Preexisting Antibody Response against 2009 Pandemic Influenza H1N1 Viruses in the Taiwanese Population

A novel pandemic influenza H1N1 (pH1N1) virus spread rapidly across the world in 2009. Due to the important role of antibody-mediated immunity in protection against influenza infection, we used an enzyme-linked immunosorbent assay-based microneutralization test to investigate cross-reactive neutralizing antibodies against the 2009 pH1N1 virus in 229 stored sera from donors born between 1917 and 2008 in Taiwan. The peak of cumulative geometric mean titers occurred in donors more than 90 years old and declined sharply with decreasing age. Sixteen of 27 subjects (59%) more than 80 years old had cross-reactive antibody titers of 160 or more against the 2009 pH1N1 virus, whereas none of the donors from age 9 to 49 had an antibody titer of 160 or more. Interestingly, 2 of 51 children (4%) from 6 months to 9 years old had an antibody titer of 40. We further tested the antibody responses in 9 of the 51 pediatric sera to three endemic seasonal influenza viruses isolated in 2006 and 2008 in Taiwan, and the results showed that only the 2 sera from children with antibody responses to the 2009 pH1N1 virus had high titers of neutralizing antibody against recent seasonal influenza virus strains. Our study shows the presence of some level of cross-reactive antibody in Taiwanese persons 50 years old or older, and the elderly subjects who may already have been exposed to the 1918 virus had high titers of neutralizing antibody to the 2009 pH1N1 virus. Our data also indicate that natural infection with the Taiwan 2006 and 2008 seasonal H1N1 viruses may induce a cross-reactive antibody response to the 2009 pH1N1 virus.Influenza A viruses have caused several pandemics during the past century and continue to cause epidemics around the world yearly. Pandemics are typically caused by the introduction of a virus with a hemagglutinin (HA) subtype that is new to human populations (14). In 2009, a novel pandemic influenza H1N1 (pH1N1) virus of swine origin spread rapidly and has caused variable disease globally via interhuman transmission (2, 3).The 2009 pH1N1 virus contains a unique combination of gene segments from both the North American and Eurasian swine lineages and is antigenically distinct from any known seasonal human influenza virus (14). Since H1N1 influenza A viruses have been circulating in human populations for decades, much of the world has encountered these viruses repeatedly, either through infection or through vaccination. Under the threat of a pandemic outbreak, however, a major concern is whether preexisting immunity can provide some protection from the novel 2009 pH1N1 virus.Recent reports from the United States suggested that 33% of individuals over the age of 60 years had neutralization antibodies to the novel 2009 pH1N1 virus, probably due to previous exposure to antigenically similar H1N1 viruses (1, 7). In Japan, however, appreciable neutralization antibodies against the 2009 pH1N1 virus were found only in individuals more than 90 years old (9). The differences in geographical location and vaccination programs against influenza in 1976 may account for the different age distributions of neutralization antibodies in the two countries. In the early 1900s, Taiwan had had a close relationship with Japan historically and geographically. The prevalence of influenza in Taiwan may be quite similar to that in Japan. In recent years, however, sequence analysis of epidemic influenza virus strains revealed that the Taiwanese strains usually circulate in Taiwan prior to their circulation in many other countries, including Japan. (16). The differences between the studies from United States and Japan, and the unique epidemic situation in Taiwan, highlight the need for us to assess the level of preexisting immunity in the Taiwanese population.In this study, we measured the titers of neutralizing antibodies against the 2009 pH1N1 virus in sera obtained from previous influenza infection or vaccination of different age groups. In addition, we also assessed the antibodies against the local seasonal H1N1 strains isolated in Taiwan in 2006 and 2008 (A/Taiwan/N86/06, A/Taiwan/N94/08, and A/Taiwan/N510/08) to evaluate whether there is a cross-reactive antibody response between recent local strains and the 2009 pH1N1 virus.     

