| 66 | Humans |
| 37 | Animals |
| 31 | Influenza, Human (epidemiology) |
| 21 | Influenza, Human (virology) |
| 20 | Influenza A virus (genetics) |
| 16 | Female |
| 16 | Disease Outbreaks |
| 15 | Molecular Sequence Data |
| 13 | Influenza A virus (immunology) |
| 13 | Adult |
| 12 | Phylogeny |
| 12 | Influenza, Human (prevention & control) |
| 11 | Influenza |
| 11 | Human |
| 10 | Middle Aged |
| 10 | Influenza A Virus, H2N2 Subtype (immunology) |
| 10 | Epidemiology |
| 10 | Birds |
| 10 | Amino Acid Sequence |
| 10 | Aged |
| 10 | Adolescent |
| 9 | Male |
| 9 | Influenza, Human (transmission) |
| 9 | Child, Preschool |
| 8 | Viral Proteins (genetics) |
| 8 | Neuraminidase (genetics) |
| 8 | Influenza A virus (pathogenicity) |
| 8 | Influenza A Virus, H3N2 Subtype |
| 8 | Influenza A Virus, H2N2 Subtype |
| 8 | History, 20th Century |
| 8 | Child |
| 7 | Models, Molecular |
| 7 | Mice |
| 7 | Influenza, Human (history) |
| 7 | Influenza in Birds (virology) |
| 7 | Influenza A virus (physiology) |
| 7 | Infant |
| 7 | Hemagglutinin Glycoproteins, Influenza Virus (genetics) |
| 7 | Hemagglutinin Glycoproteins, Influenza Virus (chemistry) |
| 7 | Antibodies, Viral (blood) |
| 6 | Reassortant Viruses (genetics) |
| 6 | Orthomyxoviridae Infections (virology) |
| 6 | Influenza, Human (immunology) |
| 6 | Influenza in Birds (epidemiology) |
| 6 | Influenza Vaccines (immunology) |
| 6 | Influenza A |
| 6 | Influenza A virus |
| 6 | Influenza A virus (enzymology) |
| 6 | Influenza A virus (classification) |
| 6 | Hemagglutination Inhibition Tests |
| 6 | Base Sequence |
| 5 | Young Adult |
| 5 | Swine |
| 5 | Species Specificity |
| 5 | Pandemics |
| 5 | Orthomyxoviridae Infections (immunology) |
| 5 | Influenza, Human (mortality) |
| 5 | Influenza A virus (isolation & purification) |
| 5 | Influenza A Virus, H2N2 Subtype (genetics) |
| 5 | Hemagglutinin Glycoproteins, Influenza Virus (metabolism) |
| 5 | Ferrets |
| 5 | Evolution, Molecular |
| 5 | Biological Evolution |
| 5 | Antibodies, Viral (immunology) |
| 4 | Zoonoses (virology) |
| 4 | Zoonoses (epidemiology) |
| 4 | Virus Replication |
| 4 | Sequence Analysis, DNA |
| 4 | Sequence Alignment |
| 4 | Protein Binding |
| 4 | Orthomyxoviridae Infections (prevention & control) |
| 4 | Neutralization Tests |
| 4 | Neuraminidase (metabolism) |
| 4 | Neuraminidase (immunology) |
| 4 | Mutation |
| 4 | Mice, Inbred BALB C |
| 4 | Influenza Vaccines (administration & dosage) |
| 4 | Influenza A Virus, H3N2 Subtype (genetics) |
| 4 | Influenza A Virus, H2N2 Subtype (isolation & purification) |
| 4 | Influenza A Virus, H1N1 Subtype |
| 4 | Hong Kong (epidemiology) |
| 4 | Hemagglutinin Glycoproteins, Influenza Virus (immunology) |
| 4 | Epidemic |
| 4 | Dogs |
| 4 | Disease Outbreaks (history) |
| 4 | Cell Line |
| 4 | Amino Acid Substitution |
| 3 | Zoonoses (transmission) |
| 3 | Viral Proteins (chemistry) |
| 3 | United States (epidemiology) |
| 3 | Transmission from animal to man |
| 3 | Swine (virology) |
| 3 | Subtype |
| 3 | Seasons |
| 3 | Receptors, Virus (metabolism) |
| 3 | Orthomyxoviridae (genetics) |
| 3 | Origin |
| 3 | Neuraminidase (chemistry) |
| 3 | Mutation, Missense |
| 3 | Mortality |
| 3 | Models, Biological |
