Two outbreaks of influenza A (H3N2) in a Japanese nursing home in the winter of 1996-1997, with differing vaccine efficacy.
Sixty of 128 (46.9%) residents of a nursing home were immunized with two doses of the trivalent split influenza vaccine. They developed 7.4-11.5-fold antibody increases, with a 69-82% protection rate, presenting good immune response rates to the influenza vaccine. Two outbreaks of influenza A (H3N2) occurred. There were no significant antigenic differences among the vaccine strain and the strains isolated from both outbreaks in haemagglutination-inhibition tests, suggesting that the second might have been a reoccurrence. There were no residents who were infected in both outbreaks. The vaccine efficacy against clinical illness in the first outbreak of typical influenza-like-illness (ILI) was 51% (relative risk: 0.49), and the febrile period was reduced significantly by vaccination. In the second outbreak, however, in which all patients had atypical ILI with a high fever but not respiratory symptoms, vaccine efficacy was not apparent for unknown reason. (+info)
Laboratory characteristics of an attenuated influenza type A (H3N2) virus ('Alice' strain).
The Alice strain of live attenuated influenza virus was obtained by selection of a gamma inhibitor-resistant strain from a virus recombinant between A/PR/8/34 (HON1) and A/England/42/72 (H3N2). Its behaviour in vitro and in vivo was studied. Three marker systems were investigated: resistance to serum inhibitors, growth capacity at high temperature and low sensitivity to amantadine hydrochloride. In ferrets the strain was found to be attenuated and immunogenic. Passages in man, animals and eggs have not affected its resistance to gamma inhibitors. (+info)
Efficacy of influenza vaccine in the elderly in welfare nursing homes: reduction in risks of mortality and morbidity during an influenza A (H3N2) epidemic.
The effect of influenza vaccination on the occurrence and severity of influenza virus infection in a population residing in nursing homes for the elderly was studied during an influenza A (H3N2) epidemic in Japan. Of 22,462 individuals living in 301 welfare nursing homes, 10,739 received either one dose (2027 subjects) or two doses (8712 subjects) of inactivated, subunit trivalent influenza vaccine. During the period Nov. 1998 to March 1999, there were 950 cases of influenza infection diagnosed clinically, with virus isolation or serology. There were statistically significantly fewer cases of influenza, hospital admissions due to severe infection and deaths due to influenza in the vaccinated cohort (256 cases, 32 hospital admissions, 1 death) than in the unvaccinated controls (694 cases, 150 hospital admissions, 5 deaths; reduction rates 59.8%, 76.9% and 79.1% respectively). Vaccination was almost equally effective in those who received one dose of vaccine and those who received two doses. No serious adverse reactions to vaccination were recorded. Thus influenza vaccination is safe and effective in this population, and should be an integral part of the routine care of persons aged > or =65 years residing in nursing homes. (+info)
A simple restriction fragment length polymorphism-based strategy that can distinguish the internal genes of human H1N1, H3N2, and H5N1 influenza A viruses.
A simple molecular technique for rapid genotyping was developed to monitor the internal gene composition of currently circulating influenza A viruses. Sequence information from recent H1N1, H3N2, and H5N1 human virus isolates was used to identify conserved regions within each internal gene, and gene-specific PCR primers capable of amplifying all three virus subtypes were designed. Subtyping was based on subtype-specific restriction fragment length polymorphism (RFLP) patterns within the amplified regions. The strategy was tested in a blinded fashion using 10 control viruses of each subtype (total, 30) and was found to be very effective. Once standardized, the genotyping method was used to identify the origin of the internal genes of 51 influenza A viruses isolated from humans in Hong Kong during and immediately following the 1997-1998 H5N1 outbreak. No avian-human or H1-H3 reassortants were detected. Less than 2% (6 of 486) of the RFLP analyses were inconclusive; all were due to point mutations within a restriction site. The technique was also used to characterize the internal genes of two avian H9N2 viruses isolated from children in Hong Kong during 1999. (+info)
Antigenic drift in the influenza A virus (H3N2) nucleoprotein and escape from recognition by cytotoxic T lymphocytes.
