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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality
authors provided no clinical information other than the fact that she recovered completely.
Several small case series described in the literature looked for adverse events following immunization with both DPT and DT (Feery, 1982; Waight et al., 1983). Those studies showed no adverse neurologic events following receipt of DT, although the sample sizes in those two studies were small (335 and 221 subjects, respectively).
The following cases were reported in the Vaccine Adverse Event Reporting System (VAERS) between November 1990 and July 1992: a 50-year-old male who developed syncope, visual disturbance, and hypoglycemia 1 day after receiving tetanus toxoid; a 14-year-old male who developed encephalitis and transverse myelitis 2.5 months following Td administration; and a 17-year-old male who developed lymphocytic meningoencephalitis 10 days following receipt of Td and measles-mumps-rubella vaccine (MMR).
Controlled Observational Studies
The best observational case-control study that provides information about immunization with DT and association with neurologic illness is the National Childhood Encephalopathy Study (NCES) (Alderslade et al., 1981), which was undertaken because of concerns about possible adverse events following receipt of pertussis vaccine. That study identified children aged 2-36 months who were admitted to a hospital with neurologic illness during the 3 years from July 1976 to June 1979 in England, Scotland, and Wales. The first 1,000 of 1,182 cases identified during that time were studied. For each case there were two ''at-home'' controls matched for age, sex, and area of residence. No statistically significant association with DT immunization and neurologic adverse events was found in cases compared with controls. On the basis of the data in Table V.15 on page 122 of the NCES (Alderslade et al., 1981), the odds ratio (OR) is 0.92 (95 percent confidence interval [CI], 0.64-1.30). However, as with infantile spasms, a nonsignificantly higher rate of exposure to DT was observed within the 7 days prior to the date of onset of illness in the case patients, and a correspondingly lower rate of exposure was observed between more than 7 and less than 28 days prior to onset. Because nearly one-third of the cases had prolonged febrile convulsions, the excess rate of exposure to DT within 7 days, if real, may merely reflect the tendency of DT vaccination to cause fever.
Greco (1985) carried out a case-control study in the Campania (Naples) region of Italy from January 1980 to February 1983 to test the association between encephalopathy and immunization with DT. The Italian Ministry of Health had received reports that described several cases of encephalopathy in children who had received DT within the week prior to illness, and those reports were the impetus for the study. A case was defined as a patient