HIV virological suppression influences response to the AS03‐adjuvanted monovalent pandemic influenza A H1N1 vaccine in HIV‐infected children

Design

Children with HIV are especially susceptible to complications from influenza infection, and effective vaccines are central to reducing disease burden in this population. We undertook a prospective, observational study to investigate the safety and immunogenicity of the inactivated split-virion AS03-adjuvanted pandemic H1N1(2009) vaccine in children with HIV.

Setting

National referral centre for Paediatric HIV in Ireland.

Sample

Twenty four children with HIV were recruited consecutively and received two doses of the vaccine. The serological response was measured before each vaccine dose (Day 0 and Day 28) and 2 months after the booster dose. Antibody titres were measured using a haemagglutination inhibition (HAI) assay. Seroprotection was defined as a HAI titre ≥ 1:40; seroconversion was defined as a ≥ fourfold increase in antibody titre and a postvaccination titre ≥ 1:40.

Main outcome measures

The seroconversion rates after prime and booster doses were 75% and 71%, respectively. HIV virological suppression at the time of immunization was associated with a significantly increased seroconversion rate (P = 0·009), magnitude of serological response (P = 0·02) and presence of seroprotective HAI titres (P = 0·017) two months after the booster dose. No other factor was significantly associated with the seroconversion/seroprotection rate. No serious adverse effects were reported. Vaccination had no impact on HIV disease progression. The AS03-adjuvanted pandemic H1N1 vaccine appears to be safe and immunogenic among HIV-infected children. A robust serological response appears to be optimized by adherence to a HAART regimen delivering virological suppression.     

An assessment of prime‐boost vaccination schedules with AS03A‐adjuvanted prepandemic H5N1 vaccines: a randomized study in European adults

Please cite this paper as: Gillard et al. (2012) An assessment of prime‐boost vaccination schedules with AS03_A‐adjuvanted prepandemic H5N1 vaccines: a randomized study in European adults. Influenza and Other Respiratory Viruses DOI: 10.1111/j.1750‐2659.2012.00349.x. Background Long‐term persistence of immune response and safety of an H5N1 prepandemic influenza vaccine adjuvanted with AS03 (an α‐tocopherol oil‐in‐water emulsion‐based adjuvant system) was evaluated using various prime‐boost schedules that mimicked potential pandemic scenarios (NCT00430521). Methods Five hundred and twelve healthy adults aged 18–60 years received primary vaccination with one or two doses (0, 21 days schedule) of the A/Vietnam/1194/2004 H5N1 vaccine followed by a booster dose (A/Vietnam/1194/2004 or A/Indonesia/05/2005 strain) six or twelve months later across eight randomized groups. Immunogenicity results by hemagglutination inhibition [HI] assay, microneutralization assay, and the cell‐mediated immune response (CMI) are reported here for the four groups boosted at Month 12. Results A one‐dose‐adjuvanted primary administration followed 12 months later by a single‐adjuvanted booster dose containing a heterologous vaccine strain met or exceeded all US and European criteria for both strains. Increasing the interval between the first and second dose (from 21 days to 12 months) resulted in stronger cross‐reactive immune responses against the A/Indonesia/05/2005 strain. The HI antibody response against the two strains persisted for 6 months after the booster dose irrespective of the booster vaccine’s strain. The neutralizing antibody responses and the CMI observed in the study population paralleled the HI immune response. Overall, the vaccine had a clinically acceptable safety profile. Conclusion The H5N1 vaccine in this study allowed for flexibility in the time interval between primary and booster vaccination and the use of a heterologous strain without impacting the strength of the humoral and cellular immune response to both vaccine strains.     

Phase II,randomized, open,controlled study of AS03‐adjuvanted H5N1 pre‐pandemic influenza vaccine in children aged 3 to 9 years: follow‐up of safety and immunogenicity persistence at 24 months post‐vaccination

Background

An AS03-adjuvanted H5N1 influenza vaccine elicited broad and persistent immune responses with an acceptable safety profile up to 6 months following the first vaccination in children aged 3–9 years.

Methods

In this follow-up of the Phase II study, we report immunogenicity persistence and safety at 24 months post-vaccination in children aged 3–9 years. The randomized, open-label study assessed two doses of H5N1 A/Vietnam/1194/2004 influenza vaccine (1·9 μg or 3·75 μg hemagglutinin antigen) formulated with AS03_A or AS03_B (11·89 mg or 5·93 mg tocopherol, respectively). Control groups received seasonal trivalent influenza vaccine. Safety was assessed prospectively and included potential immune-mediated diseases (pIMDs). Immunogenicity was assessed by hemagglutination-inhibition assay 12 and 24 months after vaccination; cross-reactivity and cell-mediated responses were also assessed. ({"type":"clinical-trial","attrs":{"text":"NCT00502593","term_id":"NCT00502593"}}NCT00502593).

