Pertussis vaccine is sometimes blamed for causing brain damage in infants and young children. A review of all of the scientific evidence carried out by the Institute of Medicine in the United States found that there is no proof that pertussis vaccine causes brain damage. Four American studies involving over 415,000 children who received nearly one million doses of pertussis vaccine failed to find a single case of acute illness involving the brain, other than convulsions. Such convulsions do not cause permanent damage. A study in the United Kingdom was also unable to find a single case of permanent brain damage that was clearly the result of vaccination. If brain damage does occur after vaccination, it is extremely rare. Why then, has pertussis vaccine been blamed for causing brain damage? Vaccination is a very common and recognizable event in the first six months of life of most infants. Brain abnormalities, on the other hand, are uncommon and often unrecognizable in the first six months of life. Most infants who have malformations of the brain or who suffer brain damage before birth or during labour and delivery appear to be normal for the first few months of life because the brain is not fully developed. Many babies are 4 to 6 months of age or more before it becomes clear that something is wrong with their development. The diagnosis of cerebral palsy, mental retardation or developmental delay can usually not be made until the infant is several months old. By this time, the baby has already received one or more vaccinations, often with minor side effects such as fever, crying and fussiness. Since the infant appeared to be normal until the vaccine was given, the vaccine is blamed. The following facts make it extremely unlikely that pertussis vaccine can cause brain damage: acute illness involving the brain has not been shown to be more common after vaccination than at any other time (except for febrile or fever-induced convulsions, which do not cause brain damage); studies of large numbers of children have found that brain damage after vaccination is very rare, if it occurs at all; in searching for a link between brain damage and pertussis vaccine, no pattern of symptoms or abnormalities of laboratory tests have been found, and upon examination of the brain after death, no findings have been described that would establish pertussis vaccine as the cause of brain trauma; the damage in the brains of children who die of natural pertussis is caused by lack of oxygen and bleeding from small blood vessels as a result of severe coughing spells, not as a result of a toxin from the bacteria; no plausible mechanism has been found by which pertussis vaccination could cause brain damage.

This document was published by the Canadian Paediatric society, 1997.

Posted by the Canadian Paediatric Society, July 1997.

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