evidence: Presumably, the vaccine lots that have been suspected of causing irreversible encephalopathy in children have passed the intracerebral mouse protection test or the intranasal mouse protection test for vaccine potency and the mouse weight gain test for toxicity. Therefore, the capacity to cause serious encephalopathy in mice, if present, has been missed. The endpoint of the intracerebral mouse protection test is death from active infection within 14 days. The interval between injection of vaccine and intracerebral injection of viable organisms, a matter of a few weeks, might not be sufficient for detection of late neurologic effects. More importantly, neurologic sequelae that might relate to changes in memory, learning ability, emotional control, and the like might not be obvious in mice. Similar considerations apply to the mouse weight gain test, which is carried out for up to 7 days and which focuses on weight gain as an endpoint. In summary, it is not evident that the studies in animals completed to date provide information useful to understanding the possible relation of encephalopathy to pertussis immunization in children. The possibility has been raised that the aluminum salts regularly present in DPT vaccines might play a role in the occurrence of encephalopathy following DPT immunization (see Appendix E for discussion). There are no data bearing on this possible mechanism. [...] Griffin MR, Ray WA, Mortimer EA, Fenichel GM, Schaffner W. 1990. Risk of seizures and encephalopathy after immunization with the diphtheria-tetanus-pertussis vaccine. Journal of the American Medical Association 263:1641-1645. [PubMed: 2308203]