Recent influenza B viruses in Europe: a phylogenetic analysis

Comparison of two vaccination programmes in preventing influenza-related hospitalization among the elderly during two consecutive seasons

The protective effect of influenza vaccine against influenza related hospitalization is well established at an individual level, but the effect of vaccination programme at the population level is unknown. In this study we compared a risk disease-based free-of-charge influenza vaccination programme in preventing hospitalizations due to influenza or pneumonia and cardiovascular diseases during 2 consecutive influenza seasons 1992/93 and 1993/94 in 43 municipalities in northern Finland. Vaccinations were carried out and reported by local staff in health centres. Data of hospital treatment periods were obtained from the National Hospital Discharge Register. During the influenza seasons the number of hospitalizations due to cardiovascular diseases and influenza/pneumonia increased by 13%. In the 1993/1994 season the increase in the study area with the risk disease-based vaccination programme was 22 per 1000 persons (95% CI 19-24), and with an age-based programme 3.3 per 1000 persons (95% CI 2.5-4.0), while the increase in the 1992/1993 season in both areas was 3-4 per 1000. The excess of hospitalization related to influenza epidemics is mostly due to cardiovascular diseases and varies from y to y, as do the benefits gained by vaccination.

Quantifying influenza vaccine efficacy and antigenic distance

We introduce a new measure of antigenic distance between influenza A vaccine and circulating strains. The measure correlates well with efficacies of the H3N2 influenza A component of the annual vaccine between 1971 and 2004, as do results of a theory of the immune response to influenza following vaccination. This new measure of antigenic distance is correlated with vaccine efficacy to a greater degree than are current state of the art phylogenetic sequence analyses or ferret antisera inhibition assays. We suggest that this new measure of antigenic distance be used in the design of the annual influenza vaccine and in the interpretation of vaccine efficacy monitoring.

Evolution of surface and nonstructural-1 genes of influenza B viruses isolated in the Province of Québec, Canada, during the 1998-2001 period

After 2 minor winter seasons, influenza B viruses were predominantly isolated in the Province of Quebec, Canada, during the 2000-2001 season representing 74% of laboratory-confirmed influenza viruses. We performed an antigenic study of the hemagglutinin (HA) protein and a molecular characterization of the HA1 region, nonstructural-1 (NS1) and neuraminidase (NA)/NB genes of 20 influenza B strains isolated in the Province of Quebec during the 1998-2001 period. Our isolates were compared to recent vaccine strains (B/Harbin/7/94 in 1998-1999, B/Yamanashi/166/98 in 1999-2000 and 2000-2001, and B/Sichuan/379/99 in 2001-2002). The hemagglutination inhibition (HI) test revealed that all isolates were different from B/Harbin/7/94 and were more related to the 2 other vaccine strains although precise identification was often impossible. Molecular analysis of the HA1 gene revealed that both B/Yamanashi/166/98-like and B/Sichuan/379/99-like isolates co-circulated during the 1998-1999 season whereas isolates from the 2 subsequent years were more related to B/Sichuan/379/99. Most isolates (8/9) of the 2000-2001 season contained a N126D substitution recently associated with altered antigenicity in recent influenza B/Yamagata/16/88-related viruses. Although the HA1 and NS1 protein sequences of viruses isolated during the 1998-1999 season were clearly different from those of the respective vaccine strain (B/Harbin/7/94), the NA protein sequence of those isolates was slightly more related to B/Harbin/7/94 than B/Yamanashi/166/98 suggesting distinct patterns of evolution for these genes. This study confirms the importance of a detailed molecular analysis for understanding the evolution of influenza B viruses.

Genetic characterization of the hemagglutinin of two strains of influenza B virus co-circulated in Taiwan

Two isolates of influenza B virus were obtained in the spring of 1997. One strain, B/Taiwan/21706/97, was isolated from a patient who had acute tonsillitis. The other, B/Taiwan/3143/97, was isolated from a patient who was diagnosed with meningoencephalitis. This implies that the influenza B viruses not only cause respiratory symptoms but may also cause inflammation of the nervous system. Sequence analysis of the hemagglutinin (HA) gene, HA1 domain, indicated that there were remarkable amino acid changes in the strain B/Taiwan/3143/97 compared to B/Victoria/2/87, B/Yamagata/16/88, and B/Taiwan/7/88. The changes in the positions 116, 200, 238, 242, and 271 were correlated with receptor binding. Furthermore, a potential glycosylation site at position 233 was lost. In total, 30 amino acid changes were noted at positions ranging from 116 to 295. These changes may affect the antigenicity of the virus. Phylogenetic analyses also showed that the B/Taiwan/3143/97 was located in an independent lineage, when compared to the reference strains belonging to B/Victoria/2/87 and B/Yamagata/16/88 lineages. This supports the hypothesis that influenza B viruses with distinct genetic characteristic were co-circulated in Taiwan.

Identification of new influenza B virus variants by multiplex reverse transcription-PCR and the heteroduplex mobility assay

A quick genetic approach for the screening of influenza virus variants was developed in this laboratory (S. Zou, J. Clin. Microbiol. 35:2623-2627, 1997). It uses multiplex reverse transcription and multiplex PCR to amplify and differentiate the variable region of the hemagglutinin genes of different types and subtypes of influenza viruses. Variants within the same type or subtype are then identified by the heteroduplex mobility shift assay of the amplicons. The method was used to screen influenza virus isolates received from provincial laboratories during the 1996-1997 season and was able to identify new influenza B virus variants. Sequencing of the amplicons derived from the hemagglutinin gene of the identified variants and comparison with the vaccine strain B/Harbin/7/94 showed substitution rates of 2.26 to 2.55% at the nucleotide level and 4.26 to 4.68% at the amino acid level. The result further demonstrated that the approach provides a quick, sensitive, and reliable screening for influenza virus variants. It also suggested the necessity of close monitoring of influenza B virus isolates in the 1997-1998 season and critical evaluation of the reference strain for the type B influenza virus.

A practical approach to genetic screening for influenza virus variants

This report describes a quick genetic approach to the screening of influenza virus variants. Multiplex reverse transcription (MRT) and multiplex PCR (MPCR) were used to amplify and differentiate the hemagglutinin (HA) genes of different types and subtypes of influenza viruses. Heteroduplex mobility assay (HMA) was then used to differentiate strains within the same type and subtype. Three primers complementary to the consensus 3' termini of viral genomic RNA segments of human influenza virus types A, B, and C were used in a single MRT reaction to prime the synthesis of cDNA of all the viral genome segments. The cDNA was then amplified in an MPCR containing primers for the HA genes of the H1 and H3 subtypes of type A, the HA gene of type B, and the counterpart of type C virus. Amplicons of the different types and subtypes differ in size, thus allowing typing and subtyping. The regions amplified cover most of the HA1 portion of the HA genes and therefore amplicons of variants identified by the described HMA can be sequenced directly. In the HMA, the amplicon of an individual strain was mixed with that of a reference strain and heteroduplexes derived from mismatches migrated more slowly than homoduplexes of the same size in electrophoresis, with the mobility shift pattern indicating the divergence of amplicons. The whole process from viral RNA extraction to HMA can be completed within 2 days and thus provides a quick screening before further analysis by hemagglutination inhibition testing and sequencing. In addition, all segments of the viral genome can be amplified from a single MRT reaction, which can yield valuable sources of products for future genetic analyses. This method should facilitate genetic screening and characterization of influenza virus variants.