Results from the WHO external quality assessment for the respiratory syncytial virus pilot, 2016-17.

BACKGROUND: External quality assessments (EQAs) for the molecular detection of respiratory syncytial virus (RSV) are necessary to ensure the provision of reliable and accurate results. One of the objectives of the pilot of the World Health Organization (WHO) Global RSV Surveillance, 2016-2017, was to evaluate and standardize RSV molecular tests used by participating countries. This paper describes the first WHO RSV EQA for the molecular detection of RSV. METHODS: The WHO implemented the pilot of Global RSV Surveillance based on the WHO Global Influenza Surveillance and Response System (GISRS) from 2016 to 2018 in 14 countries. To ensure standardization of tests, 13 participating laboratories were required to complete a 12 panel RSV EQA prepared and distributed by the Centers for Disease Control and Prevention (CDC), USA. The 14th laboratory joined the pilot late and participated in a separate EQA. Laboratories evaluated a RSV rRT-PCR assay developed by CDC and compared where applicable, other Laboratory Developed Tests (LDTs) or commercial assays already in use at their laboratories. RESULTS: Laboratories performed well using the CDC RSV rRT-PCR in comparison with LDTs and commercial assays. Using the CDC assay, 11 of 13 laboratories reported correct results. Two laboratories each reported one false-positive finding. Of the laboratories using LDTs or commercial assays, results as assessed by Ct values were 100% correct for 1/5 (20%). With corrective actions, all laboratories achieved satisfactory outputs. CONCLUSIONS: These findings indicate that reliable results can be expected from this pilot. Continued participation in EQAs for the molecular detection of RSV is recommended.

Pandemic influenza A(H1N1pdm09) vaccine induced high levels of influenza-specific IgG and IgM antibodies as analyzed by enzyme immunoassay and dual-mode multiplex microarray immunoassay methods.

Influenza A viruses continue to circulate throughout the world as yearly epidemics or occasional pandemics. Influenza infections can be prevented by seasonal multivalent or monovalent pandemic vaccines. In the present study, we describe a novel multiplex microarray immunoassay (MAIA) for simultaneous measurement of virus-specific IgG and IgM antibodies using Pandemrix-vaccinated adult sera collected at day 0 and 28 and 180 days after vaccination as the study material. MAIA showed excellent correlation with a conventional enzyme immunoassay (EIA) in both IgG and IgM anti-influenza A antibodies and good correlation with hemagglutination inhibition (HI) test. Pandemrix vaccine induced 5-30 fold increases in anti-H1N1pdm09 influenza antibodies as measured by HI, EIA or MAIA. A clear increase in virus-specific IgG antibodies was found in 93-97% of vaccinees by MAIA and EIA. Virus-specific IgM antibodies were found in 90-92% of vaccinees by MAIA and EIA, respectively and IgM antibodies persisted for up to 6 months after vaccination in 55-62% of the vaccinees. Pandemic influenza vaccine induced strong anti-influenza A IgG and IgM responses that persisted several months after vaccination. MAIA was demonstrated to be an excellent method for simultaneous measurement of antiviral IgG and IgM antibodies against multiple virus antigens. Thus the method is well suitable for large scale epidemiological and vaccine immunity studies.

Leveraging the Global Influenza Surveillance and Response System for global respiratory syncytial virus surveillance-opportunities and challenges.

BACKGROUND: Respiratory syncytial virus (RSV)-associated acute lower respiratory infection is a common cause for hospitalization and hospital deaths in young children globally. There is urgent need to generate evidence to inform immunization policies when RSV vaccines become available. The WHO piloted a RSV surveillance strategy that leverages the existing capacities of the Global Influenza Surveillance and Response System (GISRS) to better understand RSV seasonality, high-risk groups, validate case definitions, and develop laboratory and surveillance standards for RSV. METHODS: The RSV sentinel surveillance strategy was piloted in 14 countries. Patients across all age groups presenting to sentinel hospitals and clinics were screened all year-round using extended severe acute respiratory infection (SARI) and acute respiratory infection (ARI) case definitions for hospital and primary care settings, respectively. Respiratory specimens were tested for RSV at the National Influenza Centre (NIC) using standardized molecular diagnostics that had been validated by an External Quality Assurance program. The WHO FluMart data platform was adapted to receive case-based RSV data and visualize interactive visualization outputs. RESULTS: Laboratory standards for detecting RSV by RT-PCR were developed. A review assessed the feasibility and the low incremental costs for RSV surveillance. Several challenges were addressed related to case definitions, sampling strategies, the need to focus surveillance on young children, and the data required for burden estimation. CONCLUSIONS: There was no evidence of any significant adverse impact on the functioning of GISRS which is primarily intended for virologic and epidemiological surveillance of influenza.

