Circulating Influenza Strains Research Articles

Influenza in Canada, 2012-2013 season.

This report summarizes influenza activity in Canada during the 2012-13 influenza season (August 26, 2012-August 24, 2013) from data obtained through the FluWatch surveillance program. FluWatch collected information from six primary indicators of influenza activity that describe the epidemiologic and virologic behaviour of influenza in Canada: sentinel laboratory-based influenza detections; strain characterization and antiviral resistance for circulating influenza viruses; primary care consultation rates of influenza-like illness; regional influenza activity levels; influenza-associated severe outcomes; and pharmacy surveillance. The influenza season peaked nationally between late December 2012 and early January 2013 with influenza A(H3N2) identified as the predominant circulating influenza strain until early March, when influenza B became the predominant circulating strain. The cumulative reported hospitalization rates for all age groups were 25.0 per 100,000. Influenza A most greatly affected adults ≥65 years of age and influenza B most greatly affected children ≤19 years of age. The influenza season was moderately severe. When compared to the previous two seasons, which were considered relatively mild, there was a significant increase in laboratory detections for influenza, as well as hospitalizations associated with influenza in 2012-13.

Virus-vectored influenza virus vaccines.

Despite the availability of an inactivated vaccine that has been licensed for >50 years, the influenza virus continues to cause morbidity and mortality worldwide. Constant evolution of circulating influenza virus strains and the emergence of new strains diminishes the effectiveness of annual vaccines that rely on a match with circulating influenza strains. Thus, there is a continued need for new, efficacious vaccines conferring cross-clade protection to avoid the need for biannual reformulation of seasonal influenza vaccines. Recombinant virus-vectored vaccines are an appealing alternative to classical inactivated vaccines because virus vectors enable native expression of influenza antigens, even from virulent influenza viruses, while expressed in the context of the vector that can improve immunogenicity. In addition, a vectored vaccine often enables delivery of the vaccine to sites of inductive immunity such as the respiratory tract enabling protection from influenza virus infection. Moreover, the ability to readily manipulate virus vectors to produce novel influenza vaccines may provide the quickest path toward a universal vaccine protecting against all influenza viruses. This review will discuss experimental virus-vectored vaccines for use in humans, comparing them to licensed vaccines and the hurdles faced for licensure of these next-generation influenza virus vaccines.

Higher vaccine effectiveness in seasons with predominant circulation of seasonal influenza A(H1N1) than in A(H3N2) seasons: Test-negative case-control studies using surveillance data, Spain, 2003-2011

BackgroundWe used data provided by the Spanish influenza surveillance system to measure seasonal influenza vaccine effectiveness (VE) against medically attended cases, laboratory confirmed with the predominately circulating influenza virus over eight seasons (2003–2011). MethodsUsing the test-negative case-control design, we compared the vaccination status of swabbed influenza-like illnesses (ILI) patients who were laboratory confirmed with predominantly circulating influenza strain in the season (cases) to that of ILI patients testing negative for any influenza (controls). Data on age, sex, vaccination status and laboratory results were available for all seasons. We used logistic regression to calculate adjusted influenza VE for age, week of swabbing, Spanish region and season. We calculated the influenza VE by each season and pooling the seasons with the same predominant type/subtype. ResultsOverall influenza VE against infection with A(H3N2) subtype (four seasons) was 31 (95% confidence interval (CI):10; 48). For seasonal influenza A(H1N1) (two seasons), the effectiveness was 86% (95% CI: 65; 94). Against B infection (three seasons), influenza VE was 47% (95% CI: 27; 62). ConclusionsThe Spanish influenza surveillance system allowed estimating influenza VE in the studied seasons for the predominant strain. Strengthening the influenza surveillance will result in more precise VE estimates for decision making.

Performance of eHealth data sources in local influenza surveillance: a 5-year open cohort study.