Prevalence of antibodies against seasonal influenza A and B viruses in children in Netherlands

To gain insight into the age at which children become infected with influenza viruses for the first time, we analyzed the seroprevalence of antibodies against influenza viruses in children 0 to 7 years of age in the Netherlands. Serum samples were collected during a cross-sectional population-based study in 2006 and 2007 and were tested for the presence of antibodies against influenza A/H1N1, A/H3N2, and B viruses representative of viruses present in previous influenza seasons using the hemagglutination inhibition assay. The seroprevalence of antibodies to influenza virus was higher in children 1 to 6 months of age than in children 7 to 12 months of age, which likely reflects the presence of maternally derived antibodies. The proportion of study subjects >1 year of age with detectable antibodies against influenza viruses gradually increased with age until they reached the age of 6 years, when they all had antibodies to at least one influenza A virus. These findings may have implications for the development of vaccination strategies aiming at the protection of young children against seasonal and/or pandemic influenza virus infection.     

IgM,IgG, and IgA Antibody Responses to Influenza A(H1N1)pdm09 Hemagglutinin in Infected Persons during the First Wave of the 2009 Pandemic in the United States

The novel influenza A(H1N1)pdm09 virus caused an influenza pandemic in 2009. IgM, IgG, and IgA antibody responses to A(H1N1)pdm09 hemagglutinin (HA) following A(H1N1)pdm09 virus infection were analyzed to understand antibody isotype responses. Age-matched control sera collected from U.S. residents in 2007 and 2008 were used to establish baseline levels of cross-reactive antibodies. IgM responses often used as indicators of primary virus infection were mainly detected in young patient groups (≤5 years and 6 to 15 years old), not in older age groups, despite the genetic and antigenic differences between the HA of A(H1N1)pdm09 virus and pre-2009 seasonal H1N1 viruses. IgG and IgA responses to A(H1N1)pdm09 HA were detected in all age groups of infected persons. In persons 17 to 80 years old, paired acute- and convalescent-phase serum samples demonstrated ≥4-fold increases in the IgG and IgA responses to A(H1N1)pdm09 HA in 80% and 67% of A(H1N1)pdm09 virus-infected persons, respectively. The IgG antibody response to A(H1N1)pdm09 HA was cross-reactive with HAs from H1, H3, H5, and H13 subtypes, suggesting that infections with subtypes other than A(H1N1)pdm09 might result in false positives by enzyme-linked immunosorbent assay (ELISA). Lower sensitivity compared to hemagglutination inhibition and microneutralization assays and the detection of cross-reactive antibodies against homologous and heterologous subtype are major drawbacks for the application of ELISA in influenza serologic studies.     

Detection by microneutralization of antibodies against avian influenza virus in an endemic avian influenza region

Detection by microneutralization of low-titre antibodies (anti-H5 micro-NT titre ≤1 : 80) against avian influenza virus (H5N1) is usually taken to be a false-positive result. In this prospective study of 242 intensive-care unit patients admitted for severe community-acquired pneumonia, the prevalence of low-titre anti-H5 micro-NT was 2.4%. Prior exposure to poultry was the sole independent risk factor for these low-titre antibodies (adjusted OR 42.41; 95% CI 22.45–64.51; p <0.001). We suggest that low anti-H5 micro-NT titres be interpreted in conjunction with plausible poultry, environmental and human exposure to H5N1.     

A seroepidemiological study of pandemic A/H1N1(2009) influenza in a rural population of Mali

The swine-origin H1N1 influenza A virus (pH1N1(2009)) started to circulate worldwide in 2009, and cases were notified in a number of sub-Saharan African countries. However, no epidemiological data allowing estimation of the epidemic burden were available in this region, preventing comprehensive comparisons with other parts of the world. The CoPanFlu-Mali programme studied a cohort of 202 individuals living in the rural commune of Dioro (southern central Mali). Pre-pandemic and post-pandemic paired sera (sampled in 2006 and April 2010, respectively) were tested by the haemagglutination inhibition (HI) method. Different estimates of pH1N1(2009) infection during the 2009 first epidemic wave were used (increased prevalence of HI titre of ≥ 1/40 or ≥ 1/80, seroconversions) and provided convergent attack rate values (12.4-14.9%), the highest values being observed in the 0-19-year age group (16.0-18.4%). In all age groups, pre-pandemic HI titres of ≥1/40 were associated with complete absence of seroconversion; and geometric mean titres were <15 in individuals who seroconverted and >20 in others. Important variations in seroconversion rate existed among the different villages investigated. Despite limitations resulting from the size and composition of the sample analysed, this study provides strong evidence that the impact of the pH1N1(2009) first wave was more important than previously believed, and that the determinants of the epidemic spread in sub-Saharan populations were quite different from those observed in developed countries.     

