Molecular Evolution Of Rubella Viruses Circulated In The Mainland Of China And Its Antigenic Difference With Chinese Rubella Vaccine

Rubella is an acute respiratory infectious disease caused by rubella virus (RV) infection, and the most serious disease caused by RV is congenital rubella syndrome (CRS). Rubella is a vaccine preventable disease; hence, the only effective measure against rubella and CRS is vaccination with rubella containing vaccine (RCV). In 2008, China began to introduce rubella vaccine into the national expand immunization program, and routine vaccination was implemented for children. The aim of this study was to elucidate the genetic characterization, the trend of transmission of RV after the prevalence of rubella in 2008 and after rubella vaccine was included in the national immunization program; on this basis, to investigate molecular evolution characteristics and the dynamic change rule of variation of RV; meanwhile, to clarify the influence of the evolution of RV on the protective effect of rubella vaccine.In this study, total 1580 viruses were collected in 29 of 31 provinces of mainland China during 2008-2015. Through the genotyping method, the results confirmed that rubella epidemic during this period time were caused by multiple transmission chains of genotype 1E and 2B virus. Then 202 representative RVs of genotype 1E and 2B between 2000 and 2015 were selected for the molecular evolution analysis. The results indicated that genotype 1E RV could be traced back to 1991 and were likely introduced into mainland China around 1997. After it's firstly detection in 2001, genotype 1E became the predominant genotype circulated during 2001-2013. Different from genotype 1E circulated in other countries and region, this genotype 1E was specific to China and could be divided into two closely related Clusters including Cluster A (2004-2015) and Cluster B (2001-2009), and Cluster A is now the predominant subgenotype circulating in China. However, the detection rate of 1E genotype RV decreased year by year during 2011-2015, and it reached the lowest level 1.3% (only 4 strains) in 2015. The earliest ancestors of genotype 2B RV could be traced back to 1962, and at least 4 different genotypes of 2B RV (Lineage 1-4) circulated in China since 2000, and among them, the circulation of 2B-Lineagel, Lineage2, and Lineage4 had been interrupted; it was speculated that the 2B-Lineage3 introduced into China around 2007, and after it was firstly detected in 2011, it was wildly spread from the eastern region to the western region in China, and became the predominant genotype instead of genotype 1E RVs during 2014-2015. The estimated evolutionary rate of genotype 2B RV (2.0×10-3 nucleotide substitution/year) is slightly faster than the rate of genotype 1E RV (1.56×10-3 nucleotide substitution/year), but still slightly slower than some of the other RNA viruses, which may be related to the highly conserved nucleotide and amino acid of the viruses.According to the geography and age distribution, eight genotype 1E RVs and three genotype 2B RVs were selected for whole genomic sequences determination. Through comparative genomics research, the results showed that most of the nucleotide variation of genotype 1E and 2B RVs are transition and the mutations appeared frequently in the third codon position. The amino acids of known important functional areas are highly conserved. The above results indicated that, the epidemic range of genotype 1E RVs decreases has nothing to do with the evolution of the viruses, but the effective implementation of rubella vaccine immunization strategy, which rapidly increase the population immunity, eliminate a certain number of susceptible populations, effectively interrupt the transmission chains of viruses, and maintain the incidence of rubella at a low level.In order to clarify the influence of the evolution of RV on the protective effect of rubella vaccine (BRDII strain), the antigenic difference between Chinese indigenous RV strains and rubella vaccine strain (BRDII) was studied based on the whole genome sequences and the cellular level. The preliminary results indicated that the vaccine strains (BRDII) and the wild RV strains prevalent in China can be cross protected, and the difference of amino acid sites between Chinese RV strains and BRDII vaccine strain did not cause significant antigenic changes. Hence, these findings suggested that rubella vaccine currently used could effectively protect the population from rubella virus infection.In conclusion, based on this study on the etiology of RV circulated in China for 16 consecutive years, the prevalence rule of RV in China is expounded from the molecular level, and the evolution and epidemic situation is mastered; The understanding of the genetic characteristics, genotyping, and the law of genetic evolution was improved; The viral strain bank and gene database of Chinese indigenous RV strains were established. On this basis, the antigenic difference between Chinese indigenous RV strains and rubella vaccine strain (BRDII) was researched based on the whole genome sequences and the cellular level, and the basic data of the cross protection effect between them were acquired. This study makes an important contribution to enrich global rubella virus strains bank and gene library, meanwhile, it provides important virological monitoring data for the rubella control and the future elimination in China, provides scientific data for the further perfection of rubella vaccine immunization strategy, and also provides scientific support for the prevention and control measures of rubella and CRS.