The European Centre for Disease Prevention and Control is advising countries to prepare for a wave of pandemic H1N1 infections next winter and asks that the new seasonal vaccinations, which will contain the strain, be promoted for people likeliest to develop serious disease: children, pregnant women, and clinical risk groups.

In its “Forward Look Risk Assessment,” published March 8, the agency described the game-changing nature of the 2009 H1N1 pandemic, which crowded out the usual H3N1 and B strains in Europe, caused acute respiratory distress syndrome even in fit young adults, and infected the young more readily than the old. “The important thing for people to appreciate is when we go back to seasonal influenza, it won’t necessarily be the same seasonal influenza as we’ve had in the past,” Dr. Angus Nicoll, the ECDC’s influenza coordinator, said in an interview. “We may have to change who gets vaccinated.”

Whether target groups will get vaccinated will in large part depend on the countries they live in. In 2009, Poland refused to purchase any pandemic vaccine for its citizens, citing safety concerns, and other countries, such as Greece, saw low vaccination rates as a result of similar concerns. Both of these, along with a few other EU countries, continued to report significant disease activity, even as the pandemic dramatically ebbed in the rest of Europe.

Dr. Nicoll said he hoped that the European Medicines Agency’s reports on pandemic vaccine safety – the 12th of which was published last month – will have done enough to assuage the concerns of skeptical health officials before the next season begins.

The ECDC saw the likeliest scenario as a return of H1N1 not in the summer but rather during the winter, though other scenarios – and other viruses – were not discounted. “It is also most likely that pandemic influenza A(H1N1) will become the dominant virus in the coming winter season along with influenza B viruses, though the presence of influenza A(H3N2) viruses as well cannot presently be excluded,” the agency wrote.

The agency said it was especially concerned for the possibility that H1N1 could return in a more virulent or pathogenic form, citing the 1969-1970 flu season in which an H1N1 virus became more transmissible in its second winter. “Influenza viruses are notorious for their unpredictability,” ECDC wrote. “It should not be assumed that this will be the same as the previous seasonal influenza.”

Only last week, researchers at the Norwegian Institute of Public Health announced in the journal Eurosurveillance that they had found a mutation in 11 out of 61 viral samples taken from patients infected with 2009 pandemic H1N1 who developed severe or fatal disease. The mutation was not present in any of 205 mild cases also investigated (Euro. Surveill. 2010;15[9]:pII-19498).

One contingency not mentioned in ECDC’s March 8 report was the possibility of H5N1 strains causing disease in Europe, though parts of Asia continue to battle human cases of avian influenza, and Egypt reported its 105th this week. Dr. Nicoll said that though the ECDC “is not watching as vigorously as we were a few years ago,” it is not ignoring the threat posed by H5N1, either.

“The fact that the virus is still there and still very pathogenic for the few people it affects is concerning,” Dr. Nicoll said. “On the other hand the fact that it hasn’t started transmitting efficiently is encouraging. The size of the human-to-human clusters have declined – they certainly haven’t expanded.”

In a January issue of Eurosurveillance, which is published by ECDC but whose content is independent of the agency, researchers at Nigeria’s national veterinary institute concluded that “with the exceptional surge in number of cases (especially in children) arising in Egypt in 2009 and the recent reoccurrence of human cases of avian influenza A(H5N1) in China and Vietnam ... the pandemic potential of this virus is still very evident.” Also, the Nigerian team noted, the existence of pandemic H1N1 in Egypt alongside H5N1 “raises the possibility of co-infection and the emergence of reassortant viruses.”

The ECDC also drew attention last week to a report, published Feb. 22 in the journal PNAS, by researchers at the University of Wisconsin, Madison, who had generated 254 reassortments between currently co-circulating avian H5N1 and human H3N2 influenza strains. The team found that a mutation from an H3N2 strain isolated in Tokyo made the new viruses more pathogenic than did the parent viruses in 22 cases, and that three of the new viruses proved “extremely virulent” in mice. The findings, the researchers concluded, “highlight the importance of surveillance programs to monitor the emergence of human H5 reassortant viruses.