2013~2018年天津市津南区0~14岁儿童季节性 甲型H1N1流感病原学监测分析

目的 分析2013~2018年天津市津南区季节性甲型H1N1流感流行情况,为科学预防和控制流感提供依据。方法 选择咸水沽医院作为监测哨点医院,采集2013年4月1日~2018年3月31日0~14岁儿童流感样病例（ILI）的咽拭子标本,采用实时荧光定量RT-PCR方法检测季节性甲型H1N1流感病毒核酸,以每年4月1日至次年3月31日为监测周期进行统计分析。结果 5个监测周期采集ILI 咽拭子标本分别为588、601、609、591和583份,季节性甲型H1N1流感病毒阳性率分别为9.69%、0、7.39%、10.15%和12.35%,阳性率比较,差异有统计学意义（P＜0.05）。5 个监测周期中有4个季节性甲型H1N1流感流行期,分别为2013年12月~2014年1月、2016年1~3月、2017年2~3月和2018年1~2月,2014年3月~2015年12月阳性病例数为0。按照年龄分为0~2岁、3~5岁、6~8岁、9~11岁和12~14岁5个年龄组,阳性率分别为3.15%、9.98%、11.08%、8.52%和5.98%,各年龄组之间阳性率比较,差异无统计学意义（P＞0.05）。不同性别人群的季节性甲型H1N1流感阳性率差异无统计学意义（P＞0.05）。结论 季节性甲型H1N1流感病毒呈现出季节性流行的特点,流行期一般在冬春季,高峰期出现在1月份左右,3~8岁年龄儿童阳性病例数量最多,为易感人群。为更好防控流感,及时掌握流行趋势,仍需加强监测。     

2009甲型H1N1流感大流行期间北京儿童的流感监测

目的 了解2009年甲型H1N1流感大流行期间北京地区儿童中流感流行的情况.方法 采用WHO推荐的实时荧光定量RT-PCR和国家流感中心推荐的分型方法,对2009年甲型H1N1流感大流行期间因流感样症状来首都儿科研究所附属儿童医院就诊患儿的咽拭子标本进行流感病毒核酸检测.结果 2009年6月1日至2010年2月28日期间共检测了4363份咽拭子标本,其中623例为甲型H1N1阳性,阳性率为14.3%,657例为其他甲型流感病毒阳性(15.1%),所有甲型流感病毒的总阳性率为29.3%.623例中有23例为危重症病例(占阳性患者的3.7%),其中5例死亡.618例信息完整的甲型H1N1病例中,患儿年龄为14天～16岁,性别比例为男比女为1.3:1.1～3岁儿童占25.2%,3～6岁学龄前儿童和6～12岁学龄儿童所占比例相近,各约占30%.在监测期间,仅呈现了一个甲型H1N1的流行波.2009年11月达到最高峰,随后减弱,2010年2月快速下降至2.7%.对监测期间每周20～30份临床标本同时进行季节性流感的监测显示,季节性H3N2、甲型H1N1和乙型流感交替流行.呼吸道合胞病毒(RSV)在甲型H1N1流行趋势减缓后逐渐流行成为流行优势株.结论 2009年6月至2010年2月北京地区儿童中出现甲型H1N1的流行,主要累及学龄前和学龄儿童.季节性流感和RSV与甲型H1N1交替流行.     

