“WHO’s recommendation at present is that the interval between doses may be extended up to 42 days (6 weeks), on the basis of currently available clinical trial data,” it said, adding: “Should additional data become available on longer intervals between doses, revision of this recommendation will be considered.”

Hard-hit Britain, for example, has decided to delay for as much as 12 weeks — and data from that expansion could help contribute to possible revisions in the WHO recommendation, said WHO spokeswoman Dr. Margaret Harris.