Coulter's book, DTP: A Shot in the Dark, co-authored with Barbara Loe Fisher (first published in 1985 and reprinted several times since), features interviews with 100 families where the parents suspected vaccine damage: "We found a very high incidence of seizure disorders," he says.Vaccination causes a slight degree of encephalitis in children. Doctors recognize this happens but insist it occurs only once in every 100,000 cases: "In my opinion, it happens about once in five," says Coulter. "When you have encephalitis, the child may recover completely, but it may not and may suffer some long-term damage." One of the most common after effects of seizures is epilepsy.

"It's generally recognized by doctors from both sides of the Atlantic that vaccination causes a type of encephalitis. That's a very important point," he says and cites a 1983 British study which supports Coulter's earlier research (The National Childhood Encephalopathy Study-NCES): "This is the best study that has been done on vaccination reactions, and it found a connection between the pertussis (whooping cough) vaccine and acute reactions occurring within seven days."

Ten years later, a follow-up report was published: Immunization and Acute Neurological Illnesses in Children (BMJ, 1993; 307:1171-6), concluded that children who suffered an acute reaction from the whooping cough vaccine suffered from a permanent neurological disability later in life.

Encephalitis can be caused by a number of different things. In particular, Coulter discovered there had been an epidemic of encephalitis in the 1920s and 30s, which affected 20 to 30 million people worldwide. It accounted for a couple of million deaths, with an equivalent number of survivors suffering from serious disabilities: "I found out that the types of consequences after an epidemic of encephalitis were identical with what we call today "minimal brain damage", "seizure disorders", asthma, allergies, and so on," he says.