The World Health Organization revealed on Tuesday that under “exceptional circumstances,” the second dose of the BioNTech/Pfizer coronavirus vaccine can be inoculated up to six weeks after the first shot.

The statement comes as Britain is considering delaying the second shot of the vaccine in order to cover maximum people with the first dose so as to provide some form of protection against Covid-19, Politico reported.

Briefing press, Alejandro Cravioto, of the WHO’s Strategic Advisory Group of Experts on Immunization (SAGE), said that the SAGE’s official recommendation is for the BioNTech/Pfizer vaccine doses to be given within 21 to 28 days.

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However, they have “made a provision for countries in exceptional circumstances of vaccine supply constraints and epidemiological settings to delay the administration of the second dose for a few weeks in order to maximize the number of individuals benefiting from a first dose.”

But unlike the U.K. decision to allow up to 12 weeks between the first and second dose, the WHO’s SAGE allows an interval of only six weeks.