BackgroundThere is abundant global interest in using syndromic data from population-wide health information systems—referred to as eHealth resources—to improve infectious disease surveillance. Recently, the necessity for these systems to achieve two potentially conflicting requirements has been emphasized. First, they must be evidence-based; second, they must be adjusted for the diversity of populations, lifestyles, and environments.ObjectiveThe primary objective was to examine correlations between data from Google Flu Trends (GFT), computer-supported telenursing centers, health service websites, and influenza case rates during seasonal and pandemic influenza outbreaks. The secondary objective was to investigate associations between eHealth data, media coverage, and the interaction between circulating influenza strain(s) and the age-related population immunity.MethodsAn open cohort design was used for a five-year study in a Swedish county (population 427,000). Syndromic eHealth data were collected from GFT, telenursing call centers, and local health service website visits at page level. Data on mass media coverage of influenza was collected from the major regional newspaper. The performance of eHealth data in surveillance was measured by correlation effect size and time lag to clinically diagnosed influenza cases.ResultsLocal media coverage data and influenza case rates showed correlations with large effect sizes only for the influenza A (A) pH1N1 outbreak in 2009 (r=.74, 95% CI .42-.90; P<.001) and the severe seasonal A H3N2 outbreak in 2011-2012 (r=.79, 95% CI .42-.93; P=.001), with media coverage preceding case rates with one week. Correlations between GFT and influenza case data showed large effect sizes for all outbreaks, the largest being the seasonal A H3N2 outbreak in 2008-2009 (r=.96, 95% CI .88-.99; P<.001). The preceding time lag decreased from two weeks during the first outbreaks to one week from the 2009 A pH1N1 pandemic. Telenursing data and influenza case data showed correlations with large effect sizes for all outbreaks after the seasonal B and A H1 outbreak in 2007-2008, with a time lag decreasing from two weeks for the seasonal A H3N2 outbreak in 2008-2009 (r=.95, 95% CI .82-.98; P<.001) to none for the A p H1N1 outbreak in 2009 (r=.84, 95% CI .62-.94; P<.001). Large effect sizes were also observed between website visits and influenza case data.ConclusionsCorrelations between the eHealth data and influenza case rates in a Swedish county showed large effect sizes throughout a five-year period, while the time lag between signals in eHealth data and influenza rates changed. Further research is needed on analytic methods for adjusting eHealth surveillance systems to shifts in media coverage and to variations in age-group related immunity between virus strains. The results can be used to inform the development of alert-generating eHealth surveillance systems that can be subject for prospective evaluations in routine public health practice.

Rapid production of synthetic influenza vaccines.

The strain composition of influenza vaccines must be changed regularly to track influenza virus antigenic evolution. During outbreaks with pandemic potential, strain changes are urgent. The systems for accomplishing vaccine strain changes have required the shipment of viruses and other biological materials around the globe, with delays in vaccine availability, and have used legacy techniques of egg-based virus cultivation, resulting in vaccine mismatches. In collaboration with Synthetic Genomics Vaccines Inc. and the US Biomedical Advanced Research and Development Authority, Novartis has developed a synthetic approach to influenza vaccine virus generation. Synthetic influenza vaccine viruses and mammalian cell culture technology promise influenza vaccines that match circulating influenza strains more closely and are delivered in greater quantities, more rapidly than vaccines produced by conventional technologies. These new technologies could yield an improved influenza vaccine response system in which viral sequence data from many sources are posted on the Internet, are downloaded by vaccine manufacturers, and are used to rescue multiple, attenuated vaccine viruses directly on high yielding backbones. Elements of this system were deployed in the response to the 2013 H7N9 influenza outbreak in China. The result was the production, clinical testing, and stockpiling of an H7N9 vaccine before the second wave of the outbreak struck at the end of 2013. Future directions in synthetic influenza vaccine technology include the automation of influenza virus rescue from sequence data and the merger of synthetic and self-amplifying mRNA vaccine technologies. The result could be a more robust and effective influenza vaccine system.

