BioNTech and partner Pfizer warned on Monday that they had no evidence that their jointly developed vaccine will continue to protect against Covid-19 if the booster shot is given later than tested in trials.
"The safety and efficacy of the vaccine has not been evaluated on different dosing schedules as the majority of trial participants received the second dose within the window specified in the study design," the companies said in a joint statement, referring to prime and a booster shots given three weeks apart.
"There is no data to demonstrate that protection after the first dose is sustained after 21 days."
Germany was considering on Monday whether to allow a delay in administering the second dose to make scarce supplies go further after a similar move by Britain last week. Separately, Denmark approved a delay of up to six weeks between the first and second shots of the vaccine.