The prevention of mumps virus infection relies on the application of live, attenuated mumps virus vaccines. The process of attenuation from a wildtype mumps isolate to a safe vaccine has been empirical. A lower degree of attenuation results in solid immunity but carries an increased risk of post-vaccination meningitis due to the vaccine strain. Currently used vaccine strains are highly attenuated and essentially free of vaccine strain induced disease. However, their immunogenicity may be lower than previously reported.