Effectiveness of seasonal influenza vaccine in preventing medically attended influenza infection in England and Wales during the 2010/2011 season: a primary care-based cohort study

Estimates of seasonal influenza vaccine effectiveness (VE) are affected by factors such as the strain of the current circulating influenza virus and characteristics of the host. The objective of this study was to provide VE estimates for the 2010/2011 seasonal trivalent influenza vaccine (TIV) in preventing medically attended influenza in England and Wales for the season 2010/2011. A cohort study design was employed using electronic health records extracted from 104 GP practices in the Royal College of General Practitioners (RCGP) primary care sentinel network. Endpoints included influenza-like illness (ILI), lower respiratory tract infection (LTRI) as well as PCR-confirmed influenza from patients swabbed from practices participating in a swabbing scheme. Adjustment was made for age, month, underlying chronic condition, region and number of consultations in the 12months prior to the study period. In addition to the cohort analysis, a nested test-negative case-control analysis (TNCC) was carried out using the swab-negative results as controls. In the cohort analysis, VE against LRTI was -0·5% [95% CI: (-7·0%, 7·5%)], against ILI was 37·8% [95% CI: (32·3%, 43·0%)] and against PCR-confirmed influenza was 50·0% [95% CI:(25·9%, 65·6%)] for type A and 44·4% [95% CI: (10·1%, 65·6%)] for type B. Using the TNCC design, the type A VE was 56·5% [95% CI: (30·4%, 72·7%)] and for type B was 54·0% [95% CI: (21·0%, 73·3%)]. This study shows that the 2010/2011 TIV provided moderate protection against the circulating influenza strains for the 2010/2011 season. It also suggests that VE against the less specific diagnosis of ILI can be found, but less specific endpoints such as LRTI are not useful.

Evaluation of Three Influenza Neuraminidase Inhibition Assays for Use in a Public Health Laboratory Setting during the 2011–2012 Influenza Season

We evaluated the implementation of three commercially available neuraminidase inhibition assays in a public health laboratory (PHL) setting. We also described the drug susceptibility patterns of human influenza A and B circulating in Maryland during the 2011-2012 influenza season. From January to May 2012, 169 influenza virus isolates were tested for phenotypic susceptibility to oseltamivir, zanamivir, and peramivir using NA-Fluor(TM), NA-Star®, and NA-XTD(TM) concurrently. A 50% neuraminidase inhibitory concentration (IC50) value was calculated to determine drug susceptibility. We used the standard deviation based on the median absolute deviation of the median analysis to determine the potential for reduced drug susceptibility. We evaluated each assay for the use of resources in high- and low-volume testing scenarios. One of the 25 2009 influenza A (H1N1) pandemic isolates tested was resistant to oseltamivir and peramivir, and sensitive to zanamivir, on all three platforms. Eighty-two influenza A (H3N2) and 62 B isolates were sensitive to all three drugs in all three assays. For a low-volume scenario, NA-Star and NA-XTD took 120 minutes to complete, while NA-Fluor required 300 minutes to complete. The lowest relative cost favored NA-Star. In a high-volume scenario, NA-Fluor had the highest throughput. Reagent use was most efficient when maximizing throughput. Cost efficiency from low- to high-volume testing improved the most for NA-Star. Our evaluation showed that both chemiluminescent and fluorescent neuraminidase inhibition assays can be successfully implemented in a PHL setting to screen circulating influenza strains for neuraminidase inhibitor resistance. For improved PHL influenza surveillance, it may be essential to develop guidelines for phenotypic drug-resistance testing that take into consideration a PHL's workload and available resources.

Comparing Influenza Positivity Rates by Real-Time RT-PCR, Elisa and Viral Culture Methods in Côte D'Ivoire, West Africa, in 2009.

Detection of circulating influenza strains is a key public health concern especially in limited-resource settings where diagnosis capabilities remain a challenge. As part of multi-site surveillance in Côte d'Ivoire during the 2009 influenza A(H1N1) pandemic, we had the opportunity to test respiratory specimens collected from patients with acute respiratory illness (ARI). We analyzed and compared the percentage of specimens testing positive using three laboratory methods (rtRT-PCR, ELISA, viral culture). From January to October 2009, 1,356 respiratory specimens were collected from patients with acute respiratory illness and shipped at the WHO NIC (Institut Pasteur) Cote d'Ivoire, and 453 (33%) tested positive for influenza by one or more laboratory methods. The proportion of positive influenza tests did not differ by the sex or age of the patient or presenting symptoms, but did differ depending on the timing and site of specimen collection. Of the 453 positive specimens, 424 (93.6%) were detected by PCR, 199 (43.9%) by ELISA and 40 (8.8%) by viral culture. While seasonal influenza A(H1N1) virus strains were prominent, only four 2009 pandemic influenza A(H1N1) cases were detected. Use of molecular biology method (rtRT-PCR) increased sensitivity and diagnosis capabilities. Among all three methods used, rRT-PCR was the most sensitive and rapid method. More capacity building is still required for viral culture. Need to collect denominator data in order to have an accurate estimate of the burden of influenza. There was delayed introduction of pandemic influenza A(H1N1)2009 in Cote d'Ivoire.

