WHO的新標準可能將更多流感病毒列為大流行株

　　【24drs.com】November 3, 2009 — 根據一項發表於11月2日英國醫學期刊：臨床證據（British medical journal：clinical evidence）的主編評論，由世界衛生組織（WHO）重新定義的大流行條件，可能下降虛報的風險。採用新的WHO標準可能使得更多流感病毒株符合大流行標準。
　　
　　新澤西醫學院與牙醫學院Hackensack大學醫學中心的Peter A. Gross醫師寫到，當流感病毒發生變化時，公共衛生學界使用可靠的、平衡的標準來評量流感大爆發的或然率是很重要的。WHO對於流感爆發最近改變的定義造成了很大的困惑。
　　
　　2005年WHO的標準宣稱大爆發必須有抗原轉移，且必須有出現新的流感亞型，例如從A（H2N2）轉變成A（H3N2），然而，新的定義將會使任何流感病毒出現轉移、或是從原來亞型突變，如果它出現快速的人傳人，則符合大爆發的菌株。
　　
　　要預測會有多少人因為感染特定病毒株而發病或是死亡，經常是很困難的，指向目前的A型流感（H1N1）大流行，目前並未如預期的那樣大規模流行。
　　
　　然而，全新的A型流感（H1N1）病毒株，只是飄移而非轉移病毒株，以最新的檢驗技術，在抗原上與基因上都與季節性A型流感（H1N1）病毒株差異很大。
　　
　　Gross博士寫到，在未來，WHO應該澄清目前對流感大流行的定義，納入任何亞型轉移，且飄移病毒株當同樣亞型的季節性病毒株出現顯著抗原與基因上的差異。
　　
　　主編描述額外的證據顯示群眾對於全新A型流感（H1N1）在免疫上並非完全陌生，且較年輕的族群可能因為過去曾暴露於A型流感（H1N1）病毒，不論是自然情況下或是透過接種疫苗，而有所準備。
　　
　　Gross博士的結論是，季節性流感將會繼續發生，且高危險群以及那些想要免於流感感染的病患，應該每年接種包含三種流感病毒亞群，A型流感（H3N2）病毒株、A型流感（H1N1）病毒株、以及B型流感的流感疫苗。為了預防受到新型A型流感（H1N1）感染，那些處於高風險的人們（包括孕婦、有慢性心臟或呼吸疾病、糖尿病或免疫功能不全患者）都應該遵守國家發佈的指引，接種新的2009年全新A型流感（H1N1）病毒株一價疫苗。

New WHO Criteria May Qualify More Flu Viruses as Pandemic Strains

By Laurie Barclay, MD
Medscape Medical News

November 3, 2009 — Refining the pandemic criteria recently issued by the World Health Organization (WHO) might reduce the risk for a false alarm, according to an editorial reported online November 2 in the British Medical Journal: Clinical Evidence. Application of the new WHO criteria may result in more influenza viruses qualifying as pandemic strains.

"When changes occur in the influenza virus, it is important that the public health community use reliable, balanced criteria to evaluate the probability of an influenza pandemic," writes Peter A. Gross, MD, from Hackensack University Medical Center, University of Medicine and Dentistry of New Jersey–New Jersey Medical School. "Recent changes in the WHO's definition of a pandemic flu have caused significant confusion."

The 2005 WHO criteria for declaring a pandemic require an antigenic shift, or appearance of a new influenza subtype, such as a change from A (H2N2) to A (H3N2), whereas the new definition would result in almost any influenza virus demonstrating drift, or mutation from the original subtype, to qualify as a pandemic strain if it showed rapid transmission from human to human.

It is often difficult to predict how much morbidity and mortality will ensue from infection with a particular virus strain — case in point being the current influenza A (H1N1) pandemic, which thus far has not been as severe as one would expect from a true pandemic.

Nonetheless, the novel A (H1N1) influenza strain, which is only a drifted and not a shifted strain, is significantly divergent from seasonal A (H1N1) strains antigenically and genetically, as determined by advanced testing technology.

"In the future, it would be more appropriate for the WHO to clarify its current definition of an influenza pandemic virus to include any shifts in subtype, and only drifted strains which exhibit significant antigenic and genetic divergence from the seasonal strain of the same subtype," Dr. Gross writes.

The editorial describes additional evidence suggesting that the population is not completely immunologically naive to the novel A (H1N1) and that the younger population may have already been primed by previous exposure to an A (H1N1) virus, either naturally or through vaccination.

"Seasonal influenza will continue to occur, and annual immunisation with the trivalent vaccine containing three influenza strains — an A (H3N2) strain, an A (H1N1) strain, and a B strain — should continue for high-risk groups and people who want to avoid influenza infection," Dr. Gross concludes. "For prevention of infection with the novel A (H1N1), those at high risk (including pregnant women, those with chronic cardiac or respiratory diseases, diabetes, or immunosuppression) should receive the new monovalent vaccine for the 2009 novel A (H1N1) strain as recommended by national guidelines."

BMJ. Published online November 2, 2009.