Jimmy Fallon is giving a boost to COVID-19 vaccine boosters, teaming up with Ariana Grande and Megan Thee Stallion for an offbeat, Christmas-themed music video encouraging Americans to get "in line" for the shots. "It was a masked Christmas, we stayed in the house. We covered our nose, and covered our mouth," the NBC "Tonight Show" host croons in "It Was a (Masked Christmas)," which he debuted on Monday. "But it's Christmas time, we’ll be in line for a booster." Other lines in the tune include: "This Christmas Imma make it count, no more quarantine on the couch. This year...