Communicable Disease Prevention and Control Services, British Columbia Centre for Disease Control, Vancouver, Canada.
PLoS One. 2013;8(1):e54015. doi: 10.1371/journal.pone.0054015. Epub 2013 Jan 11.
Cases of a novel swine-origin influenza A(H3N2) variant (H3N2v) have recently been identified in the US, primarily among children. We estimated potential epidemic attack rates (ARs) based on age-specific estimates of sero-susceptibility and social interactions. A contact network model previously established for the Greater Vancouver Area (GVA), Canada was used to estimate average epidemic (infection) ARs for the emerging H3N2v and comparator viruses (H1N1pdm09 and an extinguished H3N2 seasonal strain) based on typical influenza characteristics, basic reproduction number (R(0)), and effective contacts taking into account age-specific sero-protection rates (SPRs). SPRs were assessed in sera collected from the GVA in 2009 or earlier (pre-H1N1pdm09) and fall 2010 (post-H1N1pdm09, seasonal A/Brisbane/10/2007(H3N2), and H3N2v) by hemagglutination inhibition (HI) assay. SPR was assigned per convention based on proportion with HI antibody titre ≥40 (SPR40). Recognizing that the HI titre ≥40 was established as the 50%sero-protective threshold we also explored for ½SPR40, SPR80 and a blended gradient defined as: ¼SPR20, ½SPR40, ¾SPR80, SPR160. Base case analysis assumed R(0) = 1.40, but we also explored R(0) as high as 1.80. With R(0) = 1.40 and SPR40, simulated ARs were well aligned with field observations for H1N1pdm09 incidence (AR: 32%), sporadic detections without a third epidemic wave post-H1N1pdm09 (negligible AR<0.1%) as well as A/Brisbane/10/2007(H3N2) seasonal strain extinction and antigenic drift replacement (negligible AR<0.1%). Simulated AR for the novel swine-origin H3N2v was 6%, highest in children 6-11years (16%). However, with modification to SPR thresholds per above, H3N2v AR ≥20% became possible. At SPR40, H3N2v AR ≥10%, ≥15% or ≥30%, occur if R(0)≥1.48, ≥1.56 or ≥1.86, respectively. Based on conventional assumptions, the novel swine-origin H3N2v does not currently pose a substantial pandemic threat. If H3N2v epidemics do occur, overall community ARs are unlikely to exceed typical seasonal influenza experience. However risk assessment may change with time and depends crucially upon the validation of epidemiological features of influenza, notably the serologic correlate of protection and R(0).
最近在美国发现了新型猪源甲型流感病毒 A(H3N2)变体（H3N2v）病例，主要发生在儿童中。我们根据血清学敏感性和社会接触的年龄特异性估计了潜在的流行发病率（AR）。先前为加拿大大温哥华地区（GVA）建立的接触网络模型用于根据典型的流感特征、基本繁殖数（R(0)）和考虑年龄特异性血清保护率（SPR）的有效接触，估计新兴的 H3N2v 和比较病毒（H1N1pdm09 和已灭绝的 H3N2 季节性菌株）的平均流行（感染）AR。SPR 通过血凝抑制（HI）试验评估，该试验从 GVA 于 2009 年或更早（H1N1pdm09 之前）和 2010 年秋季（H1N1pdm09 之后，季节性 A/Brisbane/10/2007(H3N2)和 H3N2v）收集的血清进行。根据 HI 抗体滴度≥40（SPR40）的比例，按照惯例分配 SPR。鉴于 HI 滴度≥40 被确定为 50%的血清保护阈值，我们还探索了 ½SPR40、SPR80 和定义为：¼SPR20、½SPR40、¾SPR80、SPR160 的混合梯度。基础案例分析假设 R(0) = 1.40，但我们还探索了高达 1.80 的 R(0)。当 R(0) = 1.40 和 SPR40 时，模拟的 AR 与 H1N1pdm09 发病率的现场观察结果非常吻合（AR：32%），在 H1N1pdm09 之后没有第三次流行波的零星检测（可忽略不计的 AR<0.1%）以及 A/Brisbane/10/2007(H3N2)季节性菌株的灭绝和抗原漂移替代（可忽略不计的 AR<0.1%）。新型猪源 H3N2v 的模拟 AR 为 6%，在 6-11 岁儿童中最高（16%）。然而，通过上述 SPR 阈值的修改，H3N2v 的 AR≥20%是可能的。在 SPR40 下，如果 R(0)≥1.48、≥1.56 或≥1.86，则 H3N2v 的 AR≥10%、≥15%或≥30%。基于传统假设，新型猪源 H3N2v 目前不会构成重大大流行威胁。如果 H3N2v 确实发生流行，总体社区 AR 不太可能超过典型的季节性流感。然而，风险评估可能会随着时间的推移而发生变化，这取决于流感的流行病学特征的验证，尤其是血清学保护的相关因素和 R(0)。
