FRANKFURT: Pfizer's German development partner BioNTech on Thursday joined other leading COVID-19 vaccine developers in ruling out participation in British plans to test experimental inoculations by deliberately infecting trial volunteers.

"BioNTech's vaccine candidate is not part of this study," a spokeswoman said.

Britain is planning to host so-called "challenge trials", the Financial Times cited people involved in the project as saying.

Britain said it was working with partners on the potential for human challenge trials without commenting on a specific plan.

AstraZeneca and Sanofi both have said their vaccine candidates were not involved in the programme.