背景:在COVID-19大流行期间实施的非药物干预措施导致全球流感感染显着减少。没有流感引起人们对免疫力下降的担忧,以及大流行后可能更严重的流感季节。
方法:为了评估对COVID-19大流行后流感的免疫力,我们评估了2016年10月至2023年6月在挪威的甲型流感流行情况,并通过血凝抑制(HAI)测定在2019年,2021年,2022年和2023年收集的总共3364份血清样本中,在不同年龄组中测量了针对甲型(H1N1)pdm09和甲型(H3N2)
结果:2016年10月至2023年6月在挪威的流感流行主要是流感,以A(H1N1)pdm09和A(H3N2)亚型为主的混合物。我们没有观察到COVID-19大流行后流感流行期间的感染人数高于COVID-19之前的季节。与2019年收集的血清相比,2021年和2022年收集的血清中针对A(H1N1)pdm09和A(H3N2)病毒的保护性HAI滴度的频率降低。减少可能,然而,在很大程度上可以解释为新病毒株的抗原漂移,由于保护性HAI滴度从一个季节到下一个季节对相同的菌株保持稳定。然而,我们观察到,在大流行期间,最年幼的儿童出现了免疫缺口,导致2021年和2022年针对A(H1N1)pdm09的HAI滴度显著下降.在2022/2023年A(H1N1)pdm09为主的流感季节之后,2023年收集的血清中的免疫差距部分缩小。在2022/2023年疫情期间,出现了属于5a.2a.1进化枝的A(H1N1)pdm09的漂移变体,与祖先5a.2进化枝相比,季前HAI滴度明显较低。
结论:在COVID-19后,观察到的针对A(H1N1)pdm09和A(H3N2)病毒的保护性抗体的减少最好地解释了新出现病毒的抗原漂移,并且在普通人群中抗体反应没有减弱。然而,大流行期间没有流感,导致了最小儿童的免疫力差距。尽管在2022/2023年流感季节之后,这种免疫力差距已部分缩小,严重感染风险升高的儿童应优先接种疫苗.
Non-pharmaceutical interventions implemented during the COVID-19 pandemic resulted in a marked reduction in influenza infections globally. The absence of influenza has raised concerns of waning immunity, and potentially more severe influenza seasons after the pandemic.
To evaluate immunity towards influenza post-COVID-19 pandemic we have assessed influenza A epidemics in Norway from October 2016 to June 2023 and measured antibodies against circulating strains of influenza A(H1N1)pdm09 and A(H3N2) in different age groups by hemagglutination inhibition (HAI) assays in a total of 3364 serum samples collected in 2019, 2021, 2022 and 2023.
Influenza epidemics in Norway from October 2016 until June 2023 were predominately influenza As, with a mixture of A(H1N1)pdm09 and A(H3N2) subtype predominance. We did not observe higher numbers of infections during the influenza epidemics following the COVID-19 pandemic than in pre-COVID-19 seasons. Frequencies of protective HAI titers against A(H1N1)pdm09 and A(H3N2) viruses were reduced in sera collected in 2021 and 2022, compared to sera collected in 2019. The reduction could, however, largely be explained by antigenic drift of new virus strains, as protective HAI titers remained stable against the same strain from one season to the next. However, we observed the development of an immunity gap in the youngest children during the pandemic which resulted in a prominent reduction in HAI titers against A(H1N1)pdm09 in 2021 and 2022. The immunity gap was partially closed in sera collected in 2023 following the A(H1N1)pdm09-dominated influenza seasons of 2022/2023. During the 2022/2023 epidemic, drift variants of A(H1N1)pdm09 belonging to the 5a.2a.1 clade emerged, and pre-season HAI titers were significantly lower against this clade compared to the ancestral 5a.2 clade.
The observed reduction in protective antibodies against A(H1N1)pdm09 and A(H3N2) viruses post COVID-19 is best explained by antigenic drift of emerging viruses, and not waning of antibody responses in the general population. However, the absence of influenza during the pandemic resulted in an immunity gap in the youngest children. While this immunity gap was partially closed following the 2022/2023 influenza season, children with elevated risk of severe infection should be prioritized for vaccination.