National Laboratory "Influenza and ARI", Department of Virology, National Center of Infectious and Parasitic Diseases, 44A Stoletov Blvd, 1233 Sofia, Bulgaria.
J Med Microbiol. 2024 Jul;73(7). doi: 10.1099/jmm.0.001864.
After two seasons of absence and low circulation, influenza activity increased significantly in the winter of 2022-2023. This study aims to characterize virological and epidemiological aspects of influenza infection in Bulgaria during the 2022-2023 season and perform a phylogenetic/molecular analysis of the hemagglutinin () and neuraminidase () sequences of representative influenza strains. Influenza A and B viruses generate new genetic groups/clades each season, replacing previously circulating variants. This results in increased antigenic distances from current vaccine strains. Strengthening existing influenza surveillance is essential to meet the challenges posed by the co-circulation of influenza and SARS-CoV-2. We tested 2713 clinical samples from patients with acute respiratory illnesses using a multiplex real-time RT-PCR kit (FluSC2) to detect influenza A/B and Severe acute respiratory syndrome coronavirus-2(SARS-CoV-2) simultaneously. Representative Bulgarian influenza strains were sequenced at the WHO Collaborating Centres in London, UK, and Atlanta, USA. Influenza virus was detected in 694 (25.6 %) patients. Of these, 364 (52.4 %), 213 (30.7 %) and 117 (16.9 %) were positive for influenza A(H1N1)pdm09, A(H3N2) and B/Victoria lineage virus, respectively. genes of the 47 influenza A(H1N1)pdm09 viruses fell into clades 5a.2. and 5a.2a.1 within the 6B.5A.1A.5a.2 group. Twenty-seven A(H3N2) viruses belonging to subclades 2b, 2a.1, 2a.1b and 2a.3a.1 within the 3C.2a1b.2a.2 group were analysed. All 23 sequenced B/Victoria lineage viruses were classified into the V1A.3a.2 group. We identified amino acid substitutions in and compared with the vaccine strains, including several substitutions in the antigenic sites. The study's findings showed genetic diversity among the influenza A viruses and, to a lesser extent, among B viruses, circulating in the first season after the lifting of anti-COVID-19 measures.
在经历了两个流感活动低水平的季节后，2022-2023 年冬季流感活动显著增加。本研究旨在描述保加利亚 2022-2023 年流感季节的病毒学和流行病学特征，并对代表株的血凝素（HA）和神经氨酸酶（NA）序列进行系统进化/分子分析。流感 A 和 B 病毒每季节都会产生新的遗传群/分支，取代之前流行的变体。这导致与当前疫苗株的抗原距离增加。加强现有的流感监测对于应对流感和严重急性呼吸综合征冠状病毒-2（SARS-CoV-2）共同流行带来的挑战至关重要。我们使用多重实时 RT-PCR 试剂盒（FluSC2）对 2713 份来自急性呼吸道疾病患者的临床样本进行了检测，以同时检测流感 A/B 和 SARS-CoV-2。在英国伦敦和美国亚特兰大的世界卫生组织合作中心对代表保加利亚的流感株进行了测序。在 694 名（25.6%）患者中检测到流感病毒。其中，364 名（52.4%）、213 名（30.7%）和 117 名（16.9%）患者的流感 A（H1N1）pdm09、A（H3N2）和 B/Victoria 系病毒呈阳性。47 株流感 A（H1N1）pdm09 病毒的 基因属于 6B.5A.1A.5a.2 组内的 5a.2.和 5a.2a.1 分支。属于 3C.2a1b.2a.2 组内的 2b、2a.1、2a.1b 和 2a.3a.1 亚分支的 27 株 A（H3N2）病毒被分析。所有 23 株测序的 B/Victoria 系病毒均被分类为 V1A.3a.2 组。与疫苗株相比，我们在 基因和 基因中发现了氨基酸取代，包括在 抗原位点的几个取代。本研究结果表明，在解除抗 COVID-19 措施后的第一个流感季节，流感 A 病毒之间以及 B 病毒之间存在遗传多样性。
