ing. A recent study of various commercial mumps vaccine preparations demonstrates the existence of two populations of Jeryl Lynn strain virus in commercial vaccine preparations, with sequence variation of up to 4.4 percent for some genes (Afzal et al., 1992). Only one population of the Urabe strain was detected. The authors hypothesized that one of the populations could interfere with the growth of the other, thus influencing rates of adverse reactions. There are no data to substantiate this hypothesis directly.

Conclusion

The evidence is inadequate to accept or reject a causal relation between the Jeryl Lynn strain mumps vaccine and aseptic meningitis.

SUBACUTE SCLEROSING PANENCEPHALITIS

Clinical Description

Subacute sclerosing panencephalitis (SSPE) is a rare subacute encephalitis accompanied by demyelination. The entire course of SSPE may be one of slow progressive deterioration, but variable periods of remission can occur. The usual duration is about 12 to 24 months to a vegetative state or death. A more complete discussion of SSPE can be found in Chapter 3.

History of Suspected Association

Laboratory findings implicate a measles-like virus as the cause of SSPE. Epidemiologic data have also linked SSPE to prior measles infection.

The first report of SSPE in a patient with a negative history for measles but a positive history of vaccination with live attenuated measles vaccine was reported in 1968 (Schneck, 1968). The child had received measles vaccine with immune globulin 3 weeks prior to the onset of symptoms. The clinical course accelerated 10 weeks after vaccination, and the child died 18 months after vaccination. Serologic studies were not performed, but postmortem histologic examination of the brain supported a diagnosis of SSPE. Several more case reports of SSPE in children negative by history for measles but positive for receipt of the measles vaccine followed and are described in more detail below.

The dramatic decline in the number of measles cases in the United States from 1964 to 1968 paralleled a decline in the number of cases of SSPE starting in the early 1970's. Only 4.2 new cases of SSPE per year, on average, were reported from 1982 to 1986 (Dyken et al., 1989). This is in contrast to the 48.6 new cases of SSPE per year, on average, reported from 1967 to 1971. This decline is attributed to the increased use of measles



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