0.05).Conclusion The group of 13 months age of infants were rarely infected influenza virus in the first time exposure at the age of ≤4 months due to maternal antibodies protection.Whenas,the group of 8 months age who were exposed at the age of ≥5 months,were more easier infected the influenza virus than the group of 13 months age in the first time exposure at the age of ≤4 months.

Objective:To disclose the epidemiological characteristics of severe fever with thrombocytopenia syndrome in Ningbo city from 2013 to 2021.Methods:Epidemic data and laboratory-confirmed results of SFTS patients in Ningbo city were analyzed in the past 10 years. Phylogenetic trees were constructed by using genomic sequences of severe fever with thrombocytopenia syndrome virus (SFTSV) strains isolated from the patients.Results:During 2013-2021, a total of 65 confirmed SFTS cases were reported with the mortality of 12.31%, including 8 dead cases. The average age was 53.65 years with higher incidence in 60-70 years old cases. Cases were reported in 6 districts (counties) from Ningbo city, of which Ninghai county (33 cases, 50.77%) and Xiangshan county (20 cases, 30.77%) reported the highest number of cases. The cases mainly occurred from April to August, accounting for 81.54% (53/65); 76.92% (50/65) of the patients were farmers; 92.31% (60/65) of patients lived in mountainous or hilly terrain. Of the 65 SFTS cases, 8 patients had a clear history of tick bites, and 20 patients had contact with domestic animals (pets) or rats in their residence. The evolution analysis on gene sequencing results showed that SFTSV epidemic strains in Ningbo city included genotype J2 and C4.Conclusion:Most of the SFTS patients were elderly people. The top two high-risk areas were Ninghai county and Xiangshan county. July was the peak month of the disease. Genotype J2 and C4 were epidemic strains in Ningbo city.