I’ve noticed that British news stories concerning COVID-19 vaccinations generally refer to such shots as “jabs.” Until very recently, I had never encountered this term’s being used by American reporters.Merriam-Webster offers this definition of the noun “jab”:
Cambridge Dictionary offers a similar definition:
chiefly British, informal: an injection of something (such as medicine) into one’s body with a needle
UK informal: an injection
The use of “jab” for “vaccination” seems un-American. I hope this is a usage that does not catch on. Being a single-syllable word, “jab” is “efficient”—“vaccination” is four syllables—but it is actually non-specific, its exact meaning only clear from context.