Differential diagnosis of pandemic (H1N1) 2009 infection by detection of haemagglutinin with an enzyme-linked immunoassay

A sensitive and convenient immunoassay that can directly differentiate pandemic (H1N1) 2009 (pH1N1) virus from seasonal influenza virus can play an important role in the clinic. In the presented study, a double-sandwich ELISA (pH1N1 ELISA), based on two monoclonal antibodies against haemagglutinin (HA) of the pH1N1 virus, was developed. After laboratory determination of the sensitivity and specificity characteristics, the performance of this assay was evaluated in a cohort of 904 patients with influenza-like illness. All seven strains of pH1N1 virus tested were positive by pH1N1 ELISA, with an average lower detection limit of 10^{3.0 ± 0.4} tissue culture infective dose (TCID)₅₀/mL (or 0.009 ± 0.005 HA titre). Cross-reaction of the assay with seasonal influenza virus and other common respiratory pathogens was rare. In pH1N1-infected patients, the sensitivity of the pH1N1 ELISA was 92.3% (84/91, 95% CI 84.8–96.9%), which is significantly higher than that of the BD Directigen EZ Flu A + B test (70.3%, p <0.01). The specificity of pH1N1 ELISA in seasonal influenza A patients was 100.0% (171/171, 95% CI 97.9–100.0%), similar to that in non-influenza A patients (640/642, 99.7%, 95% CI 98.9–100.0%). The positive predictive value for pH1N1 ELISA was 97.7% and the negative predictive value was 99.1% in this study population with a pH1N1 prevalence of 10.1%. In conclusion, detection of HA of pH1N1 virus by immunoassay appears to be a convenient and reliable method for the differential diagnosis of pH1N1 from other respiratory pathogens, including seasonal influenza virus.     

Evidence for Subclinical Influenza A(H1N1)pdm09 Virus Infection among Dogs in Guangdong Province,China

During 2012, we identified sampled dogs with elevated levels of antibodies (≥1:40) against A(H1N1)pdm09 virus by using a hemagglutination inhibition (HI) assay (seroprevalence, 24.7%) and a microneutralization (MN) assay (seroprevalence, 10.8%). These high seroprevalences of A(H1N1)pdm09 among dogs without clinical signs of influenza support the premise that dogs may play a role in the human influenza ecology in China.     

广东省深圳市流感流行特征分析

目的 掌握深圳市流感流行规律,了解甲流大流行以后流感的流行趋势.方法 对深圳市流感样病例监测数据、病原学检测结果和暴发疫情资料进行分析.结果 深圳市的流感样病例百分比(ILI％)为4.67％,呈逐年下降趋势,ILI年龄构成以0-4岁为主(占54.2％).流感病毒分离平均阳性率为10.6％,按月分析流感病毒分离阳性率与ILI％变化趋势呈正相关(r=0.447,P =0.001).全市报告了482起ILI暴发疫情,以乙型流感为主(占63.9％).2010年深圳市季节性流感出现了春季和夏季流行高峰,分别以乙型Victoria系和甲型H1N1亚型为优势株;2011年为冬春季和秋季高峰,以甲型H1N1和季节性H3亚型为优势株;2012年出现了冬春季和夏季高峰,以乙型(Victoria系和Yamagata系)和季节性H3亚型为优势株;2013年出现了春、秋、冬季三个流行高峰,分别以甲型H1N1、季节性H3和乙型Yamagata系为优势株.结论 深圳市季节性流感每年均出现2-3个流行高峰,分别在冬春季和夏秋季,每年流行高峰出现的时间不同,每年流行的型别不同.     

Seasonal H1N1 2007 influenza virus infection is associated with elevated pre‐exposure antibody titers to the 2009 pandemic influenza A (H1N1) virus

The new influenza strain detected in humans in April 2009 has caused the first influenza pandemic of the 21st century. A cross‐reactive antibody response, in which antibodies against seasonal H1N1 viruses neutralized the 2009 pandemic influenza A (H1N1) virus (2009 pH1N1), was detected among individuals aged >60 years. However, factors other than age associated with such a cross‐reactive antibody response are poorly documented. Our objective was to examine factors potentially associated with elevated pre‐exposure viro‐neutralization and hemagglutination‐inhibition antibody titers against the 2009 pH1N1. We also studied factors associated with antibody titers against the 2007 seasonal H1N1 virus. One hundred subjects participating in an influenza cohort were selected. Sera collected in 2008 were analysed using hemagglutination inhibition and viro‐neutralization assays for the 2009 pH1N1 virus and the 2007 seasonal H1N1 virus. Viro‐neutralization results were explored using a linear mixed‐effect model and hemagglutination‐inhibition results using linear‐regression models for interval‐censored data. Elevated antibody titers against 2009 pH1N1 were associated with seasonal 2007 H1N1 infection (viro‐neutralization, p 0.006; hemagglutination‐inhibition, p 0.018). Elevated antibody titers were also associated with age in the viro‐neutralization assay (p <0.0001). Seasonal 2007 H1N1 infection is an independent predictor of elevated pre‐exposure antibody titers against 2009 pH1N1 and may have contributed to lowering the burden of the 2009 pH1N1 pandemic.     