Mid-season influenza vaccine effectiveness 2011–2012: A Department of Defense Global, Laboratory-based, Influenza Surveillance System case–control study estimate

Mid-season influenza vaccine effectiveness (VE) was estimated using data from surveillance conducted by the Department of Defense Global, Laboratory-based, Influenza Surveillance Program at the United States Air Force School of Aerospace Medicine. Respiratory specimens from geographically diverse military members and dependents who sought medical care 2 October 2011–3 March 2012 were analyzed by viral culture and real-time reverse transcriptase-polymerase chain reaction; influenza viruses were typed and sequenced. Controls were influenza test-negative. Overall, vaccine type and subtype-specific VE were estimated using logistic regression. Adjusted VE (95% confidence interval) was: overall 77 (57–87)%; live attenuated vaccine (LAIV) 74 (48–87)%; trivalent inactivated vaccine (TIV) 75 (48–88)%. H3 component-specific VE was: overall 77 (52–89)%; LAIV 78 (47–91)%; TIV 74 (38–89)%; data were insufficient for separate H1 and B estimates. Both vaccine types showed moderate to high VE, indicating significant protection against circulating influenza strains.

Recrudescent Wave of A/H1N1pdm09 Influenza Viruses in Winter 2012-2013 in Kashmir, India.

Some parts of world, including India observed a recrudescent wave of influenza A/H1N1pdm09 in 2012. We undertook a study to examine the circulating influenza strains, their clinical association and antigenic characteristics to understand the recrudescent wave of A/H1N1pdm09 from November 26, 2012 to Feb 28, 2013 in Kashmir, India. Of the 751 patients (545 outpatient and 206 hospitalized) presenting with acute respiratory infection at a tertiary care hospital in Srinagar; 184 (24.5%) tested positive for influenza. Further type and subtype analysis revealed that 106 (58%) were influenza A (H1N1pdm09 =105, H3N2=1) and 78 (42%) were influenza B. The influenza positive cases had a higher frequency of chills, nasal discharge, sore throat, body aches and headache, compared to influenza negative cases. Of the 206 patients hospitalized for pneumonia/acute respiratory distress syndrome or an exacerbation of an underlying lung disease, 34 (16.5%) tested positive for influenza (22 for H1N1pdm09, 11 for influenza B). All influenza-positive patients received oseltamivir and while most patients responded well to antiviral therapy and supportive care, 6 patients (4 with H1N1pdm09 and 2 with influenza B) patients died of progressive respiratory failure and multi-organ dysfunction. Following a period of minimal circulation, H1N1pdm09 re-emerged in Kashmir in 2012-2013, causing serious illness and fatalities. As such the healthcare administrators and policy planners need to be wary and monitor the situation closely.

Effect of influenza vaccines against mismatched strains: a systematic review protocol

