evidence: Misleading: The claim that the MMR vaccine causes encephalopathy is based on a misinterpretation of the vaccine package insert information. FULL CLAIM: Toxic vaccine ingredients in the MMR vaccine cause encephalopathy In this popular Facebook video, shared more than 300,000 times and viewed more than 18 million times, Del Bigtree claims firstly that vaccines contain several toxic ingredients and that these are the reason for encephalopathy, which he calls a "known side effect of every vaccine we get". The specific ingredients he calls out are mercury, aluminium, propylene glycol and formaldehyde. Secondly, he claims that the safety of vaccines is unknown.