Seroprevalence to Influenza A(H1N1) 2009 Virus—Where Are We?

Age-specific seroprevalences for influenza virus make important contributions to estimating the burden of infection and determining the vulnerable populations. It is especially difficult to know the true clinical attack rates of the 2009 influenza A(H1N1) pandemic; however, we can estimate infection rates through analyses of seroprevalences based on national studies from different continents and countries with different demographics. After the 2009 influenza A(H1N1) pandemic, seroprevalence studies found 5 to 60% of populations across different continents and age groups having antibodies against the A(H1N1) 2009 virus. The seropositivity was highest in children and teenagers (20 to 60%) as well as in the elderly older than 80 years (20 to 40%). Preexisting cross-reactive antibodies against the virus were present mostly in sera of older people (born before 1950) who could have encountered viruses descended from the 1918 pandemic viruses. Experience with the 2009 pandemic indicates how essential early and timely serology data against the emerging virus can be for informing decisions on use of antivirals and vaccination campaigns, especially in regard to risk groups. The objectives of this review were to summarize the current data available on seroprevalence before and after the 2009 influenza A(H1N1) pandemic and the lessons learned for future pandemic preparedness.     

Sero‐immunity and serologic response to pandemic influenza A (H1N1) 2009 virus in Hong Kong

To study the serologic response to the new pandemic influenza A (H1N1) 2009 virus in Hong Kong, the level of immunity was measured before and after the occurrence of the outbreak, and the titer of antibody to the pandemic influenza A (H1N1) 2009 virus in serum samples of laboratory confirmed cases. The presence of pre‐outbreak pandemic influenza A (H1N1) 2009 virus antibodies in 37% of individuals older than >65 years suggested previous exposures to heterologous virus strains may have elicited cross‐reacting antibody. Following large outbreaks of pandemic influenza A 2009 virus that peaked in September 2009, there is a change in immunity level in various age groups consistent with the attack rates among population in Hong Kong. Among individuals with mild clinical presentation, the antibody response to pandemic influenza A (H1N1) 2009 virus was stronger in those individuals aged ≤24 years but took more time to reach a titer of 40 when compared with those aged >24 years; however, the antibody level declined slower among individuals aged ≤24 years. Regardless of age, the antibody response rose rapidly and reached much higher titer among individuals with severe clinical presentation. Further study is required to collect additional data on antibody persistence and determine how much protection is conferred by previous exposure to seasonal influenza A (H1N1) viruses. J. Med. Virol. 82:1809–1815, 2010. © 2010 Wiley‐Liss, Inc.     

Individual Antibody and T Cell Responses to Vaccination and Infection with the 2009 Pandemic Swine-Origin H1N1 Influenza Virus

Introduction  

The 2009 swine-origin H1N1 influenza virus (swH1N1) provided an opportunity to study immune responses to a new influenza strain in the context of seasonal influenza vaccination. Our goals were: to assess whether analyzing multiple parameters of immune responsiveness to influenza has an advantage over evaluating hemagglutination inhibition (HAI) titer alone, to determine whether vaccination with the seasonal vaccine induced cross-reactive immunity to swH1N1 in some individuals, and to determine whether the immune response against swH1N1 is higher after infection than vaccination.     

