Simian virus 40 in polio vaccine: follow-up of newborn recipients.

Soon after birth, when susceptibility to carcinogens should be enhanced, a group of children received oral polio vaccine which was later found to contain significant amounts of simian virus 40. Eight years after the incident, no cancer deaths have been observed among the vaccinated children, but continued surveillance is needed before concluding that simian virus 40 is innocuous to man.