65 years of influenza surveillance by a World Health Organization-coordinated global network.

The 1918 devastating influenza pandemic left a lasting impact on influenza experts and the public, and the importance of global influenza surveillance was soon recognized. The World Health Organization (WHO) Global Influenza Surveillance Network (GISN) was founded in 1952 and renamed to Global Influenza Surveillance and Response System in 2011 upon the adoption by the World Health Assembly, of the Pandemic Influenza Preparedness Framework for the Sharing of Influenza Viruses and Access to Vaccines and Other Benefits ("PIP Framework"). The importance of influenza surveillance had been recognized and promoted by experts prior to the years leading up to the establishment of WHO. In the 65 years of its existence, the Network has grown to comprise 143 National Influenza Centers recognized by WHO, 6 WHO Collaborating Centers, 4 Essential Regulatory Laboratories, and 13 H5 Reference Laboratories. The Network has proven its excellence throughout these 65 years, providing detailed information on circulating seasonal influenza viruses, as well as immediate response to the influenza pandemics in 1957, 1968, and 2009, and to threats caused by animal influenza viruses and by zoonotic transmission of coronaviruses. For its central role in global public health, the Network has been highly recognized by its many partners and by international bodies. Several generations of world-renowned influenza scientists have brought the Network to where it is now and they will take it forward to the future, as influenza will remain a preeminent threat to humans and to animals.

Improving the selection and development of influenza vaccine viruses - Report of a WHO informal consultation on improving influenza vaccine virus selection, Hong Kong SAR, China, 18-20 November 2015.

Since 2010 the WHO has held a series of informal consultations to explore ways of improving the currently highly complex and time-pressured influenza vaccine virus selection and development process. In November 2015 experts from around the world met to review the current status of efforts in this field. Discussion topics included strengthening influenza surveillance activities to increase the availability of candidate vaccine viruses and improve the extent, timeliness and quality of surveillance data. Consideration was also given to the development and potential application of newer laboratory assays to better characterize candidate vaccine viruses, the potential importance of antibodies directed against influenza virus neuraminidase, and the role of vaccine effectiveness studies. Advances in next generation sequencing and whole genome sequencing of influenza viruses were also discussed, along with associated developments in synthetic genomics technologies, evolutionary analysis and predictive mathematical modelling. Discussions were also held on the late emergence of an antigenic variant influenza A(H3N2) virus in mid-2014 that could not be incorporated in time into the 2014-15 northern hemisphere vaccine. There was broad recognition that given the current highly constrained influenza vaccine development and production timeline it would remain impossible to incorporate any variant virus which emerged significantly long after the relevant WHO biannual influenza vaccine composition meetings. Discussions were also held on the development of pandemic and broadly protective vaccines, and on associated regulatory and manufacturing requirements and constraints. With increasing awareness of the health and economic burdens caused by seasonal influenza, the ever-present threat posed by zoonotic influenza viruses, and the significant impact of the 2014-15 northern hemisphere seasonal influenza vaccine mismatch, this consultation provided a very timely opportunity to share developments and exchange views. In all areas, a renewed and strengthened emphasis was placed on developing concrete and measurable actions and identifying the key stakeholders responsible for their implementation.

Molecular characterization of adenoviruses among finnish military conscripts.

