Changes in the hemagglutinins and neuraminidases of human influenza B viruses isolated in Italy during the 2001-02, 2002-03, and 2003-04 seasons

Molecular characterization and evolution dynamics of influenza B viruses circulating in Germany from season 1996/1997 to 2019/2020

Influenza B viruses are responsible for significant disease burden caused by viruses of both the Yamagata- and Victoria-lineage. Since the circulating patterns of influenza B viruses in different countries vary we investigated molecular properties and evolution dynamics of influenza B viruses circulating in Germany between 1996 and 2020. A change of the dominant lineage occurred in Germany in seven seasons in over past 25 years. A total of 676 sequences of hemagglutinin coding domain 1 (HA1) and 516 sequences of neuraminidase (NA) genes of Yamagata- and Victoria-lineage viruses were analyzed using time-scaled phylogenetic tree. Phylogenetic analysis demonstrated that Yamagata-lineage viruses are more diverse than the Victoria-lineage viruses and could be divided into nine genetic groups whereas Victoria-lineage viruses presented six genetic groups. Comparative phylogenetic analyses of both the HA and NA segments together revealed a number of inter-lineage as well as inter- and intra-clade reassortants. We identified key amino acid substitutions in major HA epitopes such as in four antigenic sites and receptor-binding sites (RBS) and in the regions close to them, with most substitutions in the 120-loop of both lineage viruses. Altogether, seventeen substitutions were fixed over time within the Yamagata-lineage with twelve of them in the antigenic sites. Thirteen substitutions were identified within the Victoria-lineage, with eleven of them in the antigenic sites. Moreover, all Victoria-lineage viruses of the 2017/2018 season were characterized by a deletion of two amino acids at the position 162-163 in the antigenic site of HA1. The viruses with triple deletion Δ162-164 were found in Germany since season 2018/2019. We highlighted the interplay between substitutions in the glycosylation sites and RBS and antigenic epitope during HA evolution. The results obtained underscore the need for continuous monitoring of circulating influenza B viruses. Early detection of strains with genetic and antigenic variation is essential to predict the circulation patterns for the following season. Such information is important for the development of optimal vaccines and strategies for prevention and control of influenza.

Effectiveness of Trivalent and Quadrivalent Inactivated Vaccines Against Influenza B in the United States, 2011-2012 to 2016-2017

Background

Since 2013, quadrivalent influenza vaccines containing 2 B viruses gradually replaced trivalent vaccines in the United States. We compared the vaccine effectiveness of quadrivalent to trivalent inactivated vaccines (IIV4 to IIV3, respectively) against illness due to influenza B during the transition, when IIV4 use increased rapidly.

Methods

The US Influenza Vaccine Effectiveness (Flu VE) Network analyzed 25 019 of 42 600 outpatients aged ≥6 months who enrolled within 7 days of illness onset during 6 seasons from 2011–2012. Upper respiratory specimens were tested for the influenza virus type and B lineage. Using logistic regression, we estimated IIV4 or IIV3 effectiveness by comparing the odds of an influenza B infection overall and the odds of B lineage among vaccinated versus unvaccinated participants. Over 4 seasons from 2013–2014, we compared the relative odds of an influenza B infection among IIV4 versus IIV3 recipients.

Results

Trivalent vaccines included the predominantly circulating B lineage in 4 of 6 seasons. During 4 influenza seasons when both IIV4 and IIV3 were widely used, the overall effectiveness against any influenza B was 53% (95% confidence interval [CI], 45–59) for IIV4 versus 45% (95% CI, 34–54) for IIV3. IIV4 was more effective than IIV3 against the B lineage not included in IIV3, but comparative effectiveness against illnesses related to any influenza B favored neither vaccine valency.

Conclusions

The uptake of quadrivalent inactivated influenza vaccines was not associated with increased protection against any influenza B illness, despite the higher effectiveness of quadrivalent vaccines against the added B virus lineage. Public health impact and cost-benefit analyses are needed globally.