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欧洲疾病预防控制中心(ECDC)将建议各国为来年冬季新一轮的大流行性H1N1流感做好准备，同时还要求加快制备针对下列极高危感染患者的新型季节性流感疫苗(将含有相应病毒株)：儿童、孕妇及临床危险人群。

 

ECDC在3月8日发表的“风险评估预见”中描述了2009年度H1N1大流行的善变本质，该病毒将常见的H3N1和B毒株挤出欧洲，即使在健康的年轻人中亦引起急性呼吸窘迫综合征，与老年人相比，该感染更易累及年轻人。“人们需要认识到的重要一点是，季节性流感卷土重来时，其表现不一定与我们过去经历的季节性流感相同，”流感协调员Angus Nicoll博士在一次受访中说，“我们也许会被迫改变接种疫苗的对象。”

 

目标人群是否会获得免疫接种，这将在很大程度上取决于他们所居住的国家。2009年，处于对疫苗安全性的考虑，波兰拒绝为其公民购买任何类型的大流行性疫苗，而希腊等其他国家亦因为相同的顾虑致使疫苗接种率很低。这两国连同欧盟其他一些国家，即使在其余欧洲国家流感大流行情况大幅减少时，也不断有严重病情的报告。

 

Nicoll博士称，其本人希望欧洲药品管理局有关大流行性疫苗安全性的报告(上月发表了第12篇报告)能在下一季流感开始前充分消除持怀疑态度卫生官员的顾虑。

 

ECDC预计，H1N1最可能复发于冬季而非夏季，尽管其他感染情况——及其他病毒——并无减少。“大流行性甲型流感(H1N1)病毒与乙型流感病毒也极有可能成为来年冬季的主要病毒，尽管目前也不排除出现甲型H3N2病毒的情况，”ECDC写道。

 

ECDC指出，其尤为担心的是，复发的H1N1病毒致病力可能更强，以1969~1970年的流感季节为例，该季节N1N1流感病毒的传染性在其下一个冬季中增强。“流感病毒因其不可预知性而令人棘手，”ECDC写道，“我们不应认为本季的发病情况与前一季相同。”

 

就在上周，挪威公共卫生学院的研究者在《欧洲监控》(Eurosurveillance)杂志上宣布，他们已发现在61个病毒样本中有11个发生变异，这些病毒样本取自2009年感染大流行性H1N1、发生重度或致死性流感的患者。在同期检查的205例取自轻度感染患者的样本中未发现这种变异(Euro. Surveill. 2010;15[9]:pII-19498)。

 

ECDC  3月8日的报告中未提及的一起意外事故为，尽管亚洲部分国家在继续同人感染禽流感作斗争，但H5N1病毒株仍可能在欧洲致病，本周埃及报告了其第105例禽流感病例。Nicoll博士指出，尽管ECDC“不再像几年前那样积极地关注禽流感，”但也不会忽略H5N1所致的威胁。

 

 “病毒仍存在，且对其感染的少数人仍有极强的致病性，这一事实令人担忧，”Nicoll博士说，“另一方面，该病毒尚未开始有效地传播，这一情况又令人信心倍增。这种人传人的感染规模尚未缩减——但可以肯定的是，感染规模未扩大。”

 

尼日利亚国家兽医研究所的研究者们在《欧洲监控》(Eurosurveillance)1月刊(由ECDC发表但其内容与该机构无关)中断言，“2009年埃及流感病例(特别是儿童)意外蜂拥而至，中国和越南等国近期人感染禽流感病例再次出现……这种病毒的大流行潜力仍很明显。”尼日利亚研究团队还强调指出，埃及大流行性H1N1病毒与H5N1的存在可能会导致合并感染的发生和病毒重配株的出现。”

 

上周ECDC还关注了2月22日发表在《美国国家科学院院刊》(PNAS)上的一项报告，其作者为威斯康辛州立大学麦迪逊分校的研究者，他们在当前同时流行的禽流感H5N1病毒株与人H3N2流感病毒株之间构建了254种病毒重配株。该研究小组发现，与22个病例中的亲代病毒相比，由在东京分离出的H3N2病毒株变异后形成的新病毒致病力更强，其中3种病毒株对小鼠的致病力“极强”。研究者们推断，这些结果“突显了用于监测人H5重组病毒出现的监控程序的重要性。”

 

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