Results

The safety population included 405 children. Over 24 months, five events fulfilled the criteria for pIMDs, of which four occurred in H5N1 vaccine recipients, including uveitis (n = 1) and autoimmune hepatitis (n = 1), which were considered to be vaccine-related. Overall, safety profiles of the vaccines were clinically acceptable. Humoral immune responses at 12 and 24 months were reduced versus those observed after the second dose of vaccine, although still within the range of those observed after the first dose. Persistence of cell-mediated immunity was strong, and CD4⁺ T cells with a T_H1 profile were observed.

Conclusions

Two doses of an AS03-adjuvanted H5N1 influenza vaccine in children showed low but persistent humoral immune responses and a strong persistence of cell-mediated immunity, with clinically acceptable safety profiles up to 24 months following first vaccination.     

Development of a new candidate H5N1 avian influenza virus for pre‐pandemic vaccine production

Background Highly pathogenic H5N1 avian influenza viruses currently circulating in birds have caused hundreds of human infections, and pose a significant pandemic threat. Vaccines are a major component of the public health preparedness for this likely event. The rapid evolution of H5N1 viruses has resulted in the emergence of multiple clades with distinct antigenic characteristics that require clade‐specific vaccines. A variant H5N1 virus termed clade 2.3.4 emerged in 2005 and has caused multiple fatal infections. Vaccine candidates that match the antigenic properties of variant viruses are necessary because inactivated influenza vaccines elicit strain‐specific protection. Objective To address the need for a suitable seed for manufacturing a clade 2.3.4 vaccine, we developed a new H5N1 pre‐pandemic candidate vaccine by reverse genetics and evaluated its safety and replication in vitro and in vivo. Methods A reassortant virus termed, Anhui/PR8, was produced by reverse genetics in compliance with WHO pandemic vaccine development guidelines and contains six genes from A/Puerto Rico/8/34 as well as the neuraminidase and hemagglutinin (HA) genomic segments from the A/Anhui/01/2005 virus. The multi‐basic cleavage site of HA was removed to reduce virulence. Results The reassortant Anhui/PR8 grows well in eggs and is avirulent to chicken and ferrets but retains the antigenicity of the parental A/Anhui/01/2005 virus. Conclusion These results indicate that the Anhui/PR8 reassortant lost a major virulent determinant and it is suitable for its use in vaccine manufacturing and as a reference vaccine virus against the H5N1 clade 2.3.4 viruses circulating in eastern China, Vietnam, Thailand, and Laos.     

A sensitive retroviral pseudotype assay for influenza H5N1‐neutralizing antibodies

Background The World Health Organisation (WHO) recommended the development of simple, safe, sensitive and specific neutralization assays for avian influenza antibodies. We have used retroviral pseudotypes bearing influenza H5 hemagglutinin (HA) as safe, surrogate viruses for influenza neutralization assays which can be carried out at Biosafety Level 2. Results Using our assay, sera from patients who had recovered from infection with influenza H5N1, and sera from animals experimentally immunized or infected with H5 tested positive for the presence of neutralizing antibodies to H5N1. Pseudotype neutralizing antibody titers were compared with titers obtained by hemagglutinin inhibition (HI) assays and microneutralization (MN) assays using live virus, and showed a high degree of correlation, sensitivity and specificity. Conclusions The pseudotype neutralization assay is as sensitive as horse erythrocyte HI and MN for the detection of antibodies to H5N1. It is safer, and can be applied in a high‐throughput format for human and animal surveillance and for the evaluation of vaccines.     

Ducks: The “Trojan Horses” of H5N1 influenza

Abstract Wild ducks are the main reservoir of influenza A viruses that can be transmitted to domestic poultry and mammals, including humans. Of the 16 hemagglutinin (HA) subtypes of influenza A viruses, only the H5 and H7 subtypes cause highly pathogenic (HP) influenza in the natural hosts. Several duck species are naturally resistant to HP Asian H5N1 influenza viruses. These duck species can shed and spread virus from both the respiratory and intestinal tracts while showing few or no disease signs. While the HP Asian H5N1 viruses are 100% lethal for chickens and other gallinaceous poultry, the absence of disease signs in some duck species has led to the concept that ducks are the “Trojan horses” of H5N1 in their surreptitious spread of virus. An important unresolved issue is whether the HP H5N1 viruses are maintained in the wild duck population of the world. Here, we review the ecology and pathobiology of ducks infected with influenza A viruses and ducks’ role in the maintenance and spread of HP H5N1 viruses. We also identify the key questions about the role of ducks that must be resolved in order to understand the emergence and control of pandemic influenza. It is generally accepted that wild duck species can spread HP H5N1 viruses, but there is insufficient evidence to show that ducks maintain these viruses and transfer them from one generation to the next.     

