the speaker, genetic studies suggest that their illness is caused by a newly identified cytomegalovirus closely related to a type that infects African green monkeys. Although there is no evidence of the possible source of the genetic material identified, because the kidney cells of these monkeys are used to culture the viral strains used in the live-virus polio virus vaccine, the speaker hypothesized that at least some lots of this vaccine might harbor a strain of cytomegalovirus that can cause severe brain deterioration decades after vaccination. Although the monkey kidney cells currently used in oral polio virus vaccine production come from laboratory monkeys that are not thought to be infected with viruses and that are screened for viral contamination, previously unsuspected (and therefore not screened for) viruses or viruses present at very low levels could theoretically contaminate the vaccine. A consumer organization representative suggested that FDA regulations for vaccine safety be reviewed and updated to reflect the state of the art in scientific technology so that vaccines are more thoroughly tested for adventitious agents. This testing should include evaluations of the possible roles of additives such as aluminum and formaldehyde in adverse events.

A CDC representative noted that a large number of possible long-term adverse effects could be considered. Given the limited resources at hand, he suggested limiting studies to those effects that seem to be biologically plausible. According to workshop participants, these findings reinforce the need for long-term studies to determine late-onset adverse effects of vaccines. They also suggest that newly devised laboratory tools for virus detection such as the polymerase chain reaction should perhaps be applied even to those vaccines that have historically been accepted as safe to detect adventitious viruses that might cause long-term adverse effects. Such research findings might help to narrow the search for the long-term adverse effects of vaccines.

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