There is demonstrated biologic plausibility that mumps vaccine could cause sensorineural deafness, in that wild-type mumps virus is associated with the condition. The biologic plausibility for a causal relation between measles vaccine and sensorineural deafness is less firm. Although cases of sensorineural deafness following administration of mumps and measles vaccines have been reported, the timing of onset and other nonspecific features make it impossible to distinguish vaccine from nonvaccine causation. Virus isolation would be helpful in assessing causality when the data are as scarce as described for the causal relation between measles and mumps vaccines and sensorineural deafness; however, such data are lacking.

The evidence is inadequate to accept or reject a causal relation between measles or mumps vaccines and sensorineural deafness.

Patients with optic neuritis present with unilateral or bilateral impairment of vision. This process can be transient, with full recovery following, or the loss of vision can be permanent. In most instances the underlying pathogenesis is demyelination involving the optic nerve. Chapter 3 contains a more detailed discussion of optic neuritis. No population-based incidence rates were identified.

Measles virus and measles vaccine have long been studied for their ability to cause demyelinating disorders. The committee was charged with investigating a possible causal relation between only measles vaccine and optic neuritis.

Chapter 3 contains a description of the general biologic plausibility for a role for vaccines, particularly live viral vaccines, in causing demyelinat-