| 3 | Influenzavirus A |
| 3 | Influenza, Human (genetics) |
| 3 | Influenza in Birds (transmission) |
| 3 | Influenza A Virus, H5N1 Subtype (immunology) |
| 3 | Infection |
| 3 | Infant, Newborn |
| 3 | Hydrogen-Ion Concentration |
| 3 | Hong Kong |
| 3 | Hemagglutinins, Viral (immunology) |
| 3 | Exo-α-sialidase |
| 3 | Ducks (virology) |
| 3 | Disease Outbreaks (prevention & control) |
| 3 | Cross Reactions |
| 3 | Cluster Analysis |
| 3 | Chick Embryo |
| 3 | Case history |
| 3 | Antiviral Agents (therapeutic use) |
| 3 | Antibodies, Neutralizing (blood) |
| 3 | Aged, 80 and over |
| 3 | Age |
| 3 | Age Factors |
| 3 | Age Distribution |
| 2 | phylogenetic analysis |
| 2 | influenza virus |
| 2 | Zoonoses |
| 2 | Virulence |
| 2 | Viral Proteins (immunology) |
| 2 | Vaccines, Inactivated (immunology) |
| 2 | Time Factors |
| 2 | Swine Diseases (virology) |
| 2 | Survival Analysis |
| 2 | Spain (epidemiology) |
| 2 | Seroepidemiologic Studies |
| 2 | Sequence Homology, Nucleic Acid |
| 2 | Sequence Homology, Amino Acid |
| 2 | Risk Factors |
| 2 | Risk Assessment |
| 2 | Replication |
| 2 | Reassortant Viruses (immunology) |
| 2 | RNA, Viral (genetics) |
| 2 | Prevalence |
| 2 | Poultry |
| 2 | Poultry Diseases (virology) |
| 2 | Poultry (virology) |
| 2 | Pandemics (prevention & control) |
| 2 | Pandemic |
| 2 | Orthomyxoviridae Infections (veterinary) |
| 2 | Orthomyxoviridae Infections (pathology) |
| 2 | Nucleoproteins (genetics) |
| 2 | Neuraminidase (antagonists & inhibitors) |
| 2 | Mutagenesis, Site-Directed |
| 2 | Molecular evolution |
| 2 | Molecular epidemiology |
| 2 | Models, Genetic |
| 2 | Microbiology |
| 2 | Mammalia |
| 2 | Lung (immunology) |
| 2 | Influenzavirus |
| 2 | Influenza, Human (metabolism) |
| 2 | Influenza, Human (drug therapy) |
| 2 | Influenza in Birds (prevention & control) |
| 2 | Influenza in Birds (history) |
| 2 | Influenza in Birds (genetics) |
| 2 | Influenza Vaccines (therapeutic use) |
| 2 | Influenza Vaccines (adverse effects) |
| 2 | Influenza A virus (growth & development) |
| 2 | Influenza A Virus, H9N2 Subtype (immunology) |
| 2 | Influenza A Virus, H3N2 Subtype (isolation & purification) |
| 2 | Influenza A Virus, H3N2 Subtype (immunology) |
| 2 | Influenza A Virus, H3N2 Subtype (chemistry) |
| 2 | Influenza A Virus, H2N2 Subtype (pathogenicity) |
| 2 | Influenza A Virus, H2N2 Subtype (growth & development) |
| 2 | Influenza A Virus, H1N1 Subtype (immunology) |
| 2 | Influenza A Virus, H1N1 Subtype (genetics) |
| 2 | Immunity |
| 2 | Immune response |
| 2 | Homology |
| 2 | History, Medieval |
| 2 | History, 19th Century |
| 2 | History, 18th Century |
| 2 | History, 17th Century |
| 2 | History, 16th Century |
| 2 | Hemagglutinins, Viral (genetics) |
| 2 | Hemagglutinins, Viral (chemistry) |
| 2 | Hemagglutinin |
| 2 | Healthy Volunteers |
| 2 | Global Health |
| 2 | Genetic reassortment |
| 2 | Genes, Viral |
| 2 | Genes, Viral (genetics) |
| 2 | Gene |
| 2 | Finland |
| 2 | Europe |
| 2 | Enzyme Stability |
| 2 | Ducks |
| 2 | Double-Blind Method |
| 2 | Disease Reservoirs |
| 2 | Disease Models, Animal |
| 2 | Disaster Planning |
| 2 | Crystallography, X-Ray |
| 2 | Cross Reactions (immunology) |
| 2 | Computational Biology |
