Vaccinations pose only a small risk of causing fever-related seizures in babies and the benefits of the shots far outweigh any risks, a study has found.
Even when seizures occur, the effect is only temporary, the New England Journal of Medicine reports.
Dr William E. Barlow, of the Centre for Health Studiesin Seattle, and his fellow researchers collected data from four large health maintenance organisations which treat about one in 40 American children under the age of 7 to see how many had seizures after being vaccinated.
Compared with children who were not recently vaccinated, the researchers found that of 680,000 children in the study, fewer than 1 in 13,000 protected against diphtheria, tetanus and whooping cough by the DTP vaccine had a seizure.
The seizure rate was less than 1 in 3300 for children who received the MMR vaccine for measles, mumps and rubella.
The seizures associated with the MMR vaccinations tended to occur eight to 14 days after vaccination; the DTP shot was most likely to spark a seizure on the day of the vaccination.
(An even safer version of the DTP vaccine has since come into widespread use.)
When they followed the cases of children who had a seizure, the Barlow team found that the risk of having learning or developmental disabilities "did not differ between children who had been exposed and those who had not been exposed" to the vaccines at the time of their seizure.
As well, they concluded, children who had a seizure after a vaccination did not face a greater risk of having future seizures, or of being diagnosed with epilepsy.
"A child's fever-related seizure did not result in any lasting adverse consequences for the child," Dr Barlow said.
The benefits of the shots outweighed the risks. For example, unvaccinated children risk neurological problems if they develop measles or whooping cough.
The MMR vaccine is usually given at age 12 months to 15 months, with a booster between the ages of 4 and 6. At the times of the study, the DTP vaccine was given in five doses from ages two months to six years.