Trends of influenza B during the 2010-2016 seasons in 2 regions of north and south Italy: The impact of the vaccine mismatch on influenza immunisation strategy

Influenza A and B viruses are responsible for respiratory infections, representing globally seasonal threats to human health. The 2 viral types often co-circulate and influenza B plays an important role in the spread of infection. A 6-year retrospective surveillance study was conducted between 2010 and 2016 in 2 large administrative regions of Italy, located in the north (Liguria) and in the south (Sicily) of the country, to describe the burden and epidemiology of both B/Victoria and B/Yamagata lineages in different healthcare settings. Influenza B viruses were detected in 5 of 6 seasonal outbreaks, exceeding influenza A during the season 2012-2013. Most of influenza B infections were found in children aged ≤ 14 y and significant differences were observed in the age-groups infected by the different lineages. B/Victoria strains prevailed in younger population than B/Yamagata, but also were more frequently found in the community setting. Conversely, B/Yamagata viruses were prevalent among hospitalized cases suggesting their potential role in the development of more severe disease. The relative proportions of viral lineages varied from year to year, resulting in different lineage-level mismatch for the B component of trivalent influenza vaccine. Our findings confirmed the need for continuous virological surveillance of seasonal epidemics and bring attention to the adoption of universal influenza immunization program in the childhood. The use of tetravalent vaccine formulations may be useful to improve the prevention and control of the influenza burden in general population.

Fifteen years of epidemiologic, virologic and syndromic influenza surveillance: A focus on type B virus and the effects of vaccine mismatch in Liguria region, Italy

In order to estimate the burden of influenza and to describe the genetic evolutionary pattern and antigenic variability of type B viral strains, data deriving from 3 surveillance systems active in Liguria region, Northern Italy, were described. Since the re-emergence of the Victoria lineage in 2001, the clinical-epidemiological and syndromic surveillances demonstrated the heavy burden of influenza like illness (ILI) syndrome. Focusing on type B influenza virus, it predominated or played a relevant epidemic role in the 50% of the evaluated influenza seasons. Furthermore, the virologic surveillance demonstrated the frequent co-circulation of both lineages an heterogeneous circulation of different influenza B strains, determining a partial or complete mismatch in at least 6 influenza seasons. The undemonstrated cross-reactivity between lineages and the unpredictability of predominant lineage arose the scientific debate about the opportunity to include the quadrivalent influenza vaccine among the preventive tools to improve the protection against type B viruses. The integration of different surveillance systems highly contribute to estimate the poorly evaluated burden of type B influenza virus and help to find variants to include in the vaccine formulation.

Immunogenicity and safety of inactivated quadrivalent influenza vaccine in adults: A systematic review and meta-analysis of randomised controlled trials

BACKGROUND

A quadrivalent influenza vaccine (QIV) includes two A strains (A/H1N1, A/H3N2) and two B lineages (B/Victoria, B/Yamagata). The presence of both B lineages eliminate potential B lineage mismatch of trivalent influenza vaccine (TIV) with the circulating strain.

METHODS

Electronic database searches of Medline, Embase, Cochrane Central Register of Controlled Trials (CCRCT), Scopus and Web of Science were conducted for articles published until June 30, 2015 inclusive. Articles were limited to randomised controlled trials (RCTs) in adults using inactivated intramuscular vaccine and published in English language only. Summary estimates of immunogenicity (by seroprotection and seroconversion rates) and adverse events outcomes were compared between QIV and TIV, using a risk ratio (RR). Studies were pooled using inverse variance weights with a random effect model and the I(2) statistic was used to estimate heterogeneity.

RESULTS

A total of five RCTs were included in the meta-analysis. For immunogenicity outcomes, QIV had similar efficacy for the three common strains; A/H1N1, A/H3N2 and the B lineage included in the TIV. QIV also showed superior efficacy for the B lineage not included in the TIV; pooled seroprotection RR of 1.14 (95%CI: 1.03-1.25, p=0.008) and seroconversion RR of 1.78 (95%CI: 1.24-2.55, p=0.002) for B/Victoria, and pooled seroprotection RR of 1.12 (95%CI: 1.02-1.22, p=0.01) and seroconversion RR of 2.11 (95%CI: 1.51-2.95, p<0.001) for B/Yamagata, respectively. No significant differences were found between QIV and TIV for aggregated local and systemic adverse events within 7days post-vaccination. There were no vaccine-related serious adverse events reported for either QIV or TIV. Compared to TIV, injection-site pain was more common for QIV, with a pooled RR of 1.18 (95%CI: 1.03-1.35, p=0.02).

CONCLUSION

In adults, inactivated QIV was as immunogenic as seasonal TIV, with equivalent efficacy against the shared three strains included in TIV, and a superior immunogenicity against the non-TIV B lineage.

