The incidence of severe side effects is still not known, however, since they occur so rarely. Hundreds of thousands of children will have to be vaccinated before doctors can document these. In theory, the new vaccine should be much safer. Instead of being made like the old vaccine from whole pertussis bacterial cells that have been killed, the new acellular vaccine is made only from parts of pertussis bacteria that evoke protective immune responses. Although the new acellular vaccine is available, not all eligible children need it.
Many children tolerate the whole-cell vaccine just fine, and it is less expensive than the new one.
Parents should check with their children's doctor about which vaccine is right for them. In any case, children younger than 15 months should still be given the old vaccine unless their doctors recommend otherwise. It has some relatively minor adverse reactions, but the more severe reactions are still a matter of discussion. The American Academy of Pediatrics and pediatric societies in Canada and Great Britain have stated that the vaccine is not a proven cause of brain damage. And, while the risk of seizures from the whole-cell vaccine is about 1 in 1,750, numerous studies have shown there's no evidence those seizures will permanently harm the child or increase his or her chance of developing other seizure disorders, such as epilepsy, later.