COMMENTARY: Is Japan Deaf to Mumps Vaccination?

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In this issue of the Pediatric Infectious Disease Journal, Hashimoto et al1 show that mumps in Japan is accompanied by sudden deafness. To physicians in countries that use MMR vaccine, this will come as a surprise only to those too young to have seen mumps before the introduction of vaccination. Indeed, even those physicians in the United States and Europe who recently have seen mumps in some previously vaccinated adolescents may be misled by the benignity of the modified illness.
Mumps vaccines are not regularly used in Japan, and the article by Hashimoto et al documents an incidence of deafness following mumps equivalent to 1 per 1000 cases, significantly larger than heretofore documented. The peak number of cases occurred at age 4 years. Other complications, such as aseptic meningitis, which has a reported incidence as high as 0.5% to 15% of cases,2 were not studied.
However, aside from confirmation of the seriousness of mumps, the article carries another important message: the lack of universal mumps vaccination in Japan. The circumstances surrounding this situation are interesting. Many mumps strains have been developed as attenuated vaccines throughout the world. Unfortunately, all except the Jeryl Lynn strain and its derivatives are capable of causing aseptic meningitis.3 The reported rates of meningitis differ among the various strains and even for the same strain in different studies, with those used in Japan having rates as high as 1 per 1000 vaccinations.4 Some strains used outside Japan have similar rates, but other strains have much lower rates of aseptic meningitis (<1/10,000 doses) and are considered to have a favorable risk/benefit ratio that merits their use.5
It may seem unusual, but the Japanese authorities have failed to allow licensure and importation of MMR vaccines containing the Jeryl Lynn strain, and one can only presume that this is due to protectionism in favor of indigenous manufacturers. The absence of prophylactic vaccination against mumps is surprising for a developed country, and this regrettable policy must be changed for the sake of Japanese children.

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