The Molecular Epidemiology and Evolutionary Dynamics of Influenza B Virus in Two Italian Regions during 2010-2015: The Experience of Sicily and Liguria

Molecular epidemiology of influenza B virus remained poorly studied in Italy, despite representing a major contributor to seasonal epidemics. This study aimed to reconstruct the phylogenetic relationships and genetic diversity of the hemagglutinin gene sequences of 197 influenza B strains circulating in both Southern (Sicily) and Northern (Liguria) Italy between 2010 and 2015. Upper respiratory tract specimens of patients displaying symptoms of influenza-like illness were screened by real-time RT-PCR assay for the presence of influenza B virus. PCR-positive influenza B samples were further analyzed by sequencing. Neighbor-joining phylogenetic trees were constructed and the amino-acid alignments were analyzed. Phylogenetic analysis showed clusters in B/Victoria clade 1A/1B (n = 29, 14.7%), and B/Yamagata clades 2 (n = 112, 56.8%) and 3 (n = 56, 28.4%). Both influenza B lineages were found to co-circulate during the study period, although a lineage swap from B/Victoria to B/Yamagata occurred in Italy between January 2011 and January 2013. The most represented amino-acid substitutions were N116K in the 120-loop (83.9% of B/Yamagata clade 3 strains) and I146V in the 150-loop (89.6% of B/Victoria clade 1 strains). D197N in 190-helix was found in almost all viruses collected. Our findings provide further evidence to support the adoption of quadrivalent influenza vaccines in our country.

Ten years (2004-2014) of influenza surveillance in Northern Italy

As the regional influenza reference centre operating within the Italian network InfluNet, here we report data on virological and epidemiological surveillance of influenza, as well as on the vaccination coverage rates achieved in Lombardy (Northern Italy) over 10 consecutive winter seasons (2004-2014).   Over the past 10 years, influenza vaccine coverage declined both in the general population (from 15.7% in 2004-2005 to 11.7% in 2013-2014) and in the vaccine-target population of individuals ≥65-y-of-age (from 65.3% in 2004-2005 to 48.6% in 2013-2014) and is far below the minimum planned threshold level (75%). The highest influenza-like illness (ILI) rates were recorded during the 2004-2005 and 2009-2010 epidemics (peak incidence: 12.04‰ and 13.28‰, respectively). Both seasons were characterised by the introduction of novel viral strains: A/Fujian/411/2002(H3N2) (a drifted hemagglutinin variant) and A/California/7/2009(H1N1) pandemic virus (a swine origin quadruple reassortant), respectively. Because the antigenic match between vaccine and circulating strains was good in both of these seasons, a relevant proportion of cases may have been prevented by vaccination. A different situation was observed during the 2011-2012 season, when ILI morbidity rates in individuals ≥65-y-of-age were 1.5-6-fold higher than those registered during the other epidemics under review. The higher morbidity resulted from the circulation during the 2011-2012 season of an A/Victoria/361/2011(H3N2)-like variant that presented a reduced genetic match with the A(H3N2) strain included in the 2011-2012 vaccine composition. The continuous surveillance of the characteristics of circulating viruses is an essential tool for monitoring their matching with seasonal vaccine strains. Strategies to increase coverage rates are warranted.

Antibody responses to intradermal or intramuscular MF59-adjuvanted influenza vaccines as evaluated in elderly institutionalized volunteers during a season of partial mismatching between vaccine and circulating A(H3N2) strains

Background

The age-related weakening of the immune system makes elderly subjects less responsive to influenza vaccination. In the last years, two “enhanced vaccines” were licensed for individuals aged ≥65 years, one being a subunit vaccine (Fluad®) containing the MF59 adjuvant administered intramuscularly (IM-MF59) and the other one a split non-adjuvanted vaccine administered intradermally (Intanza® 15mcg) (ID). In the present study, we evaluated and compared the antibody responses against the three vaccine antigens and heterovariant A(H3N2) circulating viruses induced by IM-MF59 and ID influenza vaccines in 80 elderly institutionalized volunteers (40 per group) during the Winter season 2011–2012.

Results

Hemagglutination inhibiting (HI) antibody titers were assessed in blood samples collected before, 1 and 6 months after vaccination. One month after vaccination both the IM-MF59 and ID vaccines induced increases in HI titers against all the three vaccine strains. The results in the two groups were similar against the A(H3N2) and A(H1N1) strains. Responses against the B strain typically tended to be higher after ID than IM-MF59, yet both vaccines stimulated lower responses against the B strain than against the two A strains. The two vaccines induced favorable results also against four epidemic drifted A(H3N2) viruses circulating in Winter 2011–2012. Six months after vaccination, the HI titers decreased in both groups.

Conclusion

The responses induced by IM-MF59 and ID vaccines in institutionalized elderly people were similar against the A(H3N2) and A(H1N1) strains but frequently higher, for the ID, against the B strain. The two vaccines induced positive responses against drifted A(H3N2) circulating viruses.

