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作者：Laurie Barclay, MD  
出處：WebMD醫學新聞

　　October 7, 2009 — 根據線上發表於10月6日英國醫學期刊(British Medical Journal)的一篇墨西哥市群體配對、案例控制研究結果，季節性流感疫苗有助於預防新型A型流感(H1N1)。不過，研究者與編輯評論作者都認為，仍需要針對H1N1流感病毒的疫苗進行研究。
　　
　　墨西哥奎瓦那國立de Salud Publica研究中心的Lourdes Garcia-Garcia等人寫道，包括一個從墨西哥人分離的多個新型A型/H1N1病毒株的病毒基因序列，已經公諸於世。因為這是個新的重組病毒，也就是說混合了豬、禽與人類的流感基因序列，現有的證據雖不完整，但研究者認為，季節性流感疫苗對於A型/H1N1病毒略有保護力或者沒有保護力。墨西哥的指引建議，3價無活性流感疫苗(病毒株包括 A/Brisbane/59/2007 (H1N1)-類、A/Brisbane/10/2007 (H3N2)- 類與 B/Florida/4/2006-類抗原)用於6至35個月孩童、60歲以上成人、35個月以上有造成流感相關併發症高風險之狀況者。
　　
　　研究目標是評估2008至2009年季節性3價無活性疫苗與墨西哥A型/H1N1流感案例的關聯。在墨西哥市的一個專科醫院中，從2009年3至5月，比較60位經實驗室確認為A型/H1N1流感的病患以及180名年紀和社經狀態相符的對照組。對照組有類流感或肺炎之外的疾病，住在墨西哥市或墨西哥州。初級研究終點為3價無活性疫苗對抗A型/H1N1流感的勝算比(OR)以及效果。
　　
　　相較於對照組，實驗室確認為A型/H1N1流感的病患有較高的住院率、侵犯性機械輔助呼吸與死亡。不過，對照組病患比實驗室確認為A型/H1N1流感的病患更可能有流感相關併發症高風險的慢性狀況。根據多變項模式，H1N1流感與接受3價無活性疫苗(OR，0.27；95%信心區間[CI]，0.11 – 0.66)以及原本的狀況(OR，0.15；95% CI，0.08 – 0.30)無關。3價無活性疫苗對於H1N1流感的效力為73% (95% CI，34% –89%)，施打疫苗之8位經實驗室確認為A型/H1N1流感的病患無人死亡。
　　
　　研究作者寫道，初步證據認為，在墨西哥市的流感流行期間於某專科醫院的診斷發現，2008至2009年之3價無活性疫苗對於2009年A型/H1N1流感有一些保護力，特別是重症。這些結果需慎重評估，也不代表季節性流感可以取代2009年A型/H1N1流感疫苗。我們的資料支持季節性流感有部份保護力的假設，這可能是因為加強了既有曝露(不論是感染或疫苗)時產生的A型/H1N1流感病毒抗體，基因上和抗原上比季節性H1N1病毒株更接近現有的新流感病毒。
　　
　　研究限制包括，這是回溯研究、樣本少、自我報告疫苗狀態，訪問者知道實驗室確認為A型/H1N1流感的病患和對照組病患的分類。
　　
　　研究作者結論表示，在我們的控制組中，因為慢性狀況和施打疫苗的高盛行率，估計的疫苗效果會被誇大。需要其他族群的類似研究，以確認或推翻我們的結果。
　　
　　荷蘭阿姆斯特丹大學附設醫學中心的Menno D. de Jong和紐約市康乃爾大學Weill醫學院的Rogier W. Sanders在編輯評論中也提到，還是需要針對A型流感(H1N1)的疫苗。即使在安排疫苗足量生產的國家，疫苗也可能無法及時供應。
　　
　　De Jong醫師和Sanders醫師寫道，可以辨識多種流感病毒株的抗體很少，這可以用來解釋疫苗和天然感染之間經常缺乏交叉保護力。不過，確認抗體後可能可以開啟研發「萬用型流感疫苗」的可能性。傳統流感疫苗在效果和安全上有良好的紀錄，所以要好幾年才能取代它們，但是依舊需要新技術與進行各階段試驗的疫苗。
　　
　　墨西哥衛生部支持本研究。2名研究作者受雇於Laboratorios de Biol?gicos y Reactivos de M?xico。De Jong醫師與 Sanders醫師皆宣告沒有相關財務關係。
　　
　　BMJ. 線上發表於2009年10月6日。

Seasonal Flu Vaccine May Help Protect Against H1N1

By Laurie Barclay, MD
Medscape Medical News

October 7, 2009 — Seasonal influenza vaccine may help protect against novel pandemic influenza A (H1N1), according to the results of a frequency-matched, case-control study in Mexico City reported online October 6 in the British Medical Journal. However, the investigators and authors of an accompanying editorial urge that a specific vaccine against H1N1 flu is still needed.

