| 88 | Humans |
| 58 | Animals |
| 39 | Influenza, Human (virology) |
| 39 | Influenza, Human (epidemiology) |
| 23 | Influenza A virus (immunology) |
| 21 | Influenza A virus (genetics) |
| 19 | Disease Outbreaks |
| 18 | Influenza, Human (immunology) |
| 18 | Female |
| 17 | Molecular Sequence Data |
| 17 | Influenza A Virus, H2N2 Subtype (immunology) |
| 17 | Adult |
| 16 | Middle Aged |
| 16 | Influenza, Human (transmission) |
| 16 | Influenza A Virus, H2N2 Subtype (genetics) |
| 15 | History, 20th Century |
| 14 | Influenza, Human (history) |
| 14 | Adolescent |
| 13 | Pandemics |
| 13 | Mice |
| 13 | Influenza A Virus, H2N2 Subtype |
| 13 | Child |
| 13 | Child, Preschool |
| 12 | Influenza, Human (prevention & control) |
| 12 | Human |
| 12 | Birds |
| 12 | Amino Acid Sequence |
| 11 | Phylogeny |
| 11 | Influenza in Birds (virology) |
| 11 | Hemagglutinin Glycoproteins, Influenza Virus (genetics) |
| 11 | Hemagglutination Inhibition Tests |
| 11 | Antibodies, Viral (immunology) |
| 10 | Models, Molecular |
| 10 | Influenza |
| 10 | Infant |
| 10 | Aged |
| 9 | Viral Proteins (genetics) |
| 9 | Neuraminidase (genetics) |
| 9 | Male |
| 9 | Influenza Vaccines (immunology) |
| 9 | Influenza A virus |
| 9 | Influenza A Virus, H1N1 Subtype (immunology) |
| 9 | Hemagglutinin Glycoproteins, Influenza Virus (immunology) |
| 9 | Epidemiology |
| 9 | Cross Reactions |
| 8 | Young Adult |
| 8 | Reassortant Viruses (genetics) |
| 8 | Mutation |
| 8 | Influenza in Birds (epidemiology) |
| 8 | Influenza A Virus, H3N2 Subtype |
| 8 | Influenza A Virus, H2N2 Subtype (isolation & purification) |
| 8 | Hemagglutinin Glycoproteins, Influenza Virus (chemistry) |
| 7 | Swine |
| 7 | Orthomyxoviridae Infections (immunology) |
| 7 | Neuraminidase (immunology) |
| 7 | Influenza, Human (mortality) |
| 7 | Influenza A |
| 7 | Influenza A virus (pathogenicity) |
| 7 | Influenza A virus (isolation & purification) |
| 7 | Influenza A Virus, H1N1 Subtype (genetics) |
| 7 | Hemagglutinin Glycoproteins, Influenza Virus (metabolism) |
| 7 | Ferrets |
| 7 | Evolution, Molecular |
| 7 | Antibodies, Viral (blood) |
| 6 | Species Specificity |
| 6 | Sequence Analysis, DNA |
| 6 | Sequence Alignment |
| 6 | Orthomyxoviridae Infections (virology) |
| 6 | Orthomyxoviridae Infections (prevention & control) |
| 6 | Neuraminidase (metabolism) |
| 6 | Models, Biological |
| 6 | Mice, Inbred BALB C |
| 6 | Influenza A virus (physiology) |
| 6 | Influenza A virus (enzymology) |
| 6 | Influenza A virus (classification) |
| 6 | Influenza A Virus, H3N2 Subtype (genetics) |
| 6 | Influenza A Virus, H2N2 Subtype (pathogenicity) |
| 6 | Influenza A Virus, H1N1 Subtype |
| 6 | Infant, Newborn |
| 6 | Hemagglutinins, Viral (analysis) |
| 6 | Hemagglutinin |
| 6 | Base Sequence |
| 6 | Antibodies, Viral (analysis) |
| 5 | Receptors, Virus (metabolism) |
| 5 | Influenzavirus A |
| 5 | Influenza, Human (genetics) |
| 5 | Influenza Vaccines (administration & dosage) |
| 5 | Dogs |
| 5 | Disease Outbreaks (history) |
| 5 | Chick Embryo |
| 5 | Cell Line |
| 5 | Binding Sites |
| 5 | Antiviral Agents (therapeutic use) |
| 5 | Antibodies, Neutralizing (immunology) |
| 5 | Antibodies, Monoclonal (immunology) |
| 4 | Zoonoses (virology) |
| 4 | Zoonoses (epidemiology) |
| 4 | Virus Replication |
| 4 | Vaccines, Inactivated (immunology) |
| 4 | United States (epidemiology) |
| 4 | Time Factors |
| 4 | Seasons |
| 4 | Recombination, Genetic |