Although adenoviruses were identified as important respiratory pathogens many years ago, little information is available concerning the prevalence of different adenovirus serotypes, which are circulating and causing epidemics in Finnish military training centers. Over a period of five years from 2008 to 2012, 3577 respiratory specimens were collected from military conscripts presenting with symptoms compatible with acute respiratory tract infection. Upon initial testing for certain respiratory viruses by real-time PCR, 837 of these specimens were identified as adenovirus-positive. For 672 of these specimens, the serotype of the adenovirus responsible was successfully determined by DNA sequencing. Serotypes 1, 2, 3, and 4 were detected in 1, 3, 181, and 487 samples, respectively. Adenovirus epidemics were observed during each year of this study. Based on these findings, adenovirus vaccination should be considered for military conscripts in the Finnish Defence Forces.

Strengthening the influenza vaccine virus selection and development process: Report of the 3rd WHO Informal Consultation for Improving Influenza Vaccine Virus Selection held at WHO headquarters, Geneva, Switzerland, 1-3 April 2014.

Despite long-recognized challenges and constraints associated with their updating and manufacture, influenza vaccines remain at the heart of public health preparedness and response efforts against both seasonal and potentially pandemic influenza viruses. Globally coordinated virological and epidemiological surveillance is the foundation of the influenza vaccine virus selection and development process. Although national influenza surveillance and reporting capabilities are being strengthened and expanded, sustaining and building upon recent gains has become a major challenge. Strengthening the vaccine virus selection process additionally requires the continuation of initiatives to improve the timeliness and representativeness of influenza viruses shared by countries for detailed analysis by the WHO Global Influenza Surveillance and Response System (GISRS). Efforts are also continuing at the national, regional, and global levels to better understand the dynamics of influenza transmission in both temperate and tropical regions. Improved understanding of the degree of influenza seasonality in tropical countries of the world should allow for the strengthening of national vaccination policies and use of the most appropriate available vaccines. There remain a number of limitations and difficulties associated with the use of HAI assays for the antigenic characterization and selection of influenza vaccine viruses by WHOCCs. Current approaches to improving the situation include the more-optimal use of HAI and other assays; improved understanding of the data produced by neutralization assays; and increased standardization of serological testing methods. A number of new technologies and associated tools have the potential to revolutionize influenza surveillance and response activities. These include the increasingly routine use of whole genome next-generation sequencing and other high-throughput approaches. Such approaches could not only become key elements in outbreak investigations but could drive a new surveillance paradigm. However, despite the advances made, significant challenges will need to be addressed before next-generation technologies become routine, particularly in low-resource settings. Emerging approaches and techniques such as synthetic genomics, systems genetics, systems biology and mathematical modelling are capable of generating potentially huge volumes of highly complex and diverse datasets. Harnessing the currently theoretical benefits of such bioinformatics ("big data") concepts for the influenza vaccine virus selection and development process will depend upon further advances in data generation, integration, analysis and dissemination. Over the last decade, growing awareness of influenza as an important global public health issue has been coupled to ever-increasing demands from the global community for more-equitable access to effective and affordable influenza vaccines. The current influenza vaccine landscape continues to be dominated by egg-based inactivated and live attenuated vaccines, with a small number of cell-based and recombinant vaccines. Successfully completing each step in the annual influenza vaccine manufacturing cycle will continue to rely upon timely and regular communication between the WHO GISRS, manufacturers and regulatory authorities. While the pipeline of influenza vaccines appears to be moving towards a variety of niche products in the near term, it is apparent that the ultimate aim remains the development of effective "universal" influenza vaccines that offer longer-lasting immunity against a broad range of influenza A subtypes.

Efficient replication and strong induction of innate immune responses by H9N2 avian influenza virus in human dendritic cells.