Integrating influenza antigenic dynamics with molecular evolution

Influenza viruses undergo continual antigenic evolution allowing mutant viruses to evade host immunity acquired to previous virus strains. Antigenic phenotype is often assessed through pairwise measurement of cross-reactivity between influenza strains using the hemagglutination inhibition (HI) assay. Here, we extend previous approaches to antigenic cartography, and simultaneously characterize antigenic and genetic evolution by modeling the diffusion of antigenic phenotype over a shared virus phylogeny. Using HI data from influenza lineages A/H3N2, A/H1N1, B/Victoria and B/Yamagata, we determine patterns of antigenic drift across viral lineages, showing that A/H3N2 evolves faster and in a more punctuated fashion than other influenza lineages. We also show that year-to-year antigenic drift appears to drive incidence patterns within each influenza lineage. This work makes possible substantial future advances in investigating the dynamics of influenza and other antigenically-variable pathogens by providing a model that intimately combines molecular and antigenic evolution.

DOI:http://dx.doi.org/10.7554/eLife.01914.001

Every year, seasonal influenza, commonly called flu, infects up to one in five people around the world, and causes up to half a million deaths. Even though the human immune system can detect and destroy the virus that causes influenza, people can catch flu many times throughout their lifetimes because the virus keeps evolving in an effort to avoid the immune system. This antigenic drift—so-called because the antigens displayed by the virus keep changing—also explains why influenza vaccines become less effective over time and need to be reformulated every year.

It is possible to determine which antigens are displayed by a new strain of the virus by observing how blood samples that respond to known strains respond to the new strain. This information about the “antigenic phenotype” of the virus can be plotted on an antigenic map in which strains with similar antigens cluster together. Gene sequencing has shown that there are four subtypes of the flu virus that commonly infect people; but the relationship between changes in antigenic phenotype and changes in gene sequences of the influenza virus is poorly understood.

Bedford et al. have now developed an approach to combine antigenic maps with genetic information about the four subtypes of the human flu virus. This revealed that the antigenic phenotype of H3N2—a subtype that is becoming increasingly common—evolved faster than the other three subtypes. Further, a correlation was observed between antigenic drift and the number of new influenza cases per year for each flu strain. This suggests that knowing which antigenic phenotypes are present at the start of flu season could help predict which strains of the virus will predominate later on.

The work of Bedford et al. provides a useful framework to study influenza, and could help to pinpoint which changes in viral genes cause the changes in antigens. This information could potentially speed up the development of new flu vaccines for each flu season.

DOI:http://dx.doi.org/10.7554/eLife.01914.002

Modified vaccinia virus Ankara expressing the hemagglutinin of pandemic (H1N1) 2009 virus induces cross-protective immunity against Eurasian 'avian-like' H1N1 swine viruses in mice

Objectives

To examine cross-reactivity between hemagglutinin (HA) derived from A/California/7/09 (CA/09) virus and that derived from representative Eurasian “avian-like” (EA) H1N1 swine viruses isolated in Italy between 1999 and 2008 during virological surveillance in pigs.

Design

Modified vaccinia virus Ankara (MVA) expressing the HA gene of CA/09 virus (MVA-HA-CA/09) was used as a vaccine to investigate cross-protective immunity against H1N1 swine viruses in mice.

Sample

Two classical swine H1N1 (CS) viruses and four representative EA-like H1N1 swine viruses previously isolated during outbreaks of respiratory disease in pigs on farms in Northern Italy were used in this study.

Setting

Female C57BL/6 mice were vaccinated with MVA/HA/CA/09 and then challenged intranasally with H1N1 swine viruses.

Main outcome measures

Cross-reactive antibody responses were determined by hemagglutination- inhibition (HI) and virus microneutralizing (MN) assays of sera from MVA-vaccinated mice. The extent of protective immunity against infection with H1N1 swine viruses was determined by measuring lung viral load on days 2 and 4 post-challenge.

Results and Conclusions

Systemic immunization of mice with CA/09-derived HA, vectored by MVA, elicited cross-protective immunity against recent EA-like swine viruses. This immune protection was related to the levels of cross-reactive HI antibodies in the sera of the immunized mice and was dependent on the similarity of the antigenic site Sa of H1 HAs. Our findings suggest that the herd immunity elicited in humans by the pandemic (H1N1) 2009 virus could limit the transmission of recent EA-like swine HA genes into the influenza A virus gene pool in humans.

Neuraminidase inhibitors for influenza B virus infection: efficacy and resistance

Many aspects of the biology and epidemiology of influenza B viruses are far less studied than for influenza A viruses, and one of these aspects is efficacy and resistance to the clinically available antiviral drugs, the neuraminidase (NA) inhibitors (NAIs). Acute respiratory infections are one of the leading causes of death in children and adults, and influenza is among the few respiratory infections that can be prevented and treated by vaccination and antiviral treatment. Recent data has suggested that influenza B virus infections are of specific concern to pediatric patients because of the increased risk of severe disease. Treatment of influenza B is a challenging task for the following reasons: This review presents current knowledge of the efficacy of NAIs for influenza B virus and antiviral resistance in clinical, surveillance, and experimental studies.