| 2 | Bird Diseases (virology) |
| 2 | Bird Diseases (transmission) |
| 2 | Binding Sites |
| 2 | Avian influenzavirus |
| 2 | Aves |
| 2 | Asia |
| 2 | Asia (epidemiology) |
| 2 | Antigenic Variation |
| 2 | Antibody |
| 2 | Antibodies, Viral (analysis) |
| 2 | Antibodies, Neutralizing (immunology) |
| 2 | Antibodies, Monoclonal |
| 2 | Antibodies, Monoclonal (immunology) |
| 2 | Algorithms |
| 1 | validation |
| 1 | prediction |
| 1 | neutralization |
| 1 | migratory ducks |
| 1 | migratory duck |
| 1 | mechanism of neutralization |
| 1 | inhibition of internalization |
| 1 | inhibition of fusion |
| 1 | inhibition of attachment |
| 1 | influenza A virus |
| 1 | computational epidemiology |
| 1 | affinity |
| 1 | Zoonoses (history) |
| 1 | Zanamivir |
| 1 | World Health Organization |
| 1 | Winter |
| 1 | Viruses (isolation & purification) |
| 1 | Viruses (classification) |
| 1 | Virus evolution |
| 1 | Virus Replication (physiology) |
| 1 | Virus Replication (genetics) |
| 1 | Virus Replication (drug effects) |
| 1 | Virus Diseases (virology) |
| 1 | Virus Diseases (transmission) |
| 1 | Virus Diseases (epidemiology) |
| 1 | Virus Diseases (classification) |
| 1 | Virus Attachment |
| 1 | Virulence (genetics) |
| 1 | Virology |
| 1 | Viral vaccines |
| 1 | Viral Structural Proteins (genetics) |
| 1 | Viral Proteins (physiology) |
| 1 | Viral Proteins (classification) |
| 1 | Viral Nonstructural Proteins (genetics) |
| 1 | Viral Matrix Proteins |
| 1 | Vietnam |
| 1 | Vaccines |
| 1 | Vaccines, Inactivated (pharmacology) |
| 1 | Vaccines, DNA (immunology) |
| 1 | Vaccines, Attenuated |
| 1 | Vaccines, Attenuated (immunology) |
| 1 | Vaccination (statistics & numerical data) |
| 1 | Vaccination (methods) |
| 1 | Vaccination (adverse effects) |
| 1 | Up-Regulation |
| 1 | United States |
| 1 | United Kingdom (epidemiology) |
| 1 | Typing |
| 1 | Tropical Climate |
| 1 | Treatment Outcome |
| 1 | Transmission from animal to animal |
| 1 | Transfection |
| 1 | Thermal stability |
| 1 | Temperature |
| 1 | Tanzania |
| 1 | Taiwan (epidemiology) |
| 1 | T-Lymphocytes (immunology) |
| 1 | Swine Diseases (transmission) |
| 1 | Swine Diseases (epidemiology) |
| 1 | Swine (blood) |
| 1 | Survival |
| 1 | Strain |
| 1 | Stochastic Processes |
| 1 | Species specificity |
| 1 | Social Problems |
| 1 | Sialic Acids (pharmacology) |
| 1 | Sialic Acids (metabolism) |
| 1 | Sequence alignment |
| 1 | Sentinel Surveillance |
| 1 | Sensitivity and Specificity |
| 1 | Selection, Genetic |
| 1 | Season |
| 1 | Seals, Earless |
| 1 | Seals, Earless (virology) |
| 1 | Review |
| 1 | Reverse Transcriptase Polymerase Chain Reaction |
| 1 | Reverse Genetics |
| 1 | Retrospective Studies |
| 1 | Respiratory tract |
| 1 | Respiratory disease |
| 1 | Respiratory Tract Infections (virology) |
| 1 | Respiratory Tract Infections (prevention & control) |
| 1 | Respiratory Tract Infections (pathology) |
| 1 | Respiratory Tract Infections (immunology) |
| 1 | Research |
| 1 | Reproducibility of Results |
| 1 | Recombination, Genetic |
| 1 | Recombinant Fusion Proteins (metabolism) |
| 1 | Receptors, Virus (physiology) |
| 1 | Receptors, Virus (genetics) |
| 1 | Receptors, Cell Surface (metabolism) |
| 1 | Reassortant Viruses |
