Pandemic influenza A(H1N1) infections in the United States rose to the highest levels so far this season, according to data collected through Oct. 3— the most recent data available to the Centers for Disease Control and Prevention.

The proportion of outpatient visits for influenza-like illness reached 5.1% during September 27 through October 3, surpassing H1N1 activity last spring and reaching the highest level of U.S. flu activity since the seasonal flu outbreak in early 2008. During the week ending October 3, 37 states had widespread flu activity, up from 27 states the prior week.

The outbreaks also show no pattern of lower numbers of new infections in cities that were hard hit by H1N1 flu last spring, Dr. Anne Schuchat, director of the CDC’s National Center for Immunization and Respiratory Diseases, said in a press briefing October 9.

The CDC looked specifically at about 50 U.S. cities and found several with rising flu case numbers despite H1N1 outbreaks in spring 2009. This finding deflates the hypothesis that a significant level of H1N1 herd immunity may blunt the rate of new infections. “It’s way too soon for us to be certain about a second or third wave” of H1N1 flu, Dr. Schuchat said. Despite last spring’s outbreaks the vast majority of people remain susceptible to H1N1, she added.

Recent H1N1 activity also added to the death toll in children younger than 18. The week ending October 3 added 19 new pediatric deaths from H1N1 flu, bringing the total since the virus emerged last April to 76 pediatric deaths. About a quarter of these children had no underlying disease, although many had coninfections. This compared with a total of 46-88 pediatric deaths during the prior three flu seasons, suggesting the current season may surpass those levels, Dr. Schuchat said.

The briefing also included updates on trials run by the U.S. National Institute of Allergy and Infectious Diseases to test the H1N1 vaccine. The most important new finding was early results showing that simultaneous administration of the H1N1 and seasonal flu vaccines has no effect on their protection, said Dr. Anthony Fauci, NIAID’s director. The early results came from 50 people in a trial involving 400 healthy adults and 400 healthy elderly people that began in August.

He also updated results from a study that assessed the efficacy of a single, unadjuvanted, 15 mcg dose of injected H1N1 vaccine. Initial results from this study several weeks ago indicated this dose produced an adequate immunity. The new findings confirmed this, showing that the immune response 21 days after a single dose was as robust as the response 8-10 days after a second vaccine dose, Dr. Fauci said.

In another vaccine assessment, CDC researchers looked at results from four U.S. studies on the potential impact of vaccination with the seasonal flu vaccine on susceptibility to H1N1 infection. None of the four studies showed any change in the risk for H1N1 infection related to exposure to seasonal flu vaccine, Dr. Schuchat said.

Dr. Schuchat also reviewed the status of flu vaccine shipments. As of Oct. 8, 6.8 million doses of H1N1 vaccine were available from manufacturers for ordering and 3.7 million of these doses had been ordered by various state health departments. These numbers change daily, she added, and the CDC plans to release weekly updates on H1N1 vaccine supply and distribution.

The most recent data also show 77 million doses of seasonal flu vaccine shipped to U.S. locations, up by 7 million doses from the prior week. In response to a question about where seasonal flu vaccine doses go, Dr. Schuchat noted that the CDC controls only about 10% of the seasonal flu vaccine supply. “The good news is we have more seasonal flu vaccine out than we usually have at this time of year. The bad news is that more people want it,” which has led to some supply problems, she said.

Copyright (c) 2009 Elsevier Global Medical News. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

根据美国疾病控制与预防中心(CDC)10月3日收到的最新资料，大流行性甲型流感(H1N1)感染在10月初达到高峰。

 

9月27日至10月3日，在所有门诊病人中，流感样疾病病人占到5.1%，超过今年春季时H1N1活动水平，达到自2008年初季节性流感暴发以来的最高峰。在10月3日之前的一周，37个州有流感大规模流行，与此前一周相比增加了10个州。

 

CDC国家免疫接种与呼吸疾病中心主任Anne Schuchat博士在10月9日的新闻发布会上说，今年春季暴发流感的城市中，新增病例数并未出现下降。

 

CDC特别关注了美国的50个城市，发现有几个城市尽管2009年春季曾暴发流感，但目前流感病例数仍持续增加。该发现使人沮丧，否定了 原H1N1暴发社区的新增病例数会明显放缓的假设。Schuchat博士说，“我们还来不及确定是否会有第二波或第三波流感。”尽管今年春季流感暴发，但大多数人群仍对H1N1易感，她补充道。

 

近期的H1N1流感活动也使得18岁以下的儿童和青少年死亡例数增加。10月3日之前的一周，有19名儿童死于H1N1流感，使自该病毒出现的4月份以来的儿童死亡总数达到76例。约1/4的儿童没有基础疾病，尽管后期一些病例出现合并感染。Schuchat博士说，与此前3个流感季总计46~88名儿科死亡病例数相比，这意味着目前的死亡例数会超过以往。

 

发布会还通报了美国国家免疫与感染病研究所(NIAID)关于H1N1疫苗试验的最新进展。NIAID主任Anthony Fauci博士说，最重要的新发现是初步结果显示，同时注射H1N1流感疫苗和季节性流感疫苗对各自的保护作用没有影响。该结果来自于8月份进行的一项纳入400名健康成年人和400名健康老年人试验中的50人的数据。

 

他还通报了一项单剂、无佐剂、15µg注射型H1N1疫苗有效性研究的结果。该研究数周前公布的初步结果显示，该剂型可产生足够的免疫力。该发现证实，单剂注射21天后的免疫力与(两次注射的)第二针后8~10天产生的免疫力一样充分有效。

 

另一项对疫苗进行的评估中，CDC研究人员比较了4项在美国进行的注射季节性流感疫苗后对H1N1流感易感性的潜在影响的结果。Schuchat 博士说，4项研究均未发现注射季节性流感疫苗后感染H1N1风险的任何改变。

 

Schuchat博士还回顾了流感疫苗的物流配送情况。截止10月8日，有680万剂H1N1疫苗可供使用，其中的370万剂已被各州的卫生部门订购。数字每天还在变化，她补充说，CDC还将每周更新H1N1疫苗供应和配送的情况。

 

最新的资料显示，7,700万剂季节性流感疫苗已送往美国各地，与前一周比增加了700万剂。在回答季节性流感疫苗送往何处时，Schuchat博士说CDC只负责其中10%的供应。“好消息是我们今年比以往有更多的季节性流感疫苗，坏消息是有更多的人需要它，”这导致了一定程度的供给困难，Schuchat博士说。

 

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