Immunogenicity, boostability, and sustainability of the immune response after vaccination against Influenza A virus (H1N1) 2009 in a healthy population

The emergence of a new influenza A virus (H1N1) variant in 2009 led to a worldwide vaccination program, which was prepared in a relatively short period of time. This study investigated the humoral immunity against this virus before and after vaccination with a 2009 influenza A virus (H1N1) monovalent MF59-adjuvanted vaccine, as well as the persistence of vaccine-induced antibodies. Our prospective longitudinal study included 498 health care workers (mean age, 43 years; median age, 44 years). Most (89%) had never or only occasionally received a seasonal influenza virus vaccine, and 11% were vaccinated annually (on average, for >10 years). Antibody titers were determined by a hemagglutination inhibition (HI) assay at baseline, 3 weeks after the first vaccination, and 5 weeks and 7 months after the second vaccination. Four hundred thirty-five persons received two doses of the 2009 vaccine. After the first dose, 79.5% developed a HI titer of ≥40. This percentage increased to 83.3% after the second dose. Persistent antibodies were found in 71.9% of the group that had not received annual vaccinations and in 43.8% of the group that had received annual vaccinations. The latter group tended to have lower HI titers (P=0.09). With increasing age, HI titers decreased significantly, by 2.4% per year. A single dose of the 2009 vaccine was immunogenic in almost 80% of the study population, whereas an additional dose resulted in significantly increased titers only in persons over 50. Finally, a reduced HI antibody response against the 2009 vaccine was found in adults who had previously received seasonal influenza virus vaccination. More studies on the effect of yearly seasonal influenza virus vaccination on the immune response are warranted.     

A novel H1N1 virus causes the first pandemic of the 21st century

A novel H1N1 virus of swine origin (H1N1v ) is currently spreading in humans, giving rise to the first pandemic in 40 years. The disease is of moderate severity but has notable differences from seasonal influenza. In contrast to seasonal influenza, those over 60 years are relatively spared, a likely consequence of the presence of H1N1v cross‐neutralizing antibody in this age group. Most patients appear to have mild influenza‐like illness and many of the complications leading to hospitalization and mortality occur in those with underlying disease conditions or pregnancy. Studies in animal models suggest that the novel H1N1v pandemic virus causes a more severe illness and appears to have a greater predilection for the alveolar epithelium than seasonal influenza viruses. As there are as yet little data on the pathogenesis and immunology of H1N1v infection in humans, we have reviewed relevant data from past pandemics, from seasonal influenza and avian influenza H5N1 to highlight key issues pertaining to pathogenesis and immunology.     

Pandemic and seasonal human influenza virus infections in domestic cats: prevalence, association with respiratory disease, and seasonality patterns

Domestic cats have several features that make them ideal vehicles for interspecies transmission of influenza viruses; however, they have been largely overlooked as potential reservoirs or bridging hosts. In this study, we conducted serological surveillance to assess the prevalence of novel pandemic H1N1 as well as seasonal human influenza virus infections in domestic cats in Ohio. Four hundred serum samples collected from domestic cats (September 2009 to September 2010) were tested using a hemagglutination inhibition (HI) test. The seroprevalences of pandemic H1N1, seasonal H1N1, and H3N2 were 22.5%, 33%, and 43.5%, respectively. In addition, a significant association between clinical feline respiratory disease and influenza virus infection was documented. In this sample of cats, the prevalence of pandemic H1N1 did not follow the seasonality pattern of seasonal H1N1 or H3N2 influenza, similar to observations in humans. Pandemic H1N1 seroprevalence did not vary in relation to ambient temperature changes, while the seroprevalence of seasonal H3N2 and H1N1 influenza viruses increased with the decline of ambient temperature. Our results highlight the high prevalence of influenza virus infection in domestic cats, a seasonality pattern of influenza virus infection comparable to that in humans, and an association of infection with clinical respiratory disease.     