Surveillance of influenza viruses in the post-pandemic era (2010-2012) in Northern Italy

The activity and circulation of influenza viruses in Lombardy - Northern Italy - (a region with nearly 10 out of the 60 million inhabitants of Italy) were investigated during two consecutive seasons (2010-2011 and 2011-2012), as part of the Italian Influenza Surveillance Network. The molecular characteristics of the hemagglutinin (HA) sequence of circulating viruses were analyzed to investigate the emergence of influenza viral variants. In the surveyed area, the influenza activity of these two post-pandemic seasons was similar in terms of both time frame and impact. The timing of the influenza epidemics was similar to the timing seen prior to the emergence of the pandemic A(H1N1) virus in 2009. A(H1N1)pdm09 was the predominant virus circulating during the 2010-2011 post-pandemic season and then--unexpectedly--almost disappeared. The HA sequences of these A(H1N1)pdm09 viruses segregated in a different genetic group with respect to those identified during the 2009 pandemic, although they were still closely related to the vaccine viral strain A/California/07/2009. Influenza A(H3N2) viruses were the predominant viruses circulating during the 2011-2012 season, accounting for nearly 88% of influenza viruses identified. All HA sequences of the A(H3N2) viruses isolated in the 2011-2012 season fell into the A/Victoria/208/2009 genetic clade (although the A/Perth/16/2009 virus was the reference vaccine strain). B viruses presented with a mixed circulation of viral variants during these two seasons: viruses belonging to both B/Victoria and B/Yamagata lineages co-circulated in different proportions, with a notable rise in the proportion of B/Yamagata viruses (B/Wisconsin/1/2010-like) during the 2011-2012 epidemic. In conclusion, the continuous monitoring of the characteristics of circulating viruses is an essential tool for understanding the epidemiological and virological features of influenza viruses, for monitoring their matching with seasonal vaccine strains, and for tuning vaccination strategies.

Characterization of glycan binding specificities of influenza B viruses with correlation with hemagglutinin genotypes and clinical features

The carbohydrate binding specificities are different among avian and human influenza A viruses and may affect the tissue tropism and transmission of these viruses. The glycan binding biology for influenza B, however, has not been systematically characterized. Glycan binding specificities of influenza B viral isolates were analyzed and correlated to hemagglutinin (HA) genotypes and clinical manifestations. A newly developed solution glycan array was applied to characterize the receptor binding specificities of influenza B virus clinical isolates from 2001 to 2007 in Taiwan. Thirty oligosaccharides which include α-2,3 and α-2,6 linkage glycans were subjected to analysis. The glycan binding patterns of 53 influenza B isolates could be categorized into three groups and were well correlated to their HA genotypes. The Yamagata-like strains predominantly bound to α-2,6-linkage glycan (24:29, 83%) while Victoria-like strains preferentially bound to both α-2,3- and α-2,6-linkage glycans (13:24, 54%). A third group of viruses bound to sulfated glycans and these all belonged to Victoria-like strains. Based on the HA sequences, Asn-163, Glu-198, Ala-202, and Lys-203 were conserved among Victoria-like strains which may influence their carbohydrate recognition. The viruses bound to dual type glycans were more likely to be associated with the development of bronchopneumonia and gastrointestinal illness than those bound only to α-2,6 sialyl glycans (P < 0.05). Glycan binding analyses provide additional information to monitor the antigenic shift, tissue tropism, and transmission capability of influenza B viruses, and will contribute to virus surveillance and vaccine strain selection.

Can preening contribute to influenza A virus infection in wild waterbirds?

Wild aquatic birds in the Orders Anseriformes and Charadriiformes are the main reservoir hosts perpetuating the genetic pool of all influenza A viruses, including pandemic viruses. High viral loads in feces of infected birds permit a fecal-oral route of transmission. Numerous studies have reported the isolation of avian influenza viruses (AIVs) from surface water at aquatic bird habitats. These isolations indicate aquatic environments have an important role in the transmission of AIV among wild aquatic birds. However, the progressive dilution of infectious feces in water could decrease the likelihood of virus/host interactions. To evaluate whether alternate mechanisms facilitate AIV transmission in aquatic bird populations, we investigated whether the preen oil gland secretions by which all aquatic birds make their feathers waterproof could support a natural mechanism that concentrates AIVs from water onto birds' bodies, thus, representing a possible source of infection by preening activity. We consistently detected both viral RNA and infectious AIVs on swabs of preened feathers of 345 wild mallards by using reverse transcription–polymerase chain reaction (RT-PCR) and virus-isolation (VI) assays. Additionally, in two laboratory experiments using a quantitative real-time (qR) RT-PCR assay, we demonstrated that feather samples (n = 5) and cotton swabs (n = 24) experimentally impregnated with preen oil, when soaked in AIV-contaminated waters, attracted and concentrated AIVs on their surfaces. The data presented herein provide information that expands our understanding of AIV ecology in the wild bird reservoir system.

