H1 genotype of measles virus was detected in outbreaks in Japan after 2000

We investigated the molecular epidemiology and biological characteristics of wild measles viruses isolated since 1984 in Japan. The circulating measles virus was of genotype C1 before 1985, D3 from 1987 to 1990, and D5 from 1990 to 1997. It was replaced by the same cluster of Chicago-type D3 strain from 1997 to 1999. In 2000, D5 recirculated with sporadic cases caused by genotype H1. The H1 genotype became dominant in 2001 with a minor distribution of D5. No significant difference was observed in neutralizing titers against C1, D3, D5, and H1 when we used sera having high neutralizing titers. However, some D3 and H1 strains were not completely neutralized with low levels of neutralizing antibody, and maintaining high levels of measles antibodies would be required for the control measles outbreaks.