National Laboratory "Influenza and ARI", Department of Virology, National Center of Infectious and Parasitic Diseases, Sofia, Bulgaria.
J Med Virol. 2023 Feb;95(2):e28489. doi: 10.1002/jmv.28489.
Social distancing, mask-wearing, and travel restrictions during the COVID-19 pandemic have significantly impacted the spread of influenza viruses. The objectives of this study were to analyze the pattern of influenza virus circulation with respect to that of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in Bulgaria during the 2021-2022 season and to perform a phylogenetic/molecular analysis of the hemagglutinin (HA) and neuraminidase (NA) sequences of representative influenza strains. Influenza infection was confirmed using real-time reverse transcription polymerase chain reaction in 93 (4.2%) of the 2193 patients with acute respiratory illness tested wherein all detected viruses were subtyped as A(H3N2). SARS-CoV-2 was identified in 377 (24.3%) of the 1552 patients tested. Significant differences in the incidence of influenza viruses and SARS-CoV-2 were found between individual age groups, outpatients/inpatients, and in the seasonal distribution of cases. Two cases of coinfections were identified. In hospitalized patients, the C values of influenza viruses at admission were lower in adults aged ≥65 years (indicating higher viral load) than in children aged 0-14 years (p < 0.05). In SARS-CoV-2-positive inpatients, this association was not statistically significant. HA genes of all A(H3N2) viruses analyzed belonged to subclade 3C.2a1b.2a. The sequenced viruses carried 11 substitutions in HA and 5 in NA, in comparison to the vaccine virus A/Cambodia/e0826360/2020, including several substitutions in the HA antigenic sites B and C. This study revealed extensive changes in the typical epidemiology of influenza infection, including a dramatic reduction in the number of cases, diminished genetic diversity of circulating viruses, changes in age, and seasonal distribution of cases.
在 COVID-19 大流行期间，社交距离、戴口罩和旅行限制极大地影响了流感病毒的传播。本研究的目的是分析 2021-2022 年保加利亚流感病毒与严重急性呼吸综合征冠状病毒 2（SARS-CoV-2）的流行模式，并对代表流感株的血凝素（HA）和神经氨酸酶（NA）序列进行系统发育/分子分析。在 2193 例急性呼吸道疾病患者中，使用实时逆转录聚合酶链反应（PCR）检测到 93 例（4.2%）流感感染病例，所有检测到的病毒均被亚型化为 A（H3N2）。在 1552 例检测的患者中，鉴定出 377 例（24.3%）SARS-CoV-2。在不同年龄组、门诊/住院患者和病例的季节性分布中，流感病毒和 SARS-CoV-2 的发病率存在显著差异。鉴定出两例合并感染病例。在住院患者中，入院时流感病毒的 C 值在年龄≥65 岁的成年人（表明病毒载量更高）中低于 0-14 岁的儿童（p<0.05）。在 SARS-CoV-2 阳性住院患者中，这种相关性没有统计学意义。分析的所有 A（H3N2）病毒的 HA 基因属于亚谱系 3C.2a1b.2a。与疫苗病毒 A/Cambodia/e0826360/2020 相比，测序病毒在 HA 上携带 11 个替换，在 NA 上携带 5 个替换，包括在 HA 抗原位点 B 和 C 上的几个替换。本研究揭示了流感感染典型流行病学的广泛变化，包括病例数量的急剧减少、循环病毒遗传多样性的降低、病例年龄和季节性分布的变化。
