But “in exceptional situations in which the first-dose vaccine product cannot be determined or is no longer available,” the guidelines added, any available mRNA vaccine can be used for the second dose. But if that is “not feasible,” the agency wrote, the interval between doses may be extended to six weeks. has warned that one variant, which is believed to be 50 percent more contagious, might become the dominant source of infection in the United States by March. And the current vaccination effort, which had little central direction under the Trump administration, has so far sown confusion and frustration. Some localities are complaining they are running out of doses, while others have unused vials sitting on shelves.

Source: New York Times January 22, 2021 23:30 UTC