An IOM study committee on adverse events associated with vaccines found that evidence was inadequate to accept or reject the claim that transverse myelitis was associated with OPV (IOM, 1994). The committee found that there was evidence favoring acceptance of a causal relationship with Guillain-Barré syndrome. However, this association has been brought into question with subsequent publication of data on the episode that the committee cited. The committee also found that the evidence established a causal relation between OPV and paralytic and nonparalytic polio.

With the exception of earlier findings of simian virus 40 (SV40) contamination in OPV and IPV vaccine prepared from monkey kidneys, there has been no conclusive evidence of other adventitious agents in OPV. Adverse effects of that contamination have not been documented, but it is possible that follow-up might not have been sufficiently long-term or comprehensive to detect them. Other research describing the extraction from human tissue of genetic material resembling SV40 (Carbone et al., 1994) or with significant homology to an African green monkey cytomegalovirus isolate (Martin et al., 1995) has led the authors to speculate that the source of this material might be viral vaccines. Since the time of the SV40 episode, vaccine has been prepared in the kidneys of monkeys born in colonies where adventitious agents are screened out rather than from monkeys caught in the wild. The screening for adventitious agents, including retroviruses, by both manufacturers and FDA, is rigorous. Safety testing is not only for adventitious agents but also for neurovirulent poliovirus.


Vaccine Characteristics

Two IPV products are currently licensed in the United States. Both are known as enhanced-potency IPVs because they contain higher amounts of antigen than the IPV originally licensed in the 1950s. The manufacturing methods and sources of these two vaccines differ, with one produced on Vero cells manufactured in France and the other grown on MRC-5 cells (a human diploid cell line) manufactured in Canada. The vaccine is obtained from supernatants of cell cultures that are filtrated and concentrated. Impurities are removed and the virus is inactivated with formalin. After 6 days of inactivation, at which time the virus is no longer viable, viral clumps are


The material in this section is adapted from presentations by Carlton Meschievitz and Stanley Plotkin and comments by other workshop speakers or participants.

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