Avian influenza A (H9N2) viruses have occasionally been identified in humans with upper respiratory tract infections. The novel H7N9/2013 virus identified in China shows that a low pathogenic avian influenza (LPAI) virus can be highly pathogenic in humans. Therefore, it is important to understand virus-host cell interactions and immune responses triggered by LPAI viruses in humans. We found that LPAI A/Hong Kong/1073/99 (H9N2) virus replicated efficiently in human dendritic cells (DCs). The H9N2 virus induced strong IFN gene expression although with different kinetics than seasonal influenza A/Beijing/353/89 (H3N2) virus. IFN inducible antiviral proteins were produced in H9N2 virus-infected cells at the same level as in H3N2 infection. The H9N2 virus was extremely sensitive to the antiviral actions of type I IFNs. These results indicate that the avian influenza H9N2 virus is inducing a strong antiviral IFN response in human DCs.

Effectiveness of pandemic and seasonal influenza vaccines in preventing laboratory-confirmed influenza in adults: a clinical cohort study during epidemic seasons 2009-2010 and 2010-2011 in Finland.

BACKGROUND: One dose of pandemic influenza vaccine Pandemrix (GlaxoSmithKline) was offered to the entire population of Finland in 2009-10. We conducted a prospective clinical cohort study to determine the vaccine effectiveness in preventing febrile laboratory-confirmed influenza infection during the influenza season 2009-10 and continued the study in 2010-11. METHODS: In total, 3,518 community dwelling adults aged 18-75 years living in Tampere city were enrolled. The participants were not assigned to any vaccination regimen, but they could participate in the study regardless of their vaccination status or intention to be vaccinated with the pandemic or seasonal influenza vaccine. They were asked to report if they received Pandemrix in 2009-10 and/or trivalent influenza vaccine in 2010-11. Vaccinations were verified from medical records. The participants were instructed to report all acute symptoms of respiratory tract infection with fever (at least 38°C) and pneumonias to the study staff. Nasal and oral swabs were obtained within 5-7 days after symptom onset and influenza-specific RNA was identified by reverse transcription polymerase chain reaction. RESULTS: In 2009-10, the estimated vaccine effectiveness was 81% (95%CI 30-97). However, the vaccine effectiveness could not be estimated reliably, because only persons in prioritized groups were vaccinated before/during the first pandemic wave and many participants were enrolled when they already had the symptoms of A(H1N1)pdm09 influenza infection. In 2010-11, 2,276 participants continued the follow-up. The vaccine effectiveness, adjusted for potential confounding factors was 81% (95%CI 41-96) for Pandemrix only and 88% (95%CI 63-97) for either Pandemrix or trivalent influenza vaccine 2010-11 or both, respectively. CONCLUSION: Vaccination with an AS03-adjuvanted pandemic vaccine in 2009-10 was still effective in preventing A(H1N1)pdm09 influenza during the following epidemic season in 2010-11. TRIAL REGISTRATION: ClinicalTrials.gov NCT01024725. NCT01206114.

Impact of influenza B lineage-level mismatch between trivalent seasonal influenza vaccines and circulating viruses, 1999-2012.

BACKGROUND: Influenza B virus strains in trivalent influenza vaccines are frequently mismatched to the circulating B strains, but the population-level impact of such mismatches is unknown. We assessed the impact of vaccine mismatch on the epidemiology of influenza B during 12 recent seasonal outbreaks of influenza in Finland. METHODS: We analyzed all available nationwide data on virologically confirmed influenza infections in all age groups in Finland between 1 July 1999 and 30 June 2012, with the exclusion of the pandemic season of 2009-2010. We derived data on influenza infections and the circulation of different lineages of B viruses during each season from the Infectious Diseases Register and the National Influenza Center, National Institute for Health and Welfare, Finland. RESULTS: A total of 34 788 cases of influenza were recorded. Influenza A accounted for 74.0% and influenza B for 26.0% of all typed viruses. Throughout the 12 seasons, we estimated that 41.7% (3750 of 8993) of all influenza B infections were caused by viruses representing the other genetic lineage than the one in the vaccine. Altogether, opposite-lineage influenza B viruses accounted for 10.8% of all influenza infections in the population, the proportion being highest (16.8%) in children aged 10-14 years and lowest (2.6%) in persons aged ≥70 years. CONCLUSIONS: The population-level impact of lineage-level mismatch between the vaccine and circulating strains of influenza B viruses is substantial, especially among children and adolescents. The results provide strong support for the inclusion of both influenza B lineages in seasonal influenza vaccines.