| 4 | Reassortant Viruses (immunology) |
| 4 | RNA, Viral (genetics) |
| 4 | Neutralization Tests |
| 4 | Neuraminidase (antagonists & inhibitors) |
| 4 | Influenza, Human (blood) |
| 4 | Influenza in Birds (transmission) |
| 4 | Influenza A Virus, H5N1 Subtype (immunology) |
| 4 | Influenza A Virus, H5N1 Subtype (genetics) |
| 4 | Influenza A Virus, H3N2 Subtype (immunology) |
| 4 | Influenza A Virus, H2N2 Subtype (chemistry) |
| 4 | Epidemic |
| 4 | Cross Reactions (immunology) |
| 4 | Aves |
| 4 | Antigens, Viral (analysis) |
| 3 | Virulence |
| 3 | Viral Proteins (metabolism) |
| 3 | Viral Proteins (immunology) |
| 3 | Vaccines, Attenuated (immunology) |
| 3 | Transmission from animal to man |
| 3 | Swine (virology) |
| 3 | Survival Analysis |
| 3 | Subtype |
| 3 | Stochastic Processes |
| 3 | Russia |
| 3 | Risk Assessment |
| 3 | Protein Conformation |
| 3 | Population Surveillance |
| 3 | Pandemics (prevention & control) |
| 3 | Pandemics (history) |
| 3 | Orthomyxoviridae (immunology) |
| 3 | Origin |
| 3 | Neuraminidase (chemistry) |
| 3 | Mutation, Missense |
| 3 | Microbiology |
| 3 | Lung (immunology) |
| 3 | Influenzavirus |
| 3 | Influenza, Human (pathology) |
| 3 | Influenza Vaccines |
| 3 | Influenza A virus (growth & development) |
| 3 | Influenza A virus (drug effects) |
| 3 | Influenza A Virus, H3N2 Subtype (chemistry) |
| 3 | Influenza A Virus, H2N2 Subtype (metabolism) |
| 3 | Immunity, Humoral |
| 3 | Immune response |
| 3 | Hydrogen-Ion Concentration |
| 3 | Hong Kong (epidemiology) |
| 3 | Hemagglutinins, Viral (immunology) |
| 3 | Genes, Viral |
| 3 | Exo-α-sialidase |
| 3 | Epitopes (analysis) |
| 3 | Disease Outbreaks (prevention & control) |
| 3 | Disease Models, Animal |
| 3 | Crystallography, X-Ray |
| 3 | Computer Simulation |
| 3 | Cells, Cultured |
| 3 | Case history |
| 3 | Biological Evolution |
| 3 | Asia (epidemiology) |
| 3 | Antiviral Agents (pharmacology) |
| 3 | Antigens, Viral (immunology) |
| 3 | Antibodies, Neutralizing (blood) |
| 3 | Amino Acid Substitution |
| 3 | Algorithms |
| 3 | Aged, 80 and over |
| 3 | Age Distribution |
| 2 | Zoonoses (transmission) |
| 2 | Viral Proteins (chemistry) |
| 2 | Vaccines, Synthetic (immunology) |
| 2 | Vaccines, Attenuated (genetics) |
| 2 | Vaccination |
| 2 | United States |
| 2 | Temperature |
| 2 | T-Lymphocytes (immunology) |
| 2 | Swine Diseases (virology) |
| 2 | Strain |
| 2 | Spain (epidemiology) |
| 2 | Sequence Homology, Amino Acid |
| 2 | Sensitivity and Specificity |
| 2 | Reverse Genetics |
| 2 | Reproducibility of Results |
| 2 | Replication |
| 2 | Receptors, Virus (genetics) |
| 2 | Receptors, Virus (chemistry) |
| 2 | Rabbits |
| 2 | Protein Binding |
| 2 | Prevalence |
| 2 | Poultry |
| 2 | Polysaccharides (metabolism) |
| 2 | Phenotype |
| 2 | Peptides (analysis) |
| 2 | Pandemic |
| 2 | Orthomyxoviridae Infections (veterinary) |
| 2 | Orthomyxoviridae (genetics) |
| 2 | North America |
| 2 | N-Acetylneuraminic Acid (metabolism) |
| 2 | Mutagenesis, Site-Directed |
| 2 | Monoclonal antibody |
| 2 | Molecular evolution |
| 2 | Molecular epidemiology |
| 2 | Models, Theoretical |
| 2 | Models, Genetic |
| 2 | Mammalia |
| 2 | Madin Darby Canine Kidney Cells |
| 2 | Lung (virology) |
| 2 | Lung (pathology) |
| 2 | Japan |
| 2 | Influenza, Human (microbiology) |
| 2 | Influenza, Human (drug therapy) |
| 2 | Influenza in Birds (history) |
| 2 | Influenza in Birds (genetics) |
| 2 | Influenza Vaccines (pharmacology) |
