Objective: To analyze the epidemiological characteristics, etiology and hemagglutinin (HA) gene characteristics of prevalent strains in Shandong Province from 2021 to 2022. Methods: The sentinel surveillance data of influenza-like illness (ILI) were collected in Shandong Province from 2021 to 2022. ILI specimens were detected with Real-Time PCR and virus isolation to explore the distribution of influenza viruses in different months. Three virus strains of each city were selected for gene sequencing, and the HA phylogenetic analysis was carried out. Results: In the surveillance-year from 2021 to 2022, 528 263 ILI cases were totally reported in 54 sentinel hospitals for influenza surveillance in Shandong Province. ILI visiting ratio (ILI%) was 4.07%, with the largest number in 0-4 age group (45.86%). The highly frequent season for ILI was in winter and spring, with a peak in the 52nd week, 2021 (6.62%). Totally, nucleic acid was detected in 26 754 specimens, with a positive rate of 27.10%, all of which were type B Victoria influenza. The positive rate reached a peak in the 49th week, 2021 (63.78%). A total of 295 outbreaks of ILI had been reported, in which 269 were positive for influenza virus. Most of outbreaks occurred in the primary school, with a peak in December. Gene evolution analysis showed that the HA gene in Shandong possessed high homology, 98.6% to 99.5%, with the recommended vaccine strains in 2020-2023, which was divided into two branches, V1A.3a.1 and V1A.3a.2. Conclusion: In the surveillance-year of 2021-2022, influenza is prevalent in December in Shandong Province, with a single circulating strain type. The positive rate of influenza virus and outbreak are higher than those in the previous surveillance-year. The circulating strain possesses high HA gene homology with those of the WHO vaccine recommended strains. However, the overall immune barrier of influenza virus is weak.
目的： 分析2021—2022年度山东省流感流行分布特征、流行毒株病原学及其血凝素（HA）基因特性。 方法： 收集2021—2022年度山东省流感样病例（ILI）哨点监测数据，进行描述性分析；采用荧光定量PCR核酸检测、病毒分离方法对采集的ILI标本开展检测，分析不同时间流感病毒的分布，按每市选取3株病毒进行基因测序，进行HA基因进化分析。 结果： 2021—2022年度，山东省54所流感监测哨点医院共报告ILI 528 263例，ILI就诊比例为4.07%，0~4岁ILI最多，为45.86%；呈冬春季流行高峰，最高峰为2021年第52周（6.62%）。共对26 754份标本开展了核酸检测，阳性率27.10%，均为B型Victoria系流感病毒，PCR阳性率高峰为2021年第49周（63.78%）；共报告ILI聚集性或暴发疫情295起，经实验室确诊269起为流感病毒阳性，以小学发生的疫情为主，2021年12月份报告疫情数最多。基因进化分析显示：HA基因与2020—2023年度推荐的疫苗株遗传距离均较近，介于98.6%~99.5%，且分成2个分支（V1A.3a.1，V1A.3a.2）。 结论： 2021—2022年度，山东省流感流行高峰在12月，毒株型别单一，流感病毒阳性率和暴发疫情报告数均较高，毒株与WHO疫苗推荐株HA基因同源性较好，但整体上流感病毒群体免疫屏障较弱。.