BackgroundInfluenza vaccines are most effective when the antigens in the vaccine match those of circulating influenza strains. The extent to which the vaccine is protective when circulating strains differ from vaccine antigens, or are mismatched, is uncertain. We propose to systematically review the cross-protection offered by influenza vaccines against circulating influenza A or B viruses that are not antigenically well-matched to vaccine strains.Methods/DesignThis is a protocol for a systematic review and meta-analysis. Placebo-controlled randomized clinical trials (RCTs) reporting laboratory-confirmed influenza among healthy participants vaccinated with antigens of influenza strains that differed from those circulating will be included. The primary outcome is the incidence of laboratory-confirmed influenza (polymerase chain reaction (PCR) or viral culture). The secondary outcome is the incidence of laboratory-confirmed influenza through antibody assay (a less sensitive test than PCR or viral culture) alone or combined with PCR, and/ or viral culture. The review will be limited to RCTs written in English.We will search MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials, previous influenza reviews, and the reference lists of included studies to identify potentially relevant RCTs. Two independent reviewers will conduct all levels of screening, data abstraction, and quality appraisal (using the Cochrane risk of bias tool).If appropriate, random effects meta-analysis of vaccine efficacy will be conducted in SAS (version 9.2) by calculating the relative risk. Vaccine efficacy will be calculated using the following formula: (1 - relative risk × 100). The results will be analyzed by type of vaccine (live attenuated, trivalent inactivated, or other). Subgroup analysis will include the effects of age (children, adults, older participants), and influenza A versus influenza B on the results. For influenza B we will also consider variable degrees of antigenic mismatch (lineage and drift mismatch).DiscussionOur results can be used by researchers and policy-makers to help predict the efficacy of influenza vaccines during mismatched influenza seasons. Furthermore, the review will be of interest to patients and clinicians to determine whether to get immunized or support immunization for a particular influenza season.

Modifying the thermostability of inactivated influenza vaccines

BackgroundRespiratory infections caused by influenza viruses spread rapidly, resulting in significant annual morbidity and mortality worldwide. Currently, the most effective public health measure against infection is immunisation with an influenza vaccine matching the relevant circulating influenza strains. Although a number of developments in terms of influenza vaccine production, safety and immunogenicity have been reported, limitations in our understanding of vaccine stability still exist. In this report we seek to identify compounds that increase influenza vaccine thermostability. MethodsWe use plaque inhibition on confluent MDCK cells to identify compounds which inhibit the entry of various seed strain viruses. The effect of these compounds on vaccine thermal lability is evaluated through SRID analysis. The significance of these results is tested by a two-way analysis of variance (ANOVA) method. ResultsWe identify two compounds which selectively inhibit entry of different group I or group II influenza strains through prevention of the neutral-pH to low-pH conformational change of hemagglutinin. Compounds which were able to inhibit virus entry were also able to limit thermally induced potency loss in matched influenza vaccines. Furthermore, we demonstrate that this effect is independent of product formulation or the presence of multiple HA types. ConclusionsThis work provides further evidence for a link between HA conformational stability in the virus and thermostability of the corresponding vaccine preparation. It also suggests straightforward approaches to improve the stability and predictability of influenza vaccine preparations.

Prevention of Mortality and Pneumonia Among Nursing Home Older Adults by Dual Pneumococcal and Seasonal Influenza Vaccination During a Pandemic Caused by Novel Pandemic Influenza A (H1N1)

To evaluate the efficacy of dual vaccination of seasonal influenza and pneumococcus in nursing home older adults during a novel pandemic of influenza A (H1N1). Nine nursing homes in Hong Kong. A total of 532 nursing home older adults were included in the study. Efficacy of dual vaccination of seasonal influenza and pneumococcus in nursing home older adults during a novel pandemic influenza A (H1N1). A prospective 12-month cohort study was conducted on older residents from December 2009 to November 2010. Participants were divided into 3 groups according to their choice of vaccination: received both seasonal influenza and 23-valent pneumococcal polysaccharide vaccine (PPV-TIV group), received seasonal influenza vaccine alone (TIV group), and those who refused both vaccinations (unvaccinated group). Those who had received vaccination for influenza A (H1N1) were excluded. Outcome measures included mortality from all causes, pneumonia, and vascular causes. There were 246 in the PPV-TIV group, 211 in the TIV group, and 75 in the unvaccinated group. Baseline characteristics were similar among the groups. The 12-month mortality rates of the PPV-TIV, TIV alone group, and unvaccinated group were 17.1%, 27.0%, and 37.3% respectively (P < .001). Multivariate analysis demonstrated that, compared with vaccination of seasonal influenza alone, dual vaccination significantly reduced all-cause mortality (hazard ratio [HR] 0.54; 95% confidence interval [CI]: 0.35-0.84; P < .01), mortality from pneumonia (HR 0.60; 95% CI: 0.35-0.99; P < .05), and mortality from vascular causes (HR 0.24; 95% CI: 0.09-0.64; P < .01). During an influenza pandemic or when the circulating influenza strain was not matched by the trivalent seasonal influenza vaccine, dual vaccination of influenza and pneumococcus provided additional protection to nursing home older adults in reducing mortality.

