DIPHTHERIA AND TETANUS TOXOIDS DATA SUGGEST NO CAUSAL RELATION TO ADRs

DIPHTHERIA AND TETANUS TOXOIDS DATA SUGGEST NO CAUSAL RELATION TO ADRs, the Institute of Medicine's Vaccine Safety Committee concluded in a report released Sept. 14. The IoM committee found no evidence to link childhood immunizations with diphtheria and tetanus toxoids (DT) to encephalopathy, infantile spasms and death from sudden infant death syndrome (SIDS). The committee also found that the evidence favors rejection of a possible connection between conjugate Haemophilus influenzae type b vaccines and early onset of Hib disease. The IoM report, "Adverse Events Associate with Childhood Vaccines," was mandated by Congress in the 1986 National Childhood Vaccine Injury Act and is the second of two IoM reports prepared under the mandate. The first report, published in 1991, addressed the serious adverse effects of pertussis in diphtheria-pertussis- tetanus DTP and rubella vaccines ("The Pink Sheet" July 8, 1991, T&G-8). The first report found a causal relation between DPT and anaphylaxis, and inconsolable crying. The 14-member Vaccine Safety Committee that assembled the second report convened in early 1992 and was chaired by March of Dimes Birth Defects Foundation Medical Director Richard Johnston. Three case-control studies evaluated by the committee "offer no convincing evidence for the occurrence of encephalopathy following immunization with DT," the report states. The 1991 report found that DPT vaccination may be associated with acute encephalopathy. The new report adds, however, that "the possibility of lot-specific reactions to DT, as has been demonstrated for DPT preparations, suggests that studies could be more revealing if the vaccines were tracked by lot." The committee determined, as the previous committee had with DPT, that while infantile spasms have occurred in children receiving DT, the vaccine is not causally related to the adverse event. Similarly, the committee concluded that SIDS is probably not related to DT immunization although the syndrome does occur in populations of children receiving DT and DPT. The report states that "evidence favors acceptance of a causal relation between unconjugated PRP [I-Hib] vaccine and early-onset Hib disease," a serious systemic infection leading to meningitis or pneumonia within seven days of immunization, but that a causal relation between use of conjugated Hib vaccines and early-onset Hib disease is not likely. "Although these vaccines also appear to be capable of causing a transient decline in serum antibody levels following immunization, conjugate vaccines produce rapid and more predictable rise in protective antibody levels, and thus the interval of increased risk, if any is very short." The report does find evidence for a causal relation between: DT and anaphylaxis; measles vaccine and death from measles vaccine-strain viral infection; measles-mumps-rubella vaccine and thrombocytopenia and anaphylaxis; oral polio vaccine and poliomyelitis, and death from polio vaccine-strain viral infection; and hepatitis B vaccine and anaphylaxis. The IoM committee stressed that "most of the pathologic conditions our committee studied are rare in the general population and the risk of getting them from vaccines is extremely low." The report notes that "for the vast majority of vaccine- adverse event reactions studied, the data came predominantly from uncontrolled studies and case reports." While there are no definitive data, the report states that "the evidence favors acceptance of a causal relation" between: diphtheria and tetanus vaccines and Guillain-Barre syndrome (a nerve disease causing numbness and weakness of limbs) and brachial neuritis (weakness and marked atrophy of the arms); measles vaccine and anaphylaxis; oral polio vaccine and Guillain-Barre syndrome; and unconjugated Mb vaccine and Hib disease. In these cases, the committee said the evidence for a causal relation outweighs the evidence against. The committee found no evidence bearing on a causal relation between mumps vaccine and neuropathy or residual seizure disorder; or inactivated polio vaccine and transverse myelitis(spinal cord disease), thrombocytopenia and anaphylaxis. Because the IoM committee encountered a lack of data concerning vaccine adverse events in its review the report "encourages the consideration of a more active [surveillance] system" that would enable an increasingly energetic evaluation of possible adverse events after vaccination." Only one-third of the relations studied led to a conclusion accepting or rejecting the association of an adverse event with a particular vaccine. "For other relations the evidence was inadequate to accept or reject a causal relation or there was no evidence bearing on the relation," the report states. "Such a [surveillance] system might follow a representative sample of new vaccine recipients rather than the population at large," the report states. "Alternatively, a randomly selected subgroup of serious adverse events reported to VAERS [Centers for Disease Control and Prevention and FDA's Vaccine Adverse Event Reporting System] might be investigated fully." The committee found that while "large numbers of alleged adverse events are reported" to VAERS, "follow-up...was often incomplete, and the reported event was often not confirmed because of insufficient clinical, laboratory, or pathological data." Other suggestions proposed by the committee for the improvement of research and surveillance include the establishment of "regional or national disease registries" for rare conditions suspected of sometimes being caused by one or more licensed vaccines" (i.e., GBS, transverse myelitis or optic neuritis), and the employment of large databases to supplement passive surveillance reporting systems.