"The viral genomic sequence for several of the novel A/H1N1 strains, including a Mexican isolate, has been made publicly available," write Lourdes Garcia-Garcia, from Instituto Nacional de Salud Publica in Cuernavaca, Mor, Mexico, and colleagues. "Given the new reassortant nature of this virus — that is, unusual mixing of swine, avian, and human influenza genetic sequences — the available evidence, although incomplete, suggests that seasonal vaccines will confer little or no protection against influenza A/H1N1. Mexican guidelines recommend vaccination with trivalent inactivated influenza vaccine (virus strains A/Brisbane/59/2007 (H1N1)-like, A/Brisbane/10/2007 (H3N2)-like, and B/Florida/4/2006-like antigen) for children aged 6-35 months, all adults aged more than 60, and individuals older than 35 months with conditions conferring a higher risk of influenza related complications."

The goal of this study was to examine the association of 2008–2009 seasonal trivalent inactivated vaccine with cases of influenza A/H1N1 during the epidemic in Mexico. From March to May 2009 at a specialty hospital in Mexico City, 60 patients with laboratory-confirmed influenza A/H1N1 were compared with 180 control patients matched for age and socioeconomic status. Control subjects had diseases other than influenza-like illness or pneumonia and were living in Mexico City or the state of Mexico. The primary study endpoints were odds ratio (OR) and effectiveness of trivalent inactivated vaccine against influenza A/H1N1.

Compared with control patients, patients with laboratory-confirmed influenza A (H1N1) had higher rates of hospitalization, invasive mechanical ventilation, and death. However, control patients were more likely than patients with laboratory-confirmed influenza A (H1N1) to have chronic conditions associated with a higher risk for influenza-related complications. H1N1 influenza was independently associated with receipt of trivalent inactivated vaccine (OR, 0.27; 95% confidence interval [CI], 0.11 – 0.66) and with underlying conditions (OR, 0.15; 95% CI, 0.08 – 0.30), based on the multivariate model. Trivalent inactivated vaccine effectiveness against H1N1 influenza was 73% (95% CI, 34% – 89%), and none of the 8 vaccinated patients with laboratory-confirmed influenza A (H1N1) died.

"Preliminary evidence suggests some protection from the 2008-9 trivalent inactivated vaccine against pandemic influenza A/H1N1 2009, particularly severe forms of the disease, diagnosed in a specialty hospital during the influenza epidemic in Mexico City," the study authors write. "These results are to be considered cautiously and in no way indicate that seasonal vaccine should replace vaccination against pandemic influenza A/H1N1 2009. Our data support the hypothesis that partial protection provided by the seasonal vaccine may be explained by the boosting of existing antibodies that were elicited by previous exposure, through either infection or vaccination, to an influenza A/H1N1 virus genetically and antigenically more closely related to the novel influenza virus than contemporary seasonal H1N1 strains."

Limitations of this study include its retrospective design, small sample size, self-reported vaccine status, and lack of blinding of interviewers to the status of patients with laboratory-confirmed influenza A (H1N1) and control patients.

"The estimates for vaccine effectiveness could be inflated owing to a high prevalence of chronic conditions and vaccination in our control population," the study authors conclude. "Similar studies in other settings are needed to confirm or refute our results."

In an accompanying editorial, Menno D. de Jong, from the Academic Medical Centre of the University of Amsterdam, the Netherlands, and Rogier W. Sanders, from Weill Medical College of Cornell University, New York City, also warn that a specific vaccine against influenza A (H1N1) is still needed. Even in countries that have arranged for vaccine production in sufficient quantities, vaccines may not be available in time.

"Antibodies that recognise multiple influenza strains are rare, which explains the frequent lack of cross protection between vaccines and natural infection," Dr. De Jong and Dr. Sanders write. "However, antibodies have been identified that may open possibilities of developing a 'universal flu vaccine.' Traditional flu vaccines have a good track record in terms of efficacy and safety, so it will take years to replace them, but the new techniques and vaccines at various stages of testing are both necessary and promising."

The Mexican Ministry of Health supported this study. Two of the study authors are employed by Laboratorios de Biologicos y Reactivos de Mexico. Dr. De Jong and Dr. Sanders have disclosed no relevant financial relationships.

BMJ. Published online October 6, 2009.