无锡市流感病毒抗体水平调查

目的调查无锡市人群中甲型、乙型流感病毒抗体水平和新甲型H1N1流感病毒传人前后人群中抗体水平,并对新甲型H1N1流感病毒传人1年后自然人群中成人抗体水平与接种新甲型H1N1流感疫苗后1年的成人抗体水平进行比较。方法收集2008年9月至2009年5月、2010年9月至2011年1月无锡市不同年龄段人群血清和接种新甲型HIN1流感疫苗1年的成人血清,用血凝抑制（HI）试验测定抗体,并比较不同时间段各人群中的流感抗体阳性率、保护率和几何平均滴度（GMT）。结果新甲型H1N1流感病毒传入前,无锡市自然人群的HI抗体阳性率为2．86％（4／140）,保护率为0．71％（1／140）,GMT为5．23。新甲型H1N1流感病毒传入1年后,自然人群的HI抗体阳性率为66．33％,保护率为37．76％、GMT为19．17;其中成人HI抗体阳性率、保护率和GMT分别为50．00％、19．44％和13．09。接种新甲型H1N1流感疫苗的成人1年后HI抗体阳性率、保护率和GMT分别为61．36％、22．73％和14．14,与自然人群中成人在流感病毒传入1年后的抗体水平差异无统计学意义（P均〉0．05）。无锡市人群中甲型与乙型流感病毒HI抗体水平分别为：H1N1病毒抗体阳性率为55．00％,保护率为35．00％,GMT16．90;H3N2抗体阳性率为86．40％,保护率为84．30％,GMT为58．56。结论新甲型H1N1流感病毒传入无锡市1年后,自然人群中新甲型H1N1流感病毒抗体阳性率、保护率和GMT均已达到季节性流感抗体水平。同时人群中已有一定水平的甲型、乙型流感病毒抗体,近期不会发生较大的季节性流感疫情。     

Serological report of pandemic and seasonal human influenza virus infection in dogs in southern China

From January to July 2012, we looked for evidence of subclinical A (H1N1) pdm09 and seasonal human influenza viruses infections in healthy dogs in China. Sera from a total of 1920 dogs were collected from Guangdong, Guangxi, Fujian and Jiangxi provinces. We also examined archived sera from 66 dogs and cats that were collected during 2008 from these provinces. Using hemagglutination inhibition (HI) and microneutralization (MN) assays, we found that only the dogs sampled in 2012 had elevated antibodies (≥1:32) against A(H1N1)pdm09 virus and seasonal human influenza viruses: Of the 1920 dog sera, 20.5 % (n = 393) had elevated antibodies against influenza A(H1N1) pdm09 by the HI assay, 1.1 % (n = 22), and 4.7 % (n = 91) of the 1920 dogs sera had elevated antibodies against human seasonal H1N1 influenza virus and human seasonal H3N2 influenza virus by the HI assay. Compared with dogs that were raised on farms, dogs that were raised as pets were more likely to have elevated antibodies against A(H1N1)pdm09 and seasonal human influenza viruses. Seropositivity was highest among pet dogs, which likely had more diverse and frequent exposures to humans than farm dogs. These findings will help us better understand which influenza A viruses are present in dogs and will contribute to the prevention and control of influenza A virus. Moreover, further in-depth study is necessary for us to understand what roles dogs play in the ecology of influenza A.     

Immune responses to infection with H5N1 influenza virus

Influenza A H5N1 viruses remain a substantial threat to global public health. In particular, the expanding genetic diversity of H5N1 viruses and the associated risk for human adaptation underscore the importance of better understanding host immune responses that may protect against disease or infection. Although much emphasis has been placed on investigating early virus–host interactions and the induction of innate immune responses, little is known of the consequent adaptive immune response to H5N1 virus infection. In this review, we describe the H5N1 virus-specific and cross-reactive antibody and T cell responses in humans and animal models. Data from limited studies suggest that although initially robust, there is substantial waning of the serum antibody responses in survivors of H5N1 virus infection. Characterization of monoclonal antibodies generated from memory B cells of survivors of H5N1 virus infection has provided an understanding of the fine specificity of the human antibody response to H5N1 virus infection and identified strategies for immunotherapy. Human T cell responses induced by infection with seasonal influenza viruses are directed to relatively conserved internal proteins and cross-react with the H5N1 subtype. A role for T cell-based heterosubtypic immunity against H5N1 viruses is suggested in animal studies. Further studies on adaptive immune responses to H5N1 virus infection in both humans and animals are needed to inform the design of optimal immunological treatment and prevention modalities.