Efficacy of a heterologous vaccine and adjuvant in ferrets challenged with influenza virus H5N1

Please cite this paper as: Vela et al. (2012) Efficacy of a heterologous vaccine and adjuvant in ferrets challenged with influenza virus H5N1. Influenza and Other Respiratory Viruses 6(5), 328–340. Background In 1997, highly pathogenic avian influenza (HPAI) viruses caused outbreaks of disease in domestic poultry markets in Hong Kong. The virus has also been detected in infected poultry in Europe and Africa. Objective The objective of this study was to determine the efficacy of a heterologous vaccine administered with and without the aluminum hydroxide adjuvant in ferrets challenged with HPAI (A/Vietnam/1203/04). Methods Animals in four of the five groups were vaccinated twice 21 days apart, with two doses of a heterologous monovalent subvirion vaccine with or without an aluminum hydroxide adjuvant and challenged with a lethal target dose of A/Vietnam/1203/04. Results All animals vaccinated with the heterologous vaccine in combination with the aluminum hydroxide adjuvant survived a lethal challenge of A/Vietnam/1203/04. Four of the eight animals vaccinated with 30 μg of the vaccine without the adjuvant survived, while two of the eight animals vaccinated with 15 μg of the vaccine without the adjuvant survived. None of the unvaccinated control animals survived challenge. Additionally, changes in virus recovered from nasal washes and post‐mortem tissues and serology suggest vaccine efficacy. Conclusions Altogether, the data suggest that the heterologous vaccine in combination with the aluminum hydroxide adjuvant offers maximum protection against challenge with A/Vietnam/1203/04 when compared to the unvaccinated control animals or animals vaccinated without any adjuvant.     

Long‐term vaccine‐induced heterologous protection against H5N1 influenza viruses in the ferret model

Please cite this paper as: Ducatez et al. (2012) Long‐term vaccine‐induced heterologous protection against H5N1 influenza viruses in the ferret model. Influenza and Other Respiratory Viruses 7(4), 506–512. Background Highly pathogenic H5N1 influenza viruses reemerged in humans in 2003 and have caused fatal human infections in Asia and Africa as well as ongoing outbreaks in poultry. These viruses have evolved substantially and are now so antigenically varied that a single vaccine antigen may not protect against all circulating strains. Nevertheless, studies have shown that substantial cross‐reactivity can be achieved with H5N1 vaccines. These studies have not, however, addressed the issue of duration of such cross‐reactive protection. Objectives To directly address this using the ferret model, we used two recommended World Health Organization H5N1 vaccine seed strains – A/Vietnam/1203/04 (clade 1) and A/duck/Hunan/795/02 (clade 2.1) – seven single, double, or triple mutant viruses based on A/Vietnam/1203/04, and the ancestral viruses A and D, selected from sequences at nodes of the hemagglutinin and neuraminidase gene phylogenies to represent antigenically diverse progeny H5N1 subclades as vaccine antigens. Results All inactivated whole‐virus vaccines provided full protection against morbidity and mortality in ferrets challenged with the highly pathogenic H5N1 strain A/Vietnam/1203/04 5 months and 1 year after immunization. Conclusion If an H5N1 pandemic was to arise, and with the hypothesis that one can extrapolate the results from three doses of a whole‐virion vaccine in ferrets to the available split vaccines for use in humans, the population could be efficiently immunized with currently available H5N1 vaccines, while the homologous vaccine is under production.     