First case in Italy of acquired resistance to oseltamivir in an immunocompromised patient with influenza A/H1N1v infection

A pandemic influenza A/H1N1v strain with the neuraminidase H274Y mutation was detected in nasal secretions of a 2-year-old leukemic patient with influenza-like illness after 18 days of treatment with oseltamivir. At baseline, no drug-resistant virus was found, while 4 days after treatment initiation a mixture of wild-type and mutated virus was detected. After treatment interruption, the wild type influenza virus re-emerged and became prevalent in nasal secretions after a few days, suggesting the lower fitness of the mutated virus strain. The patient slowly improved concurrently with a decrease in virus load, which resulted negative 42 days after diagnosis. No other drug-resistant influenza A/H1N1v virus strains have been detected in Italy (up to the end of November 2009) since the first case of the novel A/H1N1v virus was identified in the country (May 2009).

Viral causes of influenza-like illness: Insight from a study during the winters 2004-2007

Limited information is available on the viral etiology of influenza-like illness in southern European countries, and it is still a matter of debate whether certain symptoms can be used to distinguish among the specific viruses that cause influenza-like illness. The main objective of the present study was to identify the demographic and clinical predictors of influenza-like illness due to specific viral agents. The study, which was observational in design, was conducted in Rome and Naples, Italy. Cases of influenza-like illness were defined as individuals with fever >37.5 degrees C and at least one systemic and one respiratory symptom, recruited during the winters of 2004-2005, 2005-2006, and 2006-2007. Influenza and other respiratory viruses were identified using the polymerase chain reaction (PCR), performed on throat swabs. Basic individual information was collected using a standard form. A total of 580 persons were included in the analysis. Viral pathogens were identified in fewer than 50% of the cases. Overall, 240 viral agents were detected: 22.8% were positive for influenza viruses, 10.9% for adenoviruses, 6.0% for parainfluenza viruses, and 1.7% for respiratory syncytial virus. The month of diagnosis, and muscle and joint pain were associated with influenza virus, though the positive predictive value (PPV) was low. Abdominal pain was associated with adenovirus infection. Although the PPV of symptoms for influenza virus infection was low, especially in low activity periods, these findings may help clinicians to improve their ability to perform diagnoses.

Cross-reactive antibodies in middle-aged and elderly volunteers after MF59-adjuvanted subunit trivalent influenza vaccine against B viruses of the B/Victoria or B/Yamagata lineages

This study evaluated whether MF59-adjuvanted subunit trivalent influenza vaccine for the 2003/04 winter season (A/Moscow/10/99, H3N2; A/New Caledonia/20/99, H1N1; B/Hong Kong/330/01) would confer protection against mismatched and frequently co-circulating variants of influenza B/Victoria- and B/Yamagata-like virus strains. Haemagglutination inhibiting (HI) antibodies were measured in middle-aged and elderly volunteers against the homologous B/Victoria-like vaccine strain (B/Hong Kong/330/01) and against mismatched B/Victoria-like (B/Malaysia/2506/04) and B/Yamagata-like (B/Singapore/379/99 and B/Shanghai/361/02) strains. Immunization induced significant increases in the amounts of HI antibodies against all influenza B strains under investigation. However, the responses against the heterologous B/Shanghai/361/02 virus did not reach the desirable values of seroprotection. An age-dependent decline of the responses was found for B/Victoria-like antigens, but not for B/Yamagata-like strains. Although further studies are needed, our data support the recommendation of including influenza B viruses of the B/Victoria and B/Yamagata lineages in the future influenza vaccine preparations.

Virological investigation of four outbreaks of influenza B reassortants in the northern region of Taiwan from October 2006 to February 2007

Background

From October 2006 to February 2007, clinical specimens from 452 patients with symptoms related to respiratory tract infection in the northern region of Taiwan were collected. Real-time PCR and direct immunofluorescent antibody tests showed that 145 (32%) patients had influenza B virus infections. Subsequently, nucleotide sequence analyses of both hemagglutinin (HA) and neuraminidase (NA) genes of 39 isolates were performed. Isolated viruses were antigenically characterized using hemagglutinin inhibition (HI) test.