Viruses exploit different strategies to escape immune surveillance, including the introduction of mutations in cytotoxic T-lymphocyte (CTL) epitopes. The sequence of these epitopes is critical for their binding to major histocompatibility complex (MHC) class I molecules and recognition by specific CTLs, both of which interactions may be lost by mutation. Sequence analysis of the nucleoprotein gene of influenza A viruses (H3N2) isolated in The Netherlands from 1989 to 1999 revealed two independent amino acid mutations at the anchor residue of the HLA-B27-specific CTL epitope SRYWAIRTR (383 to 391). A R384K mutation was found in influenza A viruses isolated during the influenza season 1989-1990 but not in subsequent seasons. In the influenza season 1993-1994, a novel mutation in the same CTL epitope at the same position was introduced. This R384G mutation proved to be conserved in all influenza A viruses isolated from 1993 onwards. Both mutations R384K and R384G abrogated MHC class I presentation and allowed escape from recognition by specific CTLs. (+info)
Evolution of swine H3N2 influenza viruses in the United States.
During 1998, severe outbreaks of influenza were observed in four swine herds in the United States. This event was unique because the causative agents, H3N2 influenza viruses, are infrequently isolated from swine in North America. Two antigenically distinct reassortant viruses (H3N2) were isolated from infected animals: a double-reassortant virus containing genes similar to those of human and swine viruses, and a triple-reassortant virus containing genes similar to those of human, swine, and avian influenza viruses (N. N. Zhou, D. A. Senne, J. S. Landgraf, S. L. Swenson, G. Erickson, K. Rossow, L. Liu, K.-J. Yoon, S. Krauss, and R. G. Webster, J. Virol. 73:8851-8856, 1999). Because the U.S. pig population was essentially naive in regard to H3N2 viruses, it was important to determine the extent of viral spread. Hemagglutination inhibition (HI) assays of 4, 382 serum samples from swine in 23 states indicated that 28.3% of these animals had been exposed to classical swine-like H1N1 viruses and 20.5% had been exposed to the triple-reassortant-like H3N2 viruses. The HI data suggested that viruses antigenically related to the double-reassortant H3N2 virus have not become widespread in the U.S. swine population. The seroreactivity levels in swine serum samples and the nucleotide sequences of six additional 1999 isolates, all of which were of the triple-reassortant genotype, suggested that H3N2 viruses containing avian PA and PB2 genes had spread throughout much of the country. These avian-like genes cluster with genes from North American avian viruses. The worldwide predominance of swine viruses containing an avian-like internal gene component suggests that these genes may confer a selective advantage in pigs. Analysis of the 1999 swine H3N2 isolates showed that the internal gene complex of the triple-reassortant viruses was associated with three recent phylogenetically distinct human-like hemagglutinin (HA) molecules. Acquisition of HA genes from the human virus reservoir will significantly affect the efficacy of the current swine H3N2 vaccines. This finding supports continued surveillance of U.S. swine populations for influenza virus activity. (+info)
Change in receptor-binding specificity of recent human influenza A viruses (H3N2): a single amino acid change in hemagglutinin altered its recognition of sialyloligosaccharides.
Human H3N2 influenza A viruses were known to preferentially bind to sialic acid (SA) in alpha2,6Gal linkage on red blood cells (RBC). However, H3N2 viruses isolated in MDCK cells after 1992 did not agglutinate chicken RBC (CRBC). Experiments with point-mutated hemagglutinin (HA) of A/Aichi/51/92, one of these viruses, revealed that an amino acid change from Glu to Asp at position 190 (E190D) was responsible for the loss of ability to bind to CRBC. A/Aichi/51/92 did not agglutinate CRBC treated with alpha2, 3-sialidase, suggesting that SAalpha2,3Gal on CRBC might not inhibit the binding of the virus to SAalpha2,6Gal on CRBC. However, the virus agglutinated derivatized CRBC resialylated with SAalpha2, 6Galbeta1,4GlcNAc. These findings suggested that the E190D change might have rendered the HA able to distinguish sialyloligosaccharides on the derivatized CRBC containing the SAalpha2,6Galbeta1,4GlcNAc sequence from those on the native CRBC. (+info)
Two cases of severe bronchopneumonia due to influenza A (H3N2) virus: detection of influenza virus gene using reverse transcription polymerase chain reaction.
We report two cases of severe bronchopneumonia due to influenza A (H3N2) virus. The severity of the disease necessitated initiation of empiric therapy based on the present illness and clinical data on admission. Both patients were improved by artificial ventilation with positive end-expiratory pressures and administration of broad spectrum antibiotics and corticosteroids before confirming the diagnosis of viral bronchopneumonia using viral culture and serological tests. Within 24 hours, influenza A (H3N2) virus was identified by amplification of the pathogen genes by reverse transcription polymerase chain reaction (RT-PCR) using the stored bronchoalveolar lavage (BAL) fluids of both cases. This suggests that a combination of detection methods of pathogens using RT-PCR and BAL fluid will facilitate determination of rational treatment aimed at influenza A virus. (+info)