The story
From a Twitter post by Donald Trump (@realDonaldTrump) in 2014, popularized during his campaign for President of the United States in 2016: Healthy young child goes to doctor, gets pumped with massive shot of many vaccines, doesn't feel good and changes - AUTISM. Many such cases! The phrase itself has been rarely attested in literature, from at least the 19th century, primarily in medical or legal context. Endured primarily on the Internet, especially in 4chan slang.
Etymology from Wiktionary, CC BY-SA 4.0.