Causality Argument

There is no evidence bearing on a causal relation between measles vaccine and orchitis or sterility.

Biologic plausibility for a causal relation between mumps vaccine and orchitis stems from the relation between wild-type mumps virus and orchitis (Association for the Study of Infectious Disease, 1974; Bendersky-Malbec, 1982; British Medical Journal, 1980; Sandler, 1954; Werner, 1950a,b) and from the temporal correlation between mumps vaccine and orchitis in several individual cases. Because orchitis is uncommon, it seems possible that cases temporally related to mumps vaccination are caused by the vaccine virus. However, it is also possible that at least some of the cases of orchitis following administration of mumps vaccine were caused by infection with wild-type virus, because the impetus to immunize males often is exposure to mumps disease. It should be noted that even though millions of doses of mumps vaccine have been administered, very few cases of mumps vaccine-associated orchitis have been reported.

There are no case reports of sterility in the literature or in VAERS (submitted between November 1990 and July 1992). However, these data are difficult to obtain because of the number of years required for follow-up. Because there are case reports of bilateral orchitis following administration of mumps vaccine, there is a possibility of sterility, and thus, a causal relation between mumps vaccine and sterility has not been fully studied.

Conclusion

There is no evidence bearing on a causal relation between measles vaccine and orchitis or sterility.

The available evidence is inadequate to accept or reject a causal relation between mumps vaccine and orchitis.

The available evidence is inadequate to accept or reject a causal relation between mumps vaccine and sterility.

THROMBOCYTOPENIA

Clinical Description

Thrombocytopenia is a decrease in the number of platelets, the cells involved in blood clotting. Thrombocytopenia may stem from the failure of platelet production, a shortened platelet life span, or an abnormal distribution of platelets within the body (Lee et al., 1993). Normal platelet counts are on the order of 150,000 to 450,000/mm3. Thrombocytopenia occurs in



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