| 2 | Influenza Vaccines (genetics) |
| 2 | Influenza B virus |
| 2 | Influenza B virus (immunology) |
| 2 | Influenza A virus (chemistry) |
| 2 | Influenza A Virus, H7N7 Subtype (immunology) |
| 2 | Influenza A Virus, H5N1 Subtype (isolation & purification) |
| 2 | Influenza A Virus, H3N2 Subtype (metabolism) |
| 2 | Influenza A Virus, H2N2 Subtype (physiology) |
| 2 | Influenza A Virus, H2N2 Subtype (growth & development) |
| 2 | Influenza A Virus, H1N1 Subtype (drug effects) |
| 2 | Influenza A Virus, H1N1 Subtype (chemistry) |
| 2 | Infection |
| 2 | Immunity |
| 2 | Immune Sera (immunology) |
| 2 | Hong Kong |
| 2 | History, Medieval |
| 2 | History, 19th Century |
| 2 | History, 18th Century |
| 2 | History, 17th Century |
| 2 | History, 16th Century |
| 2 | Hemagglutinins, Viral (genetics) |
| 2 | Hemagglutinin Glycoproteins, Influenza Virus |
| 2 | HeLa Cells |
| 2 | Global Health |
| 2 | Genetic reassortment |
| 2 | Genetic Variation |
| 2 | Genetic Complementation Test |
| 2 | Genes, Viral (genetics) |
| 2 | Gene |
| 2 | Epitopes |
| 2 | Epitopes, T-Lymphocyte (immunology) |
| 2 | Epitopes (immunology) |
| 2 | Epitopes (chemistry) |
| 2 | Enzyme Stability |
| 2 | Enzyme Inhibitors (pharmacology) |
| 2 | Ducks |
| 2 | Ducks (virology) |
| 2 | Ducks (microbiology) |
| 2 | Disaster Planning |
| 2 | Cross Protection |
| 2 | Computational Biology |
| 2 | Cluster Analysis |
| 2 | Chlorocebus aethiops |
| 2 | Birds (virology) |
| 2 | Bioterrorism |
| 2 | Biological receptor |
| 2 | B-Lymphocytes (immunology) |
| 2 | Avian influenzavirus |
| 2 | Avian influenza |
| 2 | Asia |
| 2 | Antiviral Agents (chemistry) |
| 2 | Antigens, Viral (genetics) |
| 2 | Antibodies, Viral (genetics) |
| 2 | Antibodies, Neutralizing (chemistry) |
| 2 | Antibodies, Monoclonal |
| 2 | Amino Acids (analysis) |
| 2 | Age |
| 2 | Age Factors |
| 2 | Adsorption |
| 1 | schizophrenia |
| 1 | retrograde rays |
| 1 | prenatal influenza |
| 1 | phylogenetic analysis |
| 1 | neurodevelopment |
| 1 | migratory duck |
| 1 | influenza virus |
| 1 | etiology |
| 1 | epidemiology |
| 1 | canal rays |
| 1 | Zoonoses |
| 1 | Zoonoses (history) |
| 1 | Zanamivir |
| 1 | Zanamivir (pharmacology) |
| 1 | Zanamivir (chemistry) |
| 1 | Zanamivir (analogs & derivatives) |
| 1 | Young adult |
| 1 | World Health Organization |
| 1 | Woldemar Voigt |
| 1 | Viruses (isolation & purification) |
| 1 | Viruses (classification) |
| 1 | Virus replication cycle |
| 1 | Virus Shedding |
| 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 Cultivation |
| 1 | Virus Cultivation (methods) |
| 1 | Virulence (genetics) |
| 1 | Virology |
| 1 | Virion (metabolism) |
| 1 | Virion (genetics) |
| 1 | Virion (chemistry) |
| 1 | Viral disease |
| 1 | Viral Structural Proteins (genetics) |
| 1 | Viral Proteins (physiology) |
| 1 | Viral Proteins (antagonists & inhibitors) |
| 1 | Viral Proteins (analysis) |
| 1 | Viral Nonstructural Proteins (genetics) |
| 1 | Viral Matrix Proteins |
| 1 | Vietnam |
| 1 | Vero Cells |
| 1 | Vaccines, Synthetic (genetics) |
| 1 | Vaccines, Synthetic (administration & dosage) |
| 1 | Vaccines, Inactivated (pharmacology) |
| 1 | Vaccines, Inactivated (isolation & purification) |
| 1 | Vaccines, Inactivated (administration & dosage) |
| 1 | Vaccines, DNA (immunology) |
| 1 | Vaccines, Attenuated |
| 1 | Vaccines, Attenuated (administration & dosage) |
| 1 | Vaccine tablet |
| 1 | Vaccination (methods) |
| 1 | Vaccination (history) |