Live attenuated H5N1 vaccine with H9N2 internal genes protects chickens from infections by both Highly Pathogenic H5N1 and H9N2 Influenza Viruses

Please cite this paper as: Nang et al. (2013) Live attenuated H5N1 vaccine with H9N2 internal genes protects chickens from infections by both Highly Pathogenic H5N1 and H9N2 Influenza Viruses. Influenza and Other Respiratory Viruses 7(2) 120–131. Background The highly pathogenic H5N1 and H9N2 influenza viruses are endemic in many countries around the world and have caused considerable economic loss to the poultry industry. Objectives We aimed to study whether a live attenuated H5N1 vaccine comprising internal genes from a cold‐adapted H9N2 influenza virus could protect chickens from infection by both H5N1 and H9N2 viruses. Methods We developed a cold‐adapted H9N2 vaccine virus expressing hemagglutinin and neuraminidase derived from the highly pathogenic H5N1 influenza virus using reverse genetics. Results and Conclusions Chickens immunized with the vaccine were protected from lethal infections with homologous and heterologous H5N1 or H9N2 influenza viruses. Specific antibody against H5N1 virus was detected up to 11 weeks after vaccination (the endpoint of this study). In vaccinated chickens, IgA and IgG antibody subtypes were induced in lung and intestinal tissue, and CD4+ and CD8+ T lymphocytes expressing interferon‐gamma were induced in the splenocytes. These data suggest that a live attenuated H5N1 vaccine with cold‐adapted H9N2 internal genes can protect chickens from infection with H5N1 and H9N2 influenza viruses by eliciting humoral and cellular immunity.     

SERS-based immunomagnetic bead for rapid detection of H5N1 influenza virus

The surface-enhanced Raman scattering (SERS) has recently drawn attention in the detection of respiratory viruses, but there have been few reports of the direct detection of viruses. In this study, a sandwich immunomagnetic bead SERS was established for the rapid diagnosis of the H5N1 influenza virus. The detection limit was estimated to be 5.0 × 10⁻⁶ TCID₅₀/ml. The method showed excellent specificity with no cross-reaction with H1N1, H5N6 or H9N2. The H5N1 influenza virus detection accuracy of the SERS method was 100% in chicken embryos. The results hold great promise for the utilization of SERS as an innovative approach in the diagnosis of influenza virus.     

The mucosal and systemic immune responses elicited by a chitosan-adjuvanted intranasal influenza H5N1 vaccine

Please cite this paper as: Svindland et al. The mucosal and systemic immune responses elicited by a chitosan‐adjuvanted intranasal influenza H5N1 vaccine. Influenza and Other Respiratory Viruses DOI:10.1111/j.1750‐2659.2011.00271.x. Background Development of influenza vaccines that induce mucosal immunity has been highlighted by the World Health Organisation as a priority (Vaccine 2005;23:1529). Dose‐sparing strategies and an efficient mass‐vaccination regime will be paramount to reduce the morbidity and mortality of a future H5N1 pandemic. Objectives This study has investigated the immune response and the dose‐sparing potential of a chitosan‐adjuvanted intranasal H5N1 (RG‐14) subunit (SU) vaccine in a mouse model. Methods Groups of mice were intranasally immunised once or twice with a chitosan (5 mg/ml)‐adjuvanted SU vaccine [7·5, 15 or 30 μg haemagglutinin (HA)] or with a non‐adjuvanted SU vaccine (30 μg HA). For comparison, another group of mice were intranasally immunised with a whole H5N1 (RG‐14) virus (WV) vaccine (15 μg HA), and the control group consisted of unimmunised mice. Results The chitosan‐adjuvanted SU vaccine induced an immune response superior to that of the non‐adjuvanted SU vaccine. Compared with the non‐adjuvanted SU group, the chitosan‐adjuvanted SU vaccine elicited higher numbers of influenza‐specific antibody‐secreting cells (ASCs), higher concentrations of local and systemic antibodies and correspondingly an improved haemagglutination inhibition (HI) and single radial haemolysis (SRH) response against both the homologous vaccine strain and drifted H5 strains. We measured a mixed T‐helper 1/T‐helper 2 cytokine response in the chitosan‐adjuvanted SU groups, and these groups had an increased percentage of virus‐specific CD4⁺ T cells producing two Thelper 1 (Th1) cytokines simultaneously compared with the non‐adjuvanted SU group. Overall, the WV vaccine induced higher antibody concentrations in sera and an HI and SRH response similar to that of the chitosan‐adjuvanted SU vaccine. Furthermore, the WV vaccine formulation showed a stronger bias towards a T‐helper 1 profile than the SU vaccine and elicited the highest frequencies of CD4⁺ Th1 cells simultaneously secreting three different cytokines (INFγ⁺, IL2⁺ and INFα⁺). As expected, two immunisations gave a better immune response than one in all groups. The control group had very low or not detectable results in the performed immunoassays. Conclusion The cross‐clade serum reactivity, improved B‐ and T‐cell responses and dose‐sparing potential of chitosan show that a chitosan‐adjuvanted intranasal influenza vaccine is a promising candidate vaccine for further preclinical development.     