| 1 | Reassortant Viruses (physiology) |
| 1 | Reassortant Viruses (pathogenicity) |
| 1 | Reassortant Viruses (isolation & purification) |
| 1 | Reassortant Viruses (growth & development) |
| 1 | Reassortant Viruses (enzymology) |
| 1 | Real-Time Polymerase Chain Reaction (methods) |
| 1 | RNA Replicase (genetics) |
| 1 | Pyrans |
| 1 | Protein Structure, Secondary |
| 1 | Property structure relationship |
| 1 | Propagation velocity |
| 1 | Probability |
| 1 | Primary structure |
| 1 | Pregnancy |
| 1 | Pregnancy Complications, Infectious (prevention & control) |
| 1 | Predictive Value of Tests |
| 1 | Poultry Diseases (metabolism) |
| 1 | Poultry Diseases (immunology) |
| 1 | Poultry Diseases (genetics) |
| 1 | Poultry Diseases (blood) |
| 1 | Poultry (growth & development) |
| 1 | Population Surveillance |
| 1 | Population Growth |
| 1 | Polysaccharides (metabolism) |
| 1 | Polysaccharides (chemistry) |
| 1 | Polysaccharides (analysis) |
| 1 | Pneumonia, Viral (prevention & control) |
| 1 | Pneumonia (prevention & control) |
| 1 | Phenotype |
| 1 | Perspective |
| 1 | Pepitope |
| 1 | Pathogenesis |
| 1 | Parvovirus, Canine (physiology) |
| 1 | Parvovirus, Canine (pathogenicity) |
| 1 | Parvovirus, Canine (genetics) |
| 1 | Parvovirus, Canine (chemistry) |
| 1 | Pandemics (history) |
| 1 | Orthomyxoviridae Infections (transmission) |
| 1 | Orthomyxoviridae Infections (mortality) |
| 1 | Orthomyxoviridae Infections (history) |
| 1 | Orthomyxoviridae Infections (genetics) |
| 1 | Orthomyxoviridae Infections (epidemiology) |
| 1 | Orthomyxoviridae Infections (blood) |
| 1 | Orthomyxoviridae (pathogenicity) |
| 1 | Orthomyxoviridae (immunology) |
| 1 | Oregon |
| 1 | Nucleotide sequence |
| 1 | Nucleoproteins (classification) |
| 1 | Nose (virology) |
| 1 | Nose (immunology) |
| 1 | Nose (drug effects) |
| 1 | North America |
| 1 | North America (epidemiology) |
| 1 | New Zealand |
| 1 | New York |
| 1 | New York (epidemiology) |
| 1 | Neutrophil Infiltration |
| 1 | Neutralization Tests (veterinary) |
| 1 | Netherlands |
| 1 | N-Acetylneuraminic Acid (metabolism) |
| 1 | Myocardial Ischemia (mortality) |
| 1 | Mutation (genetics) |
| 1 | Mutant Proteins (genetics) |
| 1 | Mouse |
| 1 | Morbidity (trends) |
| 1 | Monoclonal antibody |
| 1 | Molecular Conformation |
| 1 | Models, Theoretical |
| 1 | Modeling |
| 1 | Mixed infection |
| 1 | Mink |
| 1 | Microbiological investigation |
| 1 | Microarray Analysis |
| 1 | Mice, Inbred CBA |
| 1 | Mice, Inbred C57BL |
| 1 | Method |
| 1 | Mass Vaccination (organization & administration) |
| 1 | Madin Darby Canine Kidney Cells |
| 1 | Lymphocytes (immunology) |
| 1 | Lymphocyte Activation |
| 1 | Lung (virology) |
| 1 | Lung (pathology) |
| 1 | Lung (drug effects) |
| 1 | Ligands |
| 1 | Killer Cells, Natural (immunology) |
| 1 | Japan |
| 1 | Italy (epidemiology) |
| 1 | Israel |
| 1 | Intestines (virology) |
| 1 | Interspecies transmission |
| 1 | Insecta |
| 1 | Influenzavirus A(H1N1) |
| 1 | Influenza, Human (pathology) |
| 1 | Influenza, Human (diagnosis) |
| 1 | Influenza, Human (blood) |
| 1 | Influenza viruses |
| 1 | Influenza virus |
| 1 | Influenza in Birds (pathology) |
| 1 | Influenza in Birds (metabolism) |
| 1 | Influenza in Birds (immunology) |