Interleukin-6 Is a Potential Biomarker for Severe Pandemic H1N1 Influenza A Infection

Pandemic H1N1 influenza A (H1N1pdm) is currently a dominant circulating influenza strain worldwide. Severe cases of H1N1pdm infection are characterized by prolonged activation of the immune response, yet the specific role of inflammatory mediators in disease is poorly understood. The inflammatory cytokine IL-6 has been implicated in both seasonal and severe pandemic H1N1 influenza A (H1N1pdm) infection. Here, we investigated the role of IL-6 in severe H1N1pdm infection. We found IL-6 to be an important feature of the host response in both humans and mice infected with H1N1pdm. Elevated levels of IL-6 were associated with severe disease in patients hospitalized with H1N1pdm infection. Notably, serum IL-6 levels associated strongly with the requirement of critical care admission and were predictive of fatal outcome. In C57BL/6J, BALB/cJ, and B6129SF2/J mice, infection with A/Mexico/4108/2009 (H1N1pdm) consistently triggered severe disease and increased IL-6 levels in both lung and serum. Furthermore, in our lethal C57BL/6J mouse model of H1N1pdm infection, global gene expression analysis indicated a pronounced IL-6 associated inflammatory response. Subsequently, we examined disease and outcome in IL-6 deficient mice infected with H1N1pdm. No significant differences in survival, weight loss, viral load, or pathology were observed between IL-6 deficient and wild-type mice following infection. Taken together, our findings suggest IL-6 may be a potential disease severity biomarker, but may not be a suitable therapeutic target in cases of severe H1N1pdm infection due to our mouse data.

A comprehensive analysis of reassortment in influenza A virus

SummaryGenetic reassortment plays a vital role in the evolution of the influenza virus and has historically been linked with the emergence of pandemic strains. Reassortment is believed to occur when a single host - typically swine - is simultaneously infected with multiple influenza strains. The reassorted viral strains with novel gene combinations tend to easily evade the immune system in other host species, satisfying the basic requirements of a virus with pandemic potential. Therefore, it is vital to continuously monitor the genetic content of circulating influenza strains and keep an eye out for new reassortants. We present a new approach to identify reassortants from large data sets of influenza whole genome nucleotide sequences and report the results of the first ever comprehensive search for reassortants of all published influenza A genomic data. 35 of the 52 well supported candidate reassortants we found are reported here for the first time while our analysis method offers new insight that enables us to draw a more detailed picture of the origin of some of the previously reported reassortants. A disproportionately high number (13/52) of the candidate reassortants found were the result of the introduction of novel hemagglutinin and/or neuraminidase genes into a previously circulating virus. The method described in this paper may contribute towards automating the task of routinely searching for reassortants among newly sequenced strains.

Differing clinical characteristics between influenza strains among young healthy adults in the tropics

