Background Annual influenza vaccination is the most effective way to prevent influenza. Influenza vaccines have traditionally included the hemagglutinins (HA) and neuraminidases (NA) from the two A viruses (H1N1 and H3N2) and either B Yamagata or B Victoria. Mismatches between circulating isolates of influenza B and the vaccines are very common. Taking 2017/2018 winter in northern hemisphere as an example, this study was designed to find out the reasons for mismatch between the trivalent influenza vaccine (TIV) and most of the epidemic isolates at that time, and to discuss if there are some optimized programs for seasonal influenza vaccines. Methods HA and NA sequences of the seasonal isolates circulating from December 1, 2017 to February 28, 2018, and in the previously other 7 winters in northern hemisphere from Global Initiative on Sharing All Influenza Data (GISAID) and the influenza database of National Center for Biotechnology Information (NCBI). Phylogenetic trees and genetic distances were constructed or calculated by using MAFFT and MEGA 6.0 software. Results Influenza B composition in the TIV recommendation mismatched most of circulating viruses in 2017/2018 winter; the vaccine strain was from the B/Victoria lineage, while most of epidemic isolates were from the B/Yamagata lineage. The epidemic lineage of influenza B reached its peak a little late in the previous winter might be responsible for this mismatch. During 2010-2018, the mean genetic distances between epidemic isolates of influenza A (H1N1 and H3N2) and the vaccines were no higher than 0.02375 ± 0.00341 in both HA and NA. However, concerning influenza B virus, when forecasting done well, the mean genetic distances between epidemic isolates and the vaccines were no higher than 0.02368 ± 0.00272; otherwise, the distances could reach 0.13695 ± 0.00238. Conclusion When applying quadrivalent influenza vaccines (QIVs) for vaccination, the recommendations of compositions for influenza B could be altered and assessed once in 3 or 4 years; when economic burden was considered intensively and TIVs were utilized, the recommended compositions for influenza B could be announced in April or May, rather than in February or March as now.

中文翻译：

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关于北半球季节性流感疫苗中乙型流感成分的争论。

背景 每年接种流感疫苗是预防流感最有效的方法。传统上，流感疫苗包含来自两种 A 病毒（H1N1 和 H3N2）以及 B Yamagata 或 B Victoria 的血凝素 (HA) 和神经氨酸酶 (NA)。流行的乙型流感病毒株与疫苗之间的不匹配非常常见。本研究以2017/2018年北半球冬季为例，旨在找出三价流感疫苗（TIV）与当时大部分流行分离株不匹配的原因，并探讨是否有一些优化方案用于季节性流感疫苗。方法 从全球流感数据共享倡议（GISAID）和国家流感中心流感数据库中获取2017年12月1日至2018年2月28日以及此前7个冬季在北半球流行的季节性分离株的HA和NA序列。生物技术信息（NCBI）。使用MAFFT和MEGA 6.0软件构建或计算系统发育树和遗传距离。结果 TIV推荐中的乙型流感成分与2017/2018冬季大多数流行病毒不匹配；疫苗株来自B/Victoria谱系，而大多数流行分离株来自B/Yamagata谱系。乙型流感的流行谱系在前一个冬天稍晚才达到顶峰，这可能是造成这种不匹配的原因。2010-2018年，HA和NA中甲型流感（H1N1和H3N2）流行分离株与疫苗之间的平均遗传距离均不高于0.02375±0.00341。然而，对于乙型流感病毒，当预测做得好时，流行分离株与疫苗之间的平均遗传距离不高于0.02368±0.00272；否则，距离可能达到 0.13695 ± 0.00238。结论 使用四价流感疫苗（QIV）进行疫苗接种时，乙型流感的成分建议可以每3年或4年更改和评估一次；当充分考虑经济负担并使用 TIV 时，乙型流感的推荐组合物可能会在 4 月或 5 月公布，而不是像现在这样在 2 月或 3 月公布。