The development of influenza candidate vaccine viruses (CVVs) for pre-pandemic vaccine production represents a critical step in pandemic preparedness. The multiple subtypes and clades of avian or swine origin influenza viruses circulating world-wide at any one time necessitates the continuous generation of CVVs to provide an advanced starting point should a novel zoonotic virus cross the species barrier and cause a pandemic. Furthermore, the evolution and diversity of novel influenza viruses that cause zoonotic infections requires ongoing monitoring and surveillance, and, when a lack of antigenic match between circulating viruses and available CVVs is identified, the production of new CVVs. Pandemic guidelines developed by the WHO Global Influenza Program govern the design and preparation of reverse genetics-derived CVVs, which must undergo numerous safety and quality tests prior to human use. Confirmation of reassortant CVV attenuation of virulence in ferrets relative to wild-type virus represents one of these critical steps, yet there is a paucity of information available regarding the relative degree of attenuation achieved by WHO-recommended CVVs developed against novel viruses with pandemic potential. To better understand the degree of CVV attenuation in the ferret model, we examined the relative virulence of six A/Puerto Rico/8/1934-based CVVs encompassing five different influenza A subtypes (H2N3, H5N1, H5N2, H5N8, and H7N9) compared with the respective wild-type virus in ferrets. Despite varied virulence of wild-type viruses in the ferret, all CVVs examined showed reductions in morbidity and viral shedding in upper respiratory tract tissues. Furthermore, unlike the wild-type counterparts, none of the CVVs spread to extrapulmonary tissues during the acute phase of infection. While the magnitude of virus attenuation varied between virus subtypes, collectively we show the reliable and reproducible attenuation of CVVs that have the A/Puerto Rico/9/1934 backbone in a mammalian model.

用于大流行前疫苗生产的流感候选疫苗病毒（CVV）的开发是大流行防范的关键一步。禽或猪源流感病毒的多种亚型和进化枝随时在世界范围内传播，因此需要连续生成 CVV，以便在新型人畜共患病毒跨越物种屏障并引起大流行时提供先进的起点。此外，引起人畜共患感染的新型流感病毒的进化和多样性需要持续监测和监视，并且当发现流行病毒与可用的 CVV 之间缺乏抗原匹配时，需要生产新的 CVV。世界卫生组织全球流感规划制定的大流行指南指导了反向遗传学衍生的 CVV 的设计和制备，这些 CVV 在人类使用之前必须经过大量的安全和质量测试。确认雪貂相对于野生型病毒的重配 CVV 毒力减弱是这些关键步骤之一，但关于 WHO 推荐的针对具有大流行潜力的新型病毒开发的 CVV 所实现的相对减毒程度的信息很少。为了更好地了解雪貂模型中 CVV 的衰减程度，我们比较了包含五种不同甲型流感亚型（H2N3、H5N1、H5N2、H5N8 和 H7N9）的六种基于 A/Puerto Rico/8/1934 的 CVV 的相对毒力。与雪貂体内各自的野生型病毒。尽管雪貂中野生型病毒的毒力各不相同，但所有检查的 CVV 均显示上呼吸道组织的发病率和病毒脱落有所减少。此外，与野生型对应物不同，CVV 在感染急性期不会扩散到肺外组织。虽然病毒减毒的程度因病毒亚型而异，但我们总的来说在哺乳动物模型中展示了具有 A/Puerto Rico/9/1934 主干的 CVV 的可靠且可重复的减毒作用。