BackgroundInfluenza infections may result in different clinical presentations. This study aims to determine the clinical differences between circulating influenza strains in a young healthy adult population in the tropics.MethodsA febrile respiratory illness (FRI) (fever ≥ 37.5°C with cough and/or sore throat) surveillance program was started in 4 large military camps in Singapore on May 2009. Personnel with FRI who visited the camp clinics from 11 May 2009 to 25 June 2010 were recruited. Nasal washes and interviewer-administered questionnaires on demographic information and clinical features were obtained from consenting participants. All personnel who tested positive for influenza were included in the study. Overall symptom load was quantified by counting the symptoms or signs, and differences between strains evaluated using linear models.ResultsThere were 434 (52.9%) pandemic H1N1-2009, 58 (7.1%) seasonal H3N2, 269 (32.8%) influenza B, and 10 (1.2%) seasonal H1N1 cases. Few seasonal influenza A (H1N1) infections were detected and were therefore excluded from analyses, together with undetermined influenza subtypes (44 (1.5%)), or more than 1 co-infecting subtype (6 (0.2%)). Pandemic H1N1-2009 cases had significantly fewer symptoms or signs (mean 7.2, 95%CI 6.9-7.4, difference 1.6, 95%CI 1.2-2.0, p < 0.001) than the other two subtypes (mean 8.7, 95%CI 8.5-9.0). There were no statistical differences between H3N2 and influenza B (p = 0.58). Those with nasal congestion, rash, eye symptoms, injected pharynx or fever were more likely to have H3N2; and those with sore throat, fever, injected pharynx or rhinorrhoea were more likely to have influenza B than H1N1-2009.ConclusionsInfluenza cases have different clinical presentations in the young adult population. Pandemic H1N1 influenza cases had fewer and milder clinical symptoms than seasonal influenza. As we only included febrile cases and had no information on the proportion of afebrile infections, further research is needed to confirm whether the relatively milder presentation of pandemic versus seasonal influenza infections applies to all infections or only febrile illnesses.

Comparative Analyses of Pandemic H1N1 and Seasonal H1N1, H3N2, and Influenza B Infections Depict Distinct Clinical Pictures in Ferrets

Influenza A and B infections are a worldwide health concern to both humans and animals. High genetic evolution rates of the influenza virus allow the constant emergence of new strains and cause illness variation. Since human influenza infections are often complicated by secondary factors such as age and underlying medical conditions, strain or subtype specific clinical features are difficult to assess. Here we infected ferrets with 13 currently circulating influenza strains (including strains of pandemic 2009 H1N1 [H1N1pdm] and seasonal A/H1N1, A/H3N2, and B viruses). The clinical parameters were measured daily for 14 days in stable environmental conditions to compare clinical characteristics. We found that H1N1pdm strains had a more severe physiological impact than all season strains where pandemic A/California/07/2009 was the most clinically pathogenic pandemic strain. The most serious illness among seasonal A/H1N1 and A/H3N2 groups was caused by A/Solomon Islands/03/2006 and A/Perth/16/2009, respectively. Among the 13 studied strains, B/Hubei-Wujiagang/158/2009 presented the mildest clinical symptoms. We have also discovered that disease severity (by clinical illness and histopathology) correlated with influenza specific antibody response but not viral replication in the upper respiratory tract. H1N1pdm induced the highest and most rapid antibody response followed by seasonal A/H3N2, seasonal A/H1N1 and seasonal influenza B (with B/Hubei-Wujiagang/158/2009 inducing the weakest response). Our study is the first to compare the clinical features of multiple circulating influenza strains in ferrets. These findings will help to characterize the clinical pictures of specific influenza strains as well as give insights into the development and administration of appropriate influenza therapeutics.

Update in Pulmonary Infections 2010

It is difficult to discuss the year in review for pulmonary infections without starting with the 2009 novel H1N1 influenza pandemic. Although excess deaths were reported for pediatric (1) and pregnant patients (2) from the prior year, the most surprising thing about the year 2010 is actually the lack of clinical infection with influenza. This resulted from a combination of factors. The first is that the novel 2009 H1N1 strain was the only circulating influenza strain during the 2009 to 2010 influenza season. The second is the dramatic effect of large-scale immunization against this particular strain. As can be seen in Figure 1, shortly after the vaccine became available, the rate of positive cultures reported to the CDC dropped dramatically (3). A similar pattern was seen with pediatric deaths, another CDC marker of influenza severity. The combination of vaccination and prior exposure during the spring of 2009 resulted in sufficient herd immunity to almost completely block new cases of influenza. Despite the ominous start, the 2009 to 2010 influenza season was actually associated with fewer deaths than in nonpandemic years. One of the lasting effects of this pandemic is a change in the standards of the Advisory Committee on Immunization Practices regarding eligibility for influenza vaccination; the committee now recommends seasonal influenza vaccination or all persons 6 months of age or older (4). The lung pathology of fatal cases of the novel H1N1 infections was reviewed by Mauad and colleagues (5). They describe three distinct pathologic findings: diffuse alveolar damage, necrotizing tracheobronchitis, and diffuse alveolar damage with diffuse alveolar hemorrhage. A subsequent letter suggests that most of the patients who had purulent tracheobronchitis also had concomitant bacterial pneumonia (6). This association supports the concept that viral damage to the airway mucosa may be important in the pathogenesis of secondary pneumonia. Documented bacterial pneumonia at onset of the H1N1 infection is uncommon, but ventilatorassociated pneumonia (VAP) often occurs as a consequence of the severe acute lung injury and prolonged mechanical ventilation (7). Therefore, the purulent tracheobronchitis may be part of the spectrum of VAP previously described in other autopsy series (8). COMMUNITY-ACQUIRED PNEUMONIA

