Postvaccination encephalopathy
The possible role of vaccination (particularly pertussis vaccination) in causing a childhood encephalopathy and subsequent epilepsy and learning disability has been the subject of intense study, with contradictory claims. The UK National Childhood Encephalopathy Study found that children hospitalized with seizures and encephalopathy were more likely to have received diphtheria-tetanus-pertussis (DTP) vaccination in the previous 7 days than control children. However, the potential methodological bias of this study has been severely criticized. A more recent large series of 368,000 children after immunization found no difference in rates of epilepsy when compared with controls. Similarly, suggestions that mumps-measles-rubella (MMR) vaccine increases the risks of autism and epilepsy are now thought to be unfounded. Most vaccines are now not prepared from infected live neural tissue and as a result there has been a significant reduction in post-vaccination encephalomyelitits. Conventional medical advice is now that vaccination is safe, and although a small number of children do develop encephalopathic reactions which result in later epilepsy, the risk of this occurring is considerably less than the risk of encephalopathy after the naturally occurring viral illnesses that vaccination prevents. Thus, for instance, the generally accepted rate of post-vaccination encephalomyelitis following measles vaccination is about 1-2 per million, compared with the risk of post-measles encephalomyelitis of about 1-2 per 1000. Currently, the vaccine with the greatest risk is the smallpox vaccine, with a rate of 10-300 cases per million of post-vaccination encephalomyelitis, although safer vaccines are under development. The vaccines known to be associated with postvaccination encephalomyelitis are smallpox, measles, DTP, Japanese B encephalitis, and rabies.
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