Performance characteristics of qualified cell lines for isolation and propagation of influenza viruses for vaccine manufacturing.

Cell culture is now available as a method for the production of influenza vaccines in addition to eggs. In accordance with currently accepted practice, viruses recommended as candidates for vaccine manufacture are isolated and propagated exclusively in hens' eggs prior to distribution to manufacturers. Candidate vaccine viruses isolated in cell culture are not available to support vaccine manufacturing in mammalian cell bioreactors so egg-derived viruses have to be used. Recently influenza A (H3N2) viruses have been difficult to isolate directly in eggs. As mitigation against this difficulty, and the possibility of no suitable egg-isolated candidate viruses being available, it is proposed to consider using mammalian cell lines for primary isolation of influenza viruses as candidates for vaccine production in egg and cell platforms. To investigate this possibility, we tested the antigenic stability of viruses isolated and propagated in cell lines qualified for influenza vaccine manufacture and subsequently investigated antigen yields of such viruses in these cell lines at pilot-scale. Twenty influenza A and B-positive, original clinical specimens were inoculated in three MDCK cell lines. The antigenicity of recovered viruses was tested by hemagglutination inhibition using ferret sera against contemporary vaccine viruses and the amino acid sequences of the hemagglutinin and neuraminidase were determined. MDCK cell lines proved to be highly sensitive for virus isolation. Compared to the virus sequenced from the original specimen, viruses passaged three times in the MDCK lines showed up to 2 amino acid changes in the hemagglutinin. Antigenic stability was also established by hemagglutination inhibition titers comparable to those of the corresponding reference virus. Viruses isolated in any of the three MDCK lines grew reasonably well but variably in three MDCK cells and in VERO cells at pilot-scale. These results indicate that influenza viruses isolated in vaccine certified cell lines may well qualify for use in vaccine production.

Decline in temperature and humidity increases the occurrence of influenza in cold climate.

BACKGROUND: Both temperature and humidity may independently or jointly contribute to the risk of influenza infections. We examined the relations between the level and decrease of temperature, humidity and the risk of influenza A and B virus infections in a subarctic climate. METHODS: We conducted a case-crossover study among military conscripts (n = 892) seeking medical attention due to respiratory symptoms during their military training period and identified 66 influenza A and B cases by PCR or serology. Meteorological data such as measures of average and decline in ambient temperature and absolute humidity (AH) during the three preceding days of the onset (hazard period) and two reference periods, prior and after the onset were obtained. RESULTS: The average temperature preceding the influenza onset was -6.8 ± 5.6°C and AH 3.1 ± 1.3 g/m3. A decrease in both temperature and AH during the hazard period increased the occurrence of influenza so that a 1°C decrease in temperature and 0.5 g decrease per m3 in AH increased the estimated risk by 11% [OR 1.11 (1.03 to 1.20)] and 58% [OR 1.58 (1.28 to 1.96)], respectively. The occurrence of influenza infections was positively associated with both the average temperature [OR 1.10 per 1°C (95% confidence interval 1.02 to 1.19)] and AH [OR 1.25 per g/m3 (1.05 to 1.49)] during the hazard period prior to onset. CONCLUSION: Our results demonstrate that a decrease rather than low temperature and humidity per se during the preceding three days increase the risk of influenza episodes in a cold climate.

Incidence and etiology of community-acquired pneumonia in the elderly in a prospective population-based study.