Findings

Phylogenetic tree analysis showed that all the isolates belonged to the B reassortant lineage with HA gene belonged to the B/Victoria/2/87 lineage and the NA gene belonged to the B/Yamagata/16/88 lineage. In addition, a group of children aged between 6 to 8 years old resided in Yilan county were infected with a variant strain. Hemagglutinin inhibition (HI) tests confirmed that all the reassortant influenza B viruses were B/Malaysia/2506/04-like viruses. Pre- and post-immunized serum samples from 4 normal volunteers inoculated with 2007 influenza vaccine were evaluated for their HI activity on 6 reassortant B isolates including two variants that we found in the Yilan county. The results demonstrated that after vaccination, all four vaccinees had at least 4-fold increases of their HI titers.

Conclusion

The results indicate that the 2006–2007 seasonal influenza vaccine was effective in stimulating protective immunity against the influenza B variants identified in Yilan county. Continuous surveillance of emerging influenza B variants in the northern region of Taiwan is important for the selection of proper vaccine candidate in the future.

Crystal structure of unliganded influenza B virus hemagglutinin

Here we report the crystal structure of hemagglutinin (HA) from influenza B/Hong Kong/8/73 (B/HK) virus determined to 2.8 A. At a sequence identity of approximately 25% to influenza A virus HAs, B/HK HA shares a similar overall structure and domain organization. More than two dozen amino acid substitutions on influenza B virus HAs have been identified to cause antigenicity alteration in site-specific mutants, monoclonal antibody escape mutants, or field isolates. Mapping these substitutions on the structure of B/HK HA reveals four major epitopes, the 120 loop, the 150 loop, the 160 loop, and the 190 helix, that are located close in space to form a large, continuous antigenic site. Moreover, a systematic comparison of known HA structures across the entire influenza virus family reveals evolutionarily conserved ionizable residues at all regions along the chain and subunit interfaces. These ionizable residues are likely the structural basis for the pH dependence and sensitivity to ionic strength of influenza HA and hemagglutinin-esterase fusion proteins.

Diagnostic microarray for influenza B viruses

The importance of global influenza surveillance using simple and rapid diagnostics has been frequently highlighted. For influenza type B, the need exists for discrimination between the two currently circulating major lineages, represented by virus strains B/Victoria/2/87 and B/Yamagata/16/88, as only one of these lineages is represented in seasonal influenza vaccines. Here, the development and characterization of a low-density DNA microarray (designated BChip) designed to detect and identify the two influenza B lineages is presented. The assay involved multiplex nucleic acid amplification and microarray hybridization of viral RNA. Detection and lineage identification was achieved in less than 8 h. In a study of 62 influenza B virus samples from 19 countries, dating from 1945 to 2005, as well as 5 negative control samples, the assay exhibited 97% sensitivity and 100% specificity. Furthermore, application of a trained artificial neural network to the pattern of relative fluorescence signals resulted in correct lineage assignment for 94% of 50 applicable influenza B viruses, with no false assignments.

Dynamics of antigenic and genetic changes in the hemagglutinins of influenza A/H3N2 viruses of three consecutive seasons (2002/2003 to 2004/2005) in Austria

Human influenza viruses are subject to continuous antigenic drift and this phenomenon poses great problems for the annual production of vaccines which should ideally be manufactured from strains closely matching the predominant strains of the coming influenza season. We have investigated the dynamics of antigenic and genetic changes in the hemagglutinins of circulating influenza A/H3N2 strains in three consecutive seasons (2002/2003 to 2004/2005) in Austria by sequence analysis of the HA1 domain and by antigenic characterization using a hemagglutination inhibition assay. Each of the three seasons was dominated by a single and different H3N2 variant, but in all cases sequencing revealed the co-circulation of a drift variant which would have been missed by conventional antigenic analysis. These emerging strains always showed already a close genetic relationship to the dominating strain of the following season. Our results underscore the value of monitoring seasonal influenza strain dynamics by sequence analysis as an instrument that can provide important and timely information on the appearance of strains with epidemiologic significance.

Safety, efficacy, and effectiveness of cold-adapted influenza vaccine-trivalent against community-acquired, culture-confirmed influenza in young children attending day care

OBJECTIVE

The goal was to evaluate the safety, tolerability, and efficacy of an investigational, refrigerator-stable formulation of live attenuated influenza vaccine (cold-adapted influenza vaccine-trivalent) against culture-confirmed influenza, acute otitis media, and effectiveness outcomes in young children in day care over 2 consecutive influenza seasons.

