WHO《Science》答疑：H1N1会演变成1918流感吗？

　　

生物通报道，世界卫生组织的流感流行评估小组近日在《Science》杂志发表H1N1流感流行评估结果，分别将其与1957年和1918年的流感进行对比。

 

生物通编者按：近期中国内地的首例H1N1病例在四川成都被发现，H1N1的分布版图又扩大了，它又成功入侵了一个国家。面对流行范围越来越广的H1N1流感，全世界的科学家都束手无策，我们对H1N1的了解毕竟太少。有不少人担忧，新型流感病毒是否会变异，把流感疫情演变成1918年的西班牙大流感，甚至有人担忧新型H1N1会不会与H5N1重组。

 

会演变成1918流感吗？

5月11日，世界卫生组织（WHO）的流行评估小组（World Health Organization Rapid Pandemic Assessment Collaboration）在《Science》杂志发表H1N1研究的早期成果报告文章，Pandemic Potential of a Strain of Influenza A (H1N1) : Early Findings。文章一经发出收到Science和Nature等新闻的关注。

 

目前的研究分析表明，新型的H1N1流感病毒是继1957年流感（当时在杀死200万人）大流行后的具有危险性的病毒毒株，但是目前的数据显示新型的H1N1的死亡率远比1918流感低很多。

 

参与研究的伦敦皇家学院的流行病学家Neil Ferguson表示，毫无疑问，这一毒株有引起全球爆发的能力，不过令人欣慰的是，它的毒力还不至于引发人们的恐慌，它还没有禽流感那么可怕。

 

这次的国际合作研究数据主要来自墨西哥，这些数据来自墨西哥早期疫情，这些原始的数据有助科学家更全面的了解病毒，尤其对科学家对未来形势的预测具有重要的意义。

 

用数据说话

WHO分析了墨西哥6000-32000个病例，将流行数据与毒株的遗传信息整合进行分析，得出病毒的繁殖率数值，这一数值代表病毒繁殖传播的能力。WHO得出的数值为1.2-1.6，一般来说，季节性流感的病毒繁殖率在1.2左右，1918年的西班牙流感毒株的病毒繁殖率高达2。

 

一名没有参加此次研究的学者，华盛顿大学公共卫生学院的流行病学专家Ira Longini表示，这一数据表明，此次的流感严重性介于季节性流感和1918流感之间。但是，Longini同时还注意到一个细节，这次的分析数据来自非流感高发季节，因此不能全面的代表事实的真相，很难说在流感高发季节情况会不会也这样。

 

青年为何更易感？

这次的流感还有个特征，年轻人比老年人更易感。这一模式与季节性流感的不同。WHO的专家Ferguson称一个可能的解释是，季节性流感的毒株也是H1N1，相比小孩和年轻人来说，老年人在每个流感季节都有机会接触到H1N1，因此可能获得了某些抵抗力。当然，这也只是一个假设性的解释，目前还没有科学证据证实它。

（生物通  小茜）

 

参考文献

Fraser, C. et al. Science 10.1126/science.1176062 (2009).

Pandemic Potential of a Strain of Influenza A (H1N1) : Early Findings

Christophe Fraser 1, Christl A. Donnelly 1, Simon Cauchemez 1, William P. Hanage 1, Maria D. Van Kerkhove 1, T. Déirdre Hollingsworth 1, Jamie Griffin 1, Rebecca F. Baggaley 1, Helen E. Jenkins 1, Emily J. Lyons 1, Thibaut Jombart 1, Wes R. Hinsley 1, Nicholas C. Grassly 1, Francois Balloux 1, Azra C. Ghani 1, Neil M. Ferguson 1*, Andrew Rambaut 2, Oliver G. Pybus 3, Hugo Lopez-Gatell 4, Celia M Apluche-Aranda 5, Ietza Bojorquez Chapela 4, Ethel Palacios Zavala 4, Dulce Ma. Espejo Guevara 6, Francesco Checchi 7, Erika Garcia 7, Stephane Hugonnet 7, Cathy Roth 7, The WHO Rapid Pandemic Assessment Collaboration 

1 MRC Centre for Outbreak Analysis & Modelling, Department of Infectious Disease Epidemiology, Imperial College London, Faculty of Medicine, Norfolk Place, London W2 1PG, UK.

2 Institute of Evolutionary Biology, University of Edinburgh, Ashworth Laboratories Edinburgh EH9 3JT, UK.

3 Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.

4 Directorate General of Epidemiology, FCO. De P. Miranda 177 5th Floor, Mexico City, 01480, Mexico.

5 National Institute of Epidemiological Diagnosis and Reference, Prolongación Carpio No. 470 (3° piso), Col Santo Tomás, México City, C.P. 11340, Mexico.

6 Secretaría de Salud - Servicios de Salud de Veracruz Soconusco No. 36 Colonia Aguacatal C.P. 910 Xalapa, Veracruz, México State.

7 World Health Organization, 20 Av. Appia, 1211 Geneva, Switzerland.

* To whom correspondence should be addressed.

Neil M. Ferguson , E-mail: [e-mail]

These authors contributed equally to this work.

All authors are members of this collaboration.

 

A novel influenza A (H1N1) virus has spread rapidly across the globe. Judging its pandemic potential is difficult with limited data, but nevertheless essential to inform appropriate health responses. By analyzing the outbreak in Mexico, early data on international spread, and viral genetic diversity, we make an early assessment of transmissibility and severity. Our estimates suggest that 23,000 (range 6,000-32,000) individuals had been infected in Mexico by late April, giving an estimated case fatality ratio (CFR) of 0.4% (range 0.3% to 1.5%) based on confirmed and suspect deaths reported to that time. In a community outbreak in the small community of La Gloria, Veracruz no deaths were attributed to infection, giving an upper 95% bound on CFR of 0.6%. Thus while substantial uncertainty remains, clinical severity appears less than that seen in 1918 but comparable with that seen in 1957. Clinical attack rates in children in La Gloria were twice that in adults (<15 years-of-age: 61%, 15: 29%). Three different epidemiological analyses gave R0 estimates in the range 1.4-1.6, while a genetic analysis gave a central estimate of 1.2. This range of values is, consistent with 14 to 73 generations of human-to-human transmission having occurred in Mexico to late April. Transmissibility is therefore substantially higher than seasonal flu, and comparable with lower estimates of R0 obtained from previous influenza pan