BACKGROUND: We conducted a prospective population-based epidemiological study to prepare a setting for documentation of the efficacy of novel vaccines against pneumococcal (Pnc) community-acquired pneumonia (CAP) in the elderly. Specific objectives were to demonstrate setting feasibility, to construct a case definition for Pnc CAP, and to estimate its incidence. METHODS: We prospectively enrolled patients with clinical and radiological findings compatible with CAP at municipal on-call clinics serving an elderly population (age ≥ 65 y) of approximately 29,500. Sputum, urine, nasopharyngeal swab (NPS), and blood samples were analyzed using diverse methods for the identification of Pnc (culture, PCR, antigen tests, serology) and of other pathogens. The following case definition for Pnc CAP was derived: encapsulated Pnc in blood culture or in high-quality sputum culture or at least 2 of the following: positive urine Pnc antigen; ≥ 2-fold increase in serum anti-PsaA or anti-CbpA antibodies; encapsulated Pnc culture or LytA PCR in either sputum or NPS. RESULTS: We enrolled 490 clinical CAP patients during the 2-y follow-up, 53% of all clinical CAP patients in the source population; 323 were radiologically confirmed. The incidence of radiologically confirmed CAP was 5.5/1000 person-y (95% confidence interval (CI) 4.9-6.1) and 10.5/1000 person-y when adjusted for non-captured patients. The proportion of radiologically confirmed CAP caused by Pnc was estimated at 17%; i.e. 0.95/1000 person-y (95% CI 0.7-1.2) and 1.8 when adjusted for non-captured patients. CONCLUSIONS: We developed and documented a feasible methodology for capturing endpoints in a vaccine trial for the prevention of pneumonia. CAP incidence in the elderly population remains considerable and Streptococcus pneumoniae was one of the most commonly detected causative agents.

Influenza C virus infection in military recruits--symptoms and clinical manifestation.

Due to the lack of rapid diagnostic tests, clinical features of Influenza C virus infections are poorly characterized. Respiratory infections in military recruits in eastern Finland were monitored between July 2004 and December 2005 in order to study the epidemiology and clinical picture of infections caused by this virus. Blood samples were obtained at entry and at the end of the military service, and during each episode of respiratory infection to measure antibody responses against 10 viral and 2 bacterial pathogens. If possible, sputum samples were collected during the acute phase of respiratory infection episodes. Symptoms of the episodes were recorded for comparison of the clinical picture caused by various infectious agents. Infection with influenza C virus was detected in 38 of 892 young men during their service. The virus usually caused a mild upper respiratory tract infection. Most typical clinical features of influenza C virus infection were cough, rhinitis, and hoarseness. A striking difference to infections caused by influenza A virus was the lack of fever. Influenza C virus is an important cause of a respiratory tract infection in army conscripts. Infections with this virus are usually mild but can be complicated in some cases.

The use of the probiotic Lactobacillus rhamnosus GG and viral findings in the nasopharynx of children attending day care.

Limited data are available on the effects of probiotics on the nasopharyngeal presence of respiratory viruses in children attending day care. In this substudy of a randomized, double-blinded, placebo-controlled 28-week intervention study, nasopharyngeal swab samples were collected, on visits to a physician due to symptoms of infection, from children receiving control milk (N = 97) and children receiving the same milk supplemented with probiotic Lactobacillus rhamnosus GG (N = 97). The presence of 14 respiratory viruses was assessed by PCR methods, and viral findings were compared with symptom prevalences in the intervention groups. Rhinovirus was identified in 28.6% of 315 swab samples, followed by respiratory syncytial virus (12.4%), parainfluenza virus 1 (12.1%), enterovirus (8.9%), influenza A(H1N1)pdm09 (7.9%), human bocavirus 1 (3.8%), parainfluenza virus 2 (3.2%), adenovirus (2.9%), and influenza A(H3N2) (0.6%). The children in the probiotic group had less days with respiratory symptoms per month than the children in the control group (6.48 [95% CI 6.28-6.68] vs. 7.19 [95% CI 6.98-7.41], P < 0.001). Probiotic intervention did not reduce significantly the occurrence of the examined respiratory viruses, or have an effect on the number of respiratory symptoms observed at the time of a viral finding. Rhinovirus, respiratory syncytial virus, and parainfluenza virus 1 were the most common respiratory viruses in symptomatic children. Children receiving Lactobacillus rhamnosus GG had fewer days with respiratory symptoms than children in the control group, although probiotic intervention was not effective in reducing the amount of viral findings or the respiratory symptoms associated with viral findings.

