Objective: To study the genetic variations between measles vaccine strain S191 and strains that circulated in Zhejiang province causing the epidemics during 1999 to 2011.
Methods: Complete sequence of the nine Zhejiang measles strains were amplified by RT-PCR assay. Products were sequenced and the obtained sequences were aligned and analyzed with vaccine strains S191 and the major epidemic strains isolated in foreign countries.
Results: The homology of amino acid among the nine Zhejiang strains were 98.77% - 99.89%. The strains were not affected by positive selection and the variations on each gene were still in random drift. Compared to vaccine strain S191, there were 135 to 159 amino acid changes in Zhejiang measles virus, in which 113 points were common variable positions, resulting in mutations on five glycosylation sites. At the nucleotide level, the biggest differences between the Zhejiang strains and the vaccine strain S191 were found on N gene, with the average divergent ratio as 5.5%, while the biggest one was P protein, in the amino acid level, with the average mutation rate as 7.7%. In addition, with the complete genome sequences, the genetic distance between Zhejiang epidemic strains and vaccine strains was greater than the distances between epidemic strains of genotype D(4), B(3) and vaccine strains (t = -9.76, P < 0.05; t = -12.39, P < 0.05).
Conclusion: There were significant differences found in the each of the genes between Zhejiang epidemic strains and the vaccine strain S191. The differences between the current vaccine strains and H genotype epidemic strains were much larger than the differences between the vaccine and the foreign epidemic strains (genotype D(4), B(3)). Therefore, we should pay close attention to this trend, and to develop candidates for the development of vaccines, as early as possible.