| 1 | Influenza in Birds (blood) |
| 1 | Influenza Vaccines |
| 1 | Influenza Vaccines (pharmacology) |
| 1 | Influenza Vaccines (genetics) |
| 1 | Influenza Vaccines (biosynthesis) |
| 1 | Influenza B virus (immunology) |
| 1 | Influenza A viruses |
| 1 | Influenza A virus (metabolism) |
| 1 | Influenza A virus (drug effects) |
| 1 | Influenza A virus (chemistry) |
| 1 | Influenza A Virus, H9N2 Subtype |
| 1 | Influenza A Virus, H9N2 Subtype (isolation & purification) |
| 1 | Influenza A Virus, H7N9 Subtype (metabolism) |
| 1 | Influenza A Virus, H7N9 Subtype (genetics) |
| 1 | Influenza A Virus, H7N9 Subtype (chemistry) |
| 1 | Influenza A Virus, H7N7 Subtype (isolation & purification) |
| 1 | Influenza A Virus, H7N7 Subtype (immunology) |
| 1 | Influenza A Virus, H5N1 Subtype |
| 1 | Influenza A Virus, H5N1 Subtype (pathogenicity) |
| 1 | Influenza A Virus, H5N1 Subtype (metabolism) |
| 1 | Influenza A Virus, H5N1 Subtype (isolation & purification) |
| 1 | Influenza A Virus, H5N1 Subtype (genetics) |
| 1 | Influenza A Virus, H3N2 Subtype (pathogenicity) |
| 1 | Influenza A Virus, H3N2 Subtype (metabolism) |
| 1 | Influenza A Virus, H3N2 Subtype (growth & development) |
| 1 | Influenza A Virus, H2N2 Subtype (metabolism) |
| 1 | Influenza A Virus, H2N2 Subtype (chemistry) |
| 1 | Influenza A Virus, H1N2 Subtype (pathogenicity) |
| 1 | Influenza A Virus, H1N2 Subtype (genetics) |
| 1 | Influenza A Virus, H1N1 Subtype (pathogenicity) |
| 1 | Influenza A Virus, H1N1 Subtype (isolation & purification) |
| 1 | Influenza A Virus, H1N1 Subtype (drug effects) |
| 1 | Influenza A Virus, H1N1 Subtype (chemistry) |
| 1 | Increase |
| 1 | Immunological method |
| 1 | Immunodiffusion |
| 1 | Immunization |
| 1 | Immunity, Maternally-Acquired |
| 1 | Immunity, Innate |
| 1 | IgG |
| 1 | Iceland |
| 1 | Iceland (epidemiology) |
| 1 | Humoral immunity |
| 1 | Host specificity |
| 1 | Host range |
| 1 | Host Specificity |
| 1 | Host Specificity (genetics) |
| 1 | Hospitalization (trends) |
| 1 | Horses |
| 1 | Horses (virology) |
| 1 | Horses (blood) |
| 1 | Horse Diseases (virology) |
| 1 | Horse Diseases (transmission) |
| 1 | Horse Diseases (epidemiology) |
| 1 | History, Ancient |
| 1 | History, 15th Century |
| 1 | Hemagglutinin Glycoproteins, Influenza Virus |
| 1 | Hemagglutinin Glycoproteins, Influenza Virus (history) |
| 1 | Hemagglutination |
| 1 | Hemagglutination inhibition test |
| 1 | Health Services Research |
| 1 | Health Maintenance Organizations |
| 1 | Health Care Rationing (methods) |
| 1 | HEK293 Cells |
| 1 | HA and NA |
| 1 | H9N2 |
| 1 | H3N2 |
| 1 | H2 subtype |
| 1 | H1N1 influenza pandemic |
| 1 | Guinea Pigs |
| 1 | Guanidines |
| 1 | Glycoproteins (chemistry) |
| 1 | Geography |
| 1 | Genetic variability |
| 1 | Genetic Variation |
| 1 | Genetic Complementation Test |
| 1 | Gene Expression |
| 1 | Fusion activity |
| 1 | Follow up study |
| 1 | Fab |
| 1 | F(ab′)2 |
| 1 | Europe (epidemiology) |
| 1 | Estimation |
| 1 | Epitopes |
| 1 | Epitopes, T-Lymphocyte (immunology) |
| 1 | Epitopes, T-Lymphocyte (chemistry) |
| 1 | Epidemiologic Methods |
| 1 | Enzyme Inhibitors (pharmacology) |
| 1 | Environmental epidemiology |
| 1 | Environmental Monitoring |
| 1 | England |