Antibody responses against influenza A(H1N1)pdm09 virus after sequential vaccination with pandemic and seasonal influenza vaccines in Finnish healthcare professionals.

BACKGROUND: Influenza A(H1N1)pdm09 virus has been circulating in human population for three epidemic seasons. During this time, monovalent pandemic and trivalent seasonal influenza vaccination against this virus have been offered to Finnish healthcare professionals. It is, however, unclear how well vaccine-induced antibodies recognize different strains of influenza A(H1N1)pdm09 circulating in the population and whether the booster vaccination with seasonal influenza vaccine would broaden the antibody cross-reactivity. OBJECTIVES: Influenza vaccine-induced humoral immunity against several isolates of influenza A(H1N1)pdm09 virus was analyzed in healthcare professionals. Age-dependent responses were also analyzed. METHODS: Influenza viruses were selected to represent viruses that circulated in Finland during two consecutive influenza epidemic seasons 2009-2010 and 2010-2011. Serum samples from vaccinated volunteers, age 20-64 years, were collected before and after vaccination with AS03-adjuvanted pandemic and non-adjuvanted trivalent seasonal influenza vaccine that was given 1 year later. RESULTS: Single dose of pandemic vaccine induced a good albeit variable antibody response. On day 21 after vaccination, depending on the virus strain, 14-75% of vaccinated had reached antibody titers (≥1:40) considered seroprotective. The booster vaccination 1 year later with a seasonal vaccine elevated the seroprotection rate to 57-98%. After primary immunization, younger individuals (20-48 years) had significantly higher antibody titers against all tested viruses than older persons (49-64 years) but this difference disappeared after the seasonal booster vaccination. CONCLUSIONS: Even a few amino acid changes in influenza A HA may compromise the vaccine-induced antibody recognition. Older adults (49 years and older) may benefit more from repeated influenza vaccinations.

[Influenza viruses--a challenge for vaccinations]. / Influenssavirukset--haaste rokotuksille.

The clinical picture of influenza may vary from mild respiratory infection to pneumonia requiring intensive care. Annual epidemics are most commonly caused by H3N2 or H1N1 type influenza A or influenza B viruses. The population's immune protection against a new virus type is low, whereupon morbidity and mortality may be high. Vaccinations are the most important means to decrease influenza morbidity. Annual variation and quick intercontinental migration of influenza viruses, combined with the possibility of the creation of reassortant viruses, are significant challenges for the development of influenza vaccines.

Predominance of heterosubtypic IFN-γ-only-secreting effector memory T cells in pandemic H1N1 naive adults.

The 2009/10 pandemic (pH1N1) highlighted the need for vaccines conferring heterosubtypic immunity against antigenically shifted influenza strains. Although cross-reactive T cells are strong candidates for mediating heterosubtypic immunity, little is known about the population-level prevalence, frequency, and cytokine-secretion profile of heterosubtypic T cells to pH1N1. To assess this, pH1N1 sero-negative adults were recruited. Single-cell IFN-γ and IL-2 cytokine-secretion profiles to internal proteins of pH1N1 or live virus were enumerated and characterised. Heterosubtypic T cells recognising pH1N1 core proteins were widely prevalent, being detected in 90% (30 of 33) of pH1N1-naïve individuals. Although the last exposure to influenza was greater than 6 months ago, the frequency and proportion of the IFN-γ-only-secreting T-cell subset was significantly higher than the IL-2-only-secreting subset. CD8(+) IFN-γ-only-secreting heterosubtypic T cells were predominantly CCR7(-) CD45RA(-) effector-memory phenotype, expressing the tissue-homing receptor CXCR3 and degranulation marker CD107. Receipt of the 2008-09 influenza vaccine did not alter the frequency of these heterosubtypic T cells, highlighting the inability of current vaccines to maintain this heterosubtypic T-cell pool. The surprisingly high prevalence of pre-existing circulating pH1N1-specific CD8(+) IFN-γ-only-secreting effector memory T cells with cytotoxic and lung-homing potential in pH1N1-seronegative adults may partly explain the low case fatality rate despite high rates of infection of the pandemic in young adults.