METHODS

Children 6 to <36 months of age who were attending day care were assigned randomly in year 1 to receive 2 doses of vaccine or placebo intranasally, 35 +/- 7 days apart. In year 2, subjects received 1 dose of the same treatment as in year 1.

RESULTS

A total of 1616 subjects (vaccine: 951 subjects; placebo: 665 subjects) in year 1 and 1090 subjects (vaccine: 640 subjects; placebo: 450 subjects) in year 2 were able to be evaluated for efficacy. The mean age at first vaccination was 23.4 +/- 7.9 months. In year 1, the overall efficacy of the vaccine against influenza subtypes similar to the vaccine was 85.4%; efficacy was 91.8% against A/H1N1 and 72.6% against B. In year 2, the overall efficacy was 88.7%; efficacy was 90.0% against H1N1, 90.3% against A/H3N2, and 81.7% against B. Efficacy against all episodes of acute otitis media associated with culture-confirmed influenza was 90.6% in year 1 and 97.0% in year 2. Runny nose or nasal discharge after dose 1 in year 1 was the only reactogenicity event that was significantly more frequent with cold-adapted influenza vaccine-trivalent (82.3%) than placebo (75.4%).

CONCLUSIONS

Cold-adapted influenza vaccine-trivalent was well tolerated and effective in preventing culture-confirmed influenza illness in children as young as 6 months of age who attended day care.

Increasing appearance of reassortant influenza B virus in Taiwan from 2002 to 2005

Genetic and antigenic analyses of influenza B virus field strains isolated in Taiwan from 1998 to 2005 were performed. To investigate the molecular evolution of influenza B viruses, sequence analysis of the hemagglutinin (HA1 subunit) and neuraminidase genes was performed. All influenza B viruses isolated between 1998 and 2000 belonged to the B/Yamagata/16/88 lineage. The B/Victoria/2/87 lineage, which was cocirculating with the Yamagata lineage, was identified in Taiwan in March 2001. Concurrently, there was an increasing prevalence of this lineage in many parts of the world, including North America and Europe, during the 2001-2002 season. Since 2002, genetic reassortants of influenza B virus with the Victoria lineage of hemagglutinin and the Yamagata lineage of neuraminidase have been found at a rate of 46%. Therefore, in 2002, at least three sublineages of influenza B virus strains, the B/Shanghai/361/2002-like strain (Yamagata lineage), the B/Hong Kong/330/01-like strain (Victoria lineage), and the B/Hong Kong/1351/02-like strain (B reassortant lineage), were identified in Taiwan. The results showed that genetically distinct lineages can cocirculate in the population and that the reassortment among these strains plays a role in generating the genetic diversity of influenza B viruses. Interestingly, from January to April 2005, B reassortant viruses became dominant (73%) in Taiwan, which indicated that a mismatch had occurred between the influenza B vaccine strain recommended for the 2004-2005 season in the Northern hemisphere by the World Health Organization and the epidemic strain.

Molecular analysis of isolates from influenza B outbreaks in the U.S. and Nepal, 2005

Currently circulating influenza B viruses can be divided into two antigenically and genetically distinct lineages referred to by their respective prototype strains, B/Yamagata/16/88 and B/Victoria/2/87, based on amino acid differences in the hemagglutinin surface glycoprotein. During May and July 2005, clinical specimens from two early season influenza B outbreaks in Arizona and southeastern Nepal were subjected to antigenic (hemagglutinin inhibition) and nucleotide sequence analysis of hemagglutinin (HA1), neuraminidase (NA), and NB genes. All isolates exhibited little reactivity with the B/Shanghai/361/2002 (B/Yamagata-like) vaccine strain and significantly reduced reactivity with the previous 2003/04 B/Hong Kong/330/2001 (B/Victoria-like) vaccine strain. The majority of isolates were antigenically similar to B/Hawaii/33/2004, a B/Victoria-like reference strain. Sequence analysis indicated that 33 of 34 isolates contained B/Victoria-like HA and B/Yamagata-like NA and NB proteins. Thus, these outbreak isolates are both antigenically and genetically distinct from the current Northern Hemisphere vaccine virus strain as well as the previous 2003-04 B/Hong Kong/330/2001 (B/Victoria lineage) vaccine virus strain but are genetically similar to B/Malaysia/2506/2004, the vaccine strain proposed for the coming seasons in the Northern and Southern Hemispheres. Since these influenza B outbreaks occurred in two very distant geographical locations, these viruses may continue to circulate during the 2006 season, underscoring the importance of rapid molecular monitoring of HA, NA and NB for drift and reassortment.