Flu-BPD, AstraZeneca, Liverpool, UK.
Flu-BPD, AstraZeneca, Liverpool, UK.
Vaccine. 2020 May 27;38(26):4209-4218. doi: 10.1016/j.vaccine.2020.04.004. Epub 2020 May 4.
In the 2013-2014 and 2015-2016 influenza seasons, live attenuated influenza vaccine (LAIV) generated reduced vaccine effectiveness (VE) against circulating H1N1 strains. This reduced VE coincided with the introduction of pandemic 2009 H1N1 (A/H1N1pdm09) vaccine virus reassortants, in place of pre-2009 seasonal H1N1 strains. Here, we explored one specific hypothesis for reduced VE; decreased replicative fitness of A/H1N1pdm09 strains in humans. Two A/H1N1pdm09 strains with reduced VE, A/California/07/2009 (A/CA09) and A/Bolivia/559/2013 (A/BOL13), were compared to pre-2009 seasonal H1N1 strains, A/New Caledonia/20/1999 (A/NC99) and A/South Dakota/6/2007 (A/SD07). Initial results showed that A/H1N1pdm09 strains had reduced multi-cycle infectivity in Madin-Darby Canine Kidney (MDCK) cells, compared to their pre-2009 counterparts. The A/BOL13 viral titre was found to be 2.65 log/mL lower when measured by multi-cycle 50% tissue culture infectious dose (TCID) assay compared to single-cycle fluorescent focus assay (FFA). By contrast, clinically effective A/NC99 titres differed by only 0.54 log/mL. In human alveolar (A549) cells, A/H1N1pdm09 strains replicated less than pre-2009 strains, with A/CA09 and A/BOL13 generating lower peak viral titres over 5 days. This phenotype was corroborated in physiologically relevant, primary human nasal epithelial cells (hNECs). Here, peak titres for pre-2009 strains A/NC99 and A/SD07 were 8.43 log TCID/mL and 8.52 log TCID/mL, respectively, versus 6.89 log TCID/mL and 6.06 log TCID/mL for A/H1N1pdm09 strains A/CA09 and A/BOL13. This confirmed a reduced ability of A/H1N1pdm09 strains to sustain replication in human respiratory cells. Using this information, H1N1 candidate A/Slovenia/2903/2015 (A/SLOV15) was characterised for replacement of A/BOL13 in the 2017/18 LAIV. A/SLOV15 produced comparable single and multi-cycle infectivity titres (Δ 0.16 log/mL) and reached a peak titre 1.23 log TCID/mL higher than that of A/BOL13 in hNEC cultures. Taken together, these data suggest a reduction in sustained multi-cycle replication in human cells as a plausible root cause for reduced A/H1N1pdm09 VE.
在 2013-2014 年和 2015-2016 年流感季节，减毒活流感疫苗（LAIV）对循环 H1N1 株的疫苗有效性（VE）降低。这种降低的 VE 恰逢大流行 2009 年 H1N1（A/H1N1pdm09）疫苗病毒重组的引入，取代了 2009 年前的季节性 H1N1 株。在这里，我们探讨了一种降低 VE 的具体假设；A/H1N1pdm09 株在人类中的复制适应性降低。两种 VE 降低的 A/H1N1pdm09 株，A/加利福尼亚/07/2009（A/CA09）和 A/玻利维亚/559/2013（A/BOL13），与 2009 年前的季节性 H1N1 株，A/新喀里多尼亚/20/1999（A/NC99）和 A/南达科他州/6/2007（A/SD07）进行了比较。最初的结果表明，与 2009 年前的株相比，A/H1N1pdm09 株在 Madin-Darby 犬肾（MDCK）细胞中的多周期感染性降低。与单次循环荧光焦点测定（FFA）相比，通过多周期 50%组织培养感染剂量（TCID）测定，发现 A/BOL13 病毒滴度低 2.65 log/mL。相比之下，临床上有效的 A/NC99 滴度仅相差 0.54 log/mL。在人肺泡（A549）细胞中，A/H1N1pdm09 株的复制能力低于 2009 年前的株，A/CA09 和 A/BOL13 在 5 天内产生的峰值病毒滴度较低。这一表型在生理相关的原代人鼻上皮细胞（hNEC）中得到了证实。在这里，2009 年前的株 A/NC99 和 A/SD07 的峰值滴度分别为 8.43 log TCID/mL 和 8.52 log TCID/mL，而 A/H1N1pdm09 株 A/CA09 和 A/BOL13 的峰值滴度分别为 6.89 log TCID/mL 和 6.06 log TCID/mL。这证实了 A/H1N1pdm09 株在人呼吸道细胞中维持复制的能力降低。利用这些信息，对候选 A/Slovenia/2903/2015（A/SLOV15）株进行了特征描述，以取代 2017-18 年 LAIV 中的 A/BOL13。A/SLOV15 产生了可比的单次和多周期感染性滴度（Δ 0.16 log/mL），在 hNEC 培养物中达到的峰值滴度比 A/BOL13 高 1.23 log TCID/mL。综上所述，这些数据表明，A/H1N1pdm09 株在人细胞中持续多周期复制能力的降低是 VE 降低的一个合理原因。