Comparative safety, immunogenicity, and efficacy of several anti-H5N1 influenza experimental vaccines in a mouse and chicken models (Testing of killed and live H5 vaccine)

Please cite this paper as: Gambaryan et al. (2011) Comparative safety, immunogenicity, and efficacy of several anti‐H5N1 influenza experimental vaccines in a mouse and chicken models. Parallel testing of killed and live H5 vaccine. Influenza and Other Respiratory Viruses 6(3), 188–195. Objective Parallel testing of inactivated (split and whole virion) and live vaccine was conducted to compare the immunogenicity and protective efficacy against homologous and heterosubtypic challenge by H5N1 highly pathogenic avian influenza virus. Method Four experimental live vaccines based on two H5N1 influenza virus strains were tested; two of them had hemagglutinin (HA) of A/Vietnam/1203/04 strain lacking the polybasic HA cleavage site, and two others had hemagglutinins from attenuated H5N1 virus A/Chicken/Kurgan/3/05, with amino acid substitutions of Asp54/Asn and Lys222/Thr in HA1 and Val48/Ile and Lys131/Thr in HA2 while maintaining the polybasic HA cleavage site. The neuraminidase and non‐glycoprotein genes of the experimental live vaccines were from H2N2 cold‐adapted master strain A/Leningrad/134/17/57 (VN‐Len and Ku‐Len) or from the apathogenic H6N2 virus A/Gull/Moscow/3100/2006 (VN‐Gull and Ku‐Gull). Inactivated H5N1 and H1N1 and live H1N1 vaccine were used for comparison. All vaccines were applied in a single dose. Safety, immunogenicity, and protectivity against the challenge with HPAI H5N1 virus A/Chicken/Kurgan/3/05 were estimated. Results All experimental live H5 vaccines tested were apathogenic as determined by weight loss and conferred more than 90% protection against lethal challenge with A/Chicken/Kurgan/3/05 infection. Inactivated H1N1 vaccine in mice offered no protection against challenge with H5N1 virus, while live cold‐adapted H1N1 vaccine reduced the mortality near to zero level. Conclusions The high yield, safety, and protectivity of VN‐Len and Ku‐Len made them promising strains for the production of inactivated and live vaccines against H5N1 viruses.     

H5N1禽流感病毒感染孕鼠的研究

目的用H5N1禽流感病毒感染昆明孕鼠,检测病毒在感染孕鼠各组织脏器中的复制及分布情况,并证明病毒能否通过孕鼠的胎盘垂直传染给胎鼠。方法用虎源H5N1亚型禽流感病毒滴鼻感染妊娠10-12 d的昆明孕鼠,观察孕鼠感染后的临床症状。接种病毒后第3、4、5、6和7 d分别处死3只孕鼠,取孕鼠的肺、脑、脾、肾、子宫、胎盘及胎鼠,利用RT-PCR、Real-time PCR和病毒分离方法检测各组织中的病毒核酸和病毒滴度,并进行病理组织学与免疫组织化学检测。结果昆明孕鼠接种病毒后第3 d,即可在肺、脑、脾、肾、子宫及胎盘组织中检测出H5N1禽流感病毒核酸,并从子宫、胎盘分离出H5N1禽流感病毒;感染后第6 d,从胎鼠体内检测到病毒核酸并分离出H5N1禽流感病毒。结论H5N1亚型禽流感病毒可以感染孕鼠,在孕鼠子宫和胎盘复制,感染后期可通过胎盘屏障传给胎鼠。     

Global epidemiology of human infections with highly pathogenic avian influenza A (H5N1) viruses

