Molecular Epidemiology, Transmission, and Evolution of Rubella Virus Circulating in Tianjin, China, Between 2009 and 2020.

Rubella is listed as a disease that needs to be eliminated worldwide by the World Health Organization. This study aimed to investigate rubella epidemiology and genetic characteristics based on data from 12 years of laboratory-based surveillance (2009-2020) in Tianjin and to provide baseline genotype data for monitoring future rubella control efforts. We collected RV-positive throat swab samples from confirmed rubella cases during 2009-2020 in Tianjin to isolate RV, amplify and sequence target gene fragments, construct phylogenetic trees, and analyze nucleotide homologies. Four rubella isolates were chosen for whole genome sequencing. The epidemiological data of rubella cases were collected to describe and analyze the epidemiological characteristics of the rubella outbreak. Most cases (87.6%) occurred between March and June, and the peak incidence was observed in May. The age of the reported rubella cases ranged from almost 1 month to 82 years, most were between 10 and 29 years old (83.3%). Almost half (48.3%) of the confirmed rubella cases were from just four districts (Beichen District, Binhai New Area, Hebei District, and Nankai District). A total of 211 rubella virus strains were obtained during 2009-2020, phylogenetic analyses identified four lineages, including 1E-L1, 1E-L2, 2B-L1, and 2B-L2c, with high homologies of nucleotide sequences compared with RV strains from other provinces of China. Recombination analysis indicated that strain RVi/Tianjin.CHN/37.19/1 a possible recombination strain by 7 analysis methods, with p-values of 4.993 × 10-2.922 × 10. Our study provided comprehensive data on rubella epidemiology and the first information on rubella genotypes in Tianjin. Clear evidence of recombination was found, indicating that RV has the potential to continually mutate, so close monitoring of the genetic variations of wild-type rubella virus strains is necessary. Rubella viruses were highly conserved at the genomic level, the incidence of rubella in Tianjin, as well as in China, has sustains at a low level, which gives us the idea that the rubella control and elimination goal could be achieved in the near future if strengthened RV surveillance continues and vaccine immunization coverage maintaining at the high level.