Measles incidence rate and a phylogenetic study of contemporary genotype H1 measles strains in China: is an improved measles vaccine needed?

The incidence of measles in China has increased over the last decade. To evaluate the genetic variation of measles strains, 16 measles wild-type virus strains were isolated from 14 vaccinated cases and 2 nonvaccinated cases in Jilin Province during 2005-2006, and their nucleoprotein (N) and hemagglutinin (H) genes were amplified by RT-PCR. The amplified products were sequenced and compared with the Edmonston virus and the existing vaccine strains (Changchun-47 and Shanghai-191). The results showed that the variation rate between the vaccine and wild-type strains was 9.8-12.0% in the N gene and 5.9-6.9% in the H gene, respectively. In addition, cross-neutralization assays revealed that although sera obtained from infants following primary vaccination effectively neutralized vaccine strains, the capacity in neutralizing H1 wild-type measles virus isolates was decreased fourfold. Antigenic ratios testing revealed that the antigenic relatedness between wild-type measles viruses and existing vaccine strains was notably low. These data suggest that the increased incidence of measles in Jilin Province may be attributed to the antigenic drift between wild-type and vaccine strains. Our findings strengthen the recommendation of supplemental immunization with existing vaccines and also strongly suggest a need for developing new vaccines to better control measles virus outbreaks.