Abstract:   From 1997 through 2007, human infections with highly pathogenic avian influenza A (H5N1) viruses resulted in rare, sporadic, severe and fatal cases among persons in 14 countries in Asia, the Middle East, Eastern Europe and Africa. Of 369 reported human H5N1 cases that occurred from 1997 through 2007, overall mortality was 60%. Ten antigenically and genetically distinct clades of H5N1 viruses have been identified to date, and strains from four clades have infected humans. Surveillance has focused upon hospitalized cases of febrile acute lower respiratory tract disease among persons with exposure to sick or dead poultry, or to a human H5N1 case. Detection of H5N1 virus infection is based primarily upon collection of respiratory tract specimens from suspected cases for RT-PCR testing. Most human H5N1 cases were previously healthy children or young adults who developed severe acute pulmonary or multi-organ disease following direct or close contact with sick or dead H5N1 virus–infected poultry. Occasional clusters of H5N1 cases have occurred, predominantly among blood-related family members. Limited human-to-human H5N1 virus transmission has been reported or could not be excluded in some clusters. The frequency of asymptomatic or clinically mild H5N1 virus infection is unknown, but limited investigations suggest that such infections have been rare since 2003. There is no evidence of sustained human-to-human H5N1 virus spread. However, H5N1 viruses continue to circulate and evolve among poultry in many countries, and there are many unanswered questions about human infection with H5N1 viruses. Thus, the pandemic influenza threat presented by H5N1 viruses persists.     

Characterizing wild bird contact and seropositivity to highly pathogenic avian influenza A (H5N1) virus in Alaskan residents

Background

Highly pathogenic avian influenza A (HPAI) H5N1 viruses have infected poultry and wild birds on three continents with more than 600 reported human cases (59% mortality) since 2003. Wild aquatic birds are the natural reservoir for avian influenza A viruses, and migratory birds have been documented with HPAI H5N1 virus infection. Since 2005, clade 2.2 HPAI H5N1 viruses have spread from Asia to many countries.

Objectives

We conducted a cross-sectional seroepidemiological survey in Anchorage and western Alaska to identify possible behaviors associated with migratory bird exposure and measure seropositivity to HPAI H5N1.

Methods

We enrolled rural subsistence bird hunters and their families, urban sport hunters, wildlife biologists, and a comparison group without bird contact. We interviewed participants regarding their exposures to wild birds and collected blood to perform serologic testing for antibodies against a clade 2.2 HPAI H5N1 virus strain.

Results

Hunters and wildlife biologists reported exposures to wild migratory birds that may confer risk of infection with avian influenza A viruses, although none of the 916 participants had evidence of seropositivity to HPAI H5N1.

Conclusions

We characterized wild bird contact among Alaskans and behaviors that may influence risk of infection with avian influenza A viruses. Such knowledge can inform surveillance and risk communication surrounding HPAI H5N1 and other influenza viruses in a population with exposure to wild birds at a crossroads of intercontinental migratory flyways.     

A case of avian influenza A(H5N1) in England,January 2022

On 5 January 2022, high pathogenicity avian influenza A(H5N1) was confirmed in an individual who kept a large flock of ducks at their home in England. The individual remained asymptomatic. H5N1 was confirmed in 19/20 sampled live birds on 22 December 2021. Comprehensive contact tracing (n = 11) revealed no additional primary cases or secondary transmissions. Active surveillance of exposed individuals is essential for case identification. Asymptomatic swabbing helped refine public health risk assessment and facilitated case management given changes in avian influenza epidemiology.     

Review of clinical symptoms and spectrum in humans with influenza A/H5N1 infection

Abstract:   Influenza A/H5N1 infection has become the major emerging infectious disease of global concern again since late 2003. A history of exposure to dead or sick poultry or wild birds occurs in over 60% of cases of human H5N1 infection. The incubation period of avian-to-human transmission is generally between 2 and 5 days and the median duration of symptoms before hospitalization is about 4.5 days. The clinical spectrum has ranged from asymptomatic infection or mild influenza-like illness to severe pneumonia and multi-organ failure. Fever > 38°C, cough and dyspnoea are the major symptoms on presentation, whereas gastrointestinal symptoms such as watery diarrhoea, vomiting and abdominal pain are common early in the course of the disease. In contrast, upper respiratory tract symptoms are less prominent in human H5N1 infection when compared to seasonal influenza. Laboratory features of human H5N1 infection include leucopoenia, especially lymphopenia, elevated amino-transaminases, thrombocytopenia, prolonged prothrombin time and activated partial thromboplastin time, increased D-Dimer, increased serum lactate dehydrogenase and creatinine phospho-kinase, and hypoalbuminemia. A low absolute lymphocyte count on admission is associated with more severe disease and death. Radiographic abnormalities include multi-focal airspace consolidation, interstitial infiltrates, patchy or lobar involvement, with rapid progression to bilateral and diffuse ground-glass opacities consistent with ARDS. However, none of the clinical, laboratory and radiographic features are specific to H5N1 infection. A detailed exposure history needs to be elicited, including any close contact with sick or dead poultry, wild birds, other severely ill persons, travel to an area with A/H5N1 activity or work in laboratory handling samples possibly containing A/H5N1 virus.