Serologic assays for influenza surveillance, diagnosis and vaccine evaluation

Serological techniques play a critical role in various aspects of influenza surveillance, vaccine development and evaluation, and sometimes in diagnosis, particularly for novel influenza virus infections of humans. Because individuals are repeatedly exposed to antigenically and genetically diverse influenza viruses over a lifetime, the gold standard for detection of a recent influenza virus infection or response to current vaccination is the demonstration of a seroconversion, a fourfold or greater rise in antibody titer relative to a baseline sample, to a circulating influenza strain or vaccine component. The hemagglutination-inhibition assay remains the most widely used assay to detect strain-specific serum antibodies to influenza. The hemagglutination-inhibition assay is also used to monitor antigenic changes among influenza viruses which are constantly evolving; such antigenic data is essential for consideration of changes in influenza vaccine composition. The use of the hemagglutinin-specific microneutralization assay has increased, in part, owing to its sensitivity for detection of human antibodies to novel influenza viruses of animal origin. Neutralization assays using replication-incompetent pseudotyped particles may be advantageous in some laboratory settings for detection of antibodies to influenza viruses with heightened biocontainment requirements. The use of standardized protocols and antibody standards are important steps to improve reproducibility and interlaboratory comparability of results of serologic assays for influenza viruses.

Evaluation of Influenza-Specific Humoral Response by Microbead Array Analysis

Quantitation and determination of antigen specificity of systemic and mucosal immune responses to influenza vaccination is beneficial for future vaccine development. Previous methods to acquire this information were costly, time consuming and sample exhaustive. The benefits of suspension microbead array (MBA) analysis are numerous. The multiplex capabilities of the system conserve time, money and sample, while generating statistically powerful data. To demonstrate the use of the assay by comparing the humoral influenza-specific responses of two cohorts from two countries that differed in circulating influenza strains and rates of influenza vaccination. Influenza hemagglutinin (HA) from different strains were coated on microbeads and incubated with serum samples to capture immunoglobulin (Ig) A(1) and IgG(1) host antibodies. Statistically significant differences in IgA(1) and IgG(1) exist between the serum samples from Winnipeg (Manitoba) donors and those from Kenyan (Africa) donors. Data were compared using Mann-Whitney nonparametric tests. The Winnipeg donors had higher mean fluorescence intensity values, with significant P values for anti-HA IgA(1) to A/Wyoming/3/2003 (P=0.044), A/Vietnam/1203/2004 (P=0.0179), A/New Caledonia/20/99 (P<0.0001) and B/Tokyo/53/99 (P=0.0002). No differences were seen between the groups in their response to B/Jilin/20/2003. The Winnipeg donors had higher mean fluorescence intensity values, with significant P values for anti-HA IgG(1) to A/Wyoming/3/2003 (P=0.0135), B/Tokyo/53/99 (P=0.006) and B/Jilin20/2003 (P=0.026). Influenza-specific IgA(1) and IgG(1) antibodies were successfully detected using MBA technology. A significant difference in antibody response was observed between Winnipeg and Kenyan donor serums. MBA analysis is a relatively quick and cost-effective method for serum antibody analysis. The potential to simultaneously assay small sample volumes for a multitude of antigens makes this method invaluable for future vaccine response monitoring.