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.