The anti-vaccination movement is a loosely-organized conspiracy-theorist subculture that blames the medical practice of vaccination for a wide range of health problems and whose advocates have, ironically, been directly responsible for the return of health disasters by reinvigorating diseases that had almost been eradicated by said vaccines. The movement, largely led by people with no medical or scientific qualifications (or, tellingly, stripped of credentials for malpractice and fraud), bases its claims largely on spurious alleged short- and long-term side-effects of vaccinations. Effects which are — to boot — often trivial when compared to the severity of what were once common illnesses.
Anti-vaccination proponents argue that vaccines are deadly poisons (and that this ought to be "considered completely proven" to anyone but a shill). Yet the anti-vaccination movement fails to gain traction outside of social media. Therefore, by necessity, they argue that some kind of cover-up must be taking place (particularly in the CDC), that the vaccines serve an agenda completely different from disease prevention, or that the anti-vaccination "whistleblowers" are being kept down by some sort of shadowy power.