Delayed peak of human infections and ongoing reassortment of H7N9 avian influenza virus in the newly affected western Chineses provinces during Wave Five

Eight additional provinces in western China reported human infections for the first time during the fifth wave of human H7N9 infections. Our study aimed to analyze the epidemiological and virological characteristics of this outbreak.
The epidemiological data of H7N9 cases from the newly affected western Chinese provinces were collected and analyzed. Meanwhile, full-length genome sequences of H7N9 virus were downloaded from GenBank and GISAID databases, and phylogenetic, genotyping and genetic analyses were conducted.
The peak of human infections in the newly affected western Chinese provinces was delayed by 4 months compared to the eastern China, and both low pathogenic (LP) and highly pathogenic (HP) H7N9 infected cases were found. The LP- and HP-H7N9 virus belonged to 10 different genotypes (including 4 new genotypes), of which G11 and G3 were the dominant genotypes, respectively. Almost all of these viruses originated from eastern and southern China, and were most possibly imported from neighboring provinces. Genetic characteristics of the circulating viruses were similar with the viruses from previously affected provinces during Wave Five.
A delayed peak of human infections was observed in the newly affected western Chinese provinces, and reassortment has been ongoing since the introduction of H7N9 viruses. Our study highlights the importance of continued surveillance of the circulation and evolution of H7N9 virus in western China.