The European Medicines Agency is now recommending that a second dose of Pfizer's Covid-19 vaccine be given three weeks after the first, as many countries consider ways to stretch scarce supplies of shots.
The labelling of the vaccine, developed along with Germany's BioNTech and branded Comirnaty in Europe, before the latest change stated that the interval between the two doses should be "at least 21 days," the EMA said on Thursday.
Faced with a resurgence in infections and new, highly transmissible variants of the virus, some countries are hoping to broaden immunisation by giving some protection to as many people as possible with a first dose, and delaying subsequent doses.
The agency said the vaccine label would also include information that 93.1% of participants in the Pfizer-BioNTech trials received the second dose 19 to 23 days after the first dose.
The companies have warned they had no evidence their vaccine will continue to protect against Covid-19 if the booster shot is given later than tested in trials.
Britain, Mexico, and European countries such as Denmark, France, Germany and Netherlands have considered or implemented strategies to delay the second dose of Covid-19 vaccines. [Reuters]