British scientists are starting a study to find out if it's okay to mix and match Covid-19 vaccines, according to AP.

The vaccines being rolled out now require two doses, and people are supposed to get two shots of the same kind, weeks apart. Guidelines in Britain and the US say the vaccines aren't interchangeable, but can be mixed if the same kind isn't available for the second dose or if its not known what was given for the first shot.

Participants in the government-funded study will get one shot of the AstraZeneca vaccine followed by a dose from Pfizer, or vice versa.

"This study will give us greater insight into how we can use vaccines to stay on top of this nasty disease," said Jonathan Van Tam, the UK's deputy chief medical officer.