The article that appeared online on Feb. 9 began with a seemingly innocuous question about the legal definition of vaccines. Then over its next 3,400 words, it declared coronavirus vaccines were “a medical fraud” and said the injections did not prevent infections, provide immunity or stop transmission of the disease.

Instead, the article claimed, the shots “alter your genetic coding, turning you into a viral protein factory that has no off-switch.”

Its assertions were easily disprovable. No matter. Over the next few hours, the article was translated from English into Spanish and Polish....