| 1 | Up-Regulation |
| 1 | United Kingdom (epidemiology) |
| 1 | Tyrosine (metabolism) |
| 1 | Tumor Cells, Cultured |
| 1 | Tryptophan (metabolism) |
| 1 | Tryptophan (immunology) |
| 1 | Tropical medicine |
| 1 | Tropical Climate |
| 1 | Transmission |
| 1 | Transmission from animal to animal |
| 1 | Transfection |
| 1 | Thiophosphinyl guanidine |
| 1 | Tanzania |
| 1 | Taiwan (epidemiology) |
| 1 | Tablets |
| 1 | T-Lymphocytes, Cytotoxic (immunology) |
| 1 | Swine Diseases (transmission) |
| 1 | Swine Diseases (epidemiology) |
| 1 | Swine (blood) |
| 1 | Sus scrofa (virology) |
| 1 | Survival |
| 1 | Survival Rate |
| 1 | Substrate Specificity |
| 1 | Structure-Activity Relationship |
| 1 | Stark-Lo Surdo phenomenon |
| 1 | Stark effect |
| 1 | Species specificity |
| 1 | Software |
| 1 | Sialic Acids (pharmacology) |
| 1 | Sialic Acids (metabolism) |
| 1 | Serotyping |
| 1 | Serologic Tests |
| 1 | Seroepidemiologic Studies |
| 1 | Sequence alignment |
| 1 | Sequence Homology, Nucleic Acid |
| 1 | Sentinel Surveillance |
| 1 | Sensitivity |
| 1 | Selection, Genetic |
| 1 | Selection Bias |
| 1 | Seals, Earless |
| 1 | Seals, Earless (virology) |
| 1 | Risk Factors |
| 1 | Ribavirin (pharmacology) |
| 1 | Review |
| 1 | Reversion |
| 1 | Reverse Transcriptase Polymerase Chain Reaction |
| 1 | Reverse Transcriptase Polymerase Chain Reaction (methods) |
| 1 | Respiratory system |
| 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 | Respiration |
| 1 | Residence Characteristics |
| 1 | Reservoir |
| 1 | Research |
| 1 | Recurrence |
| 1 | Recombinant Fusion Proteins (metabolism) |
| 1 | Receptors, Virus (physiology) |
| 1 | Receptors, IgG (immunology) |
| 1 | Receptors, IgG (genetics) |
| 1 | Receptors, IgG (deficiency) |
| 1 | Receptors, Cell Surface (metabolism) |
| 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 | Radioimmunoassay (methods) |
| 1 | RNA, Messenger (genetics) |
| 1 | RNA Replicase (genetics) |
| 1 | Pyrans |
| 1 | Public Opinion (history) |
| 1 | Public Health |
| 1 | Protein Structure, Secondary |
| 1 | Protease Inhibitors (pharmacology) |
| 1 | Protease Inhibitors (isolation & purification) |
| 1 | Protease Inhibitors (chemistry) |
| 1 | Property structure relationship |
| 1 | Propagation velocity |
| 1 | Prodrugs (pharmacology) |
| 1 | Prodrugs (chemistry) |
| 1 | Primary structure |
| 1 | Predictive Value of Tests |
| 1 | Pre-clinical evaluation |
| 1 | Poultry Diseases (virology) |
| 1 | Poultry Diseases (metabolism) |
| 1 | Poultry Diseases (genetics) |
| 1 | Poultry (virology) |
| 1 | Polysaccharides (chemistry) |
| 1 | Polymorphism, Single-Stranded Conformational |
| 1 | Pneumonia |
| 1 | Plant Stems (chemistry) |
| 1 | Plant Bark (chemistry) |
| 1 | Plague (transmission) |
| 1 | Plague (history) |
| 1 | Plague (epidemiology) |
| 1 | Pig |
| 1 | Phylogenetic tree |
| 1 | Phosphinyl guanidine |
| 1 | Perspective |
| 1 | Pathogenesis |
| 1 | Passive immunity |
| 1 | Parvovirus, Canine (physiology) |
| 1 | Parvovirus, Canine (pathogenicity) |
| 1 | Parvovirus, Canine (genetics) |
| 1 | Parvovirus, Canine (chemistry) |
| 1 | Oxidative stress |
| 1 | Oseltamivir (pharmacology) |
| 1 | Oseltamivir (chemistry) |
| 1 | Orthomyxoviridae Infections |
| 1 | Orthomyxoviridae Infections (pathology) |
| 1 | Orthomyxoviridae Infections (mortality) |
| 1 | Orthomyxoviridae Infections (history) |
| 1 | Orthomyxoviridae Infections (genetics) |
| 1 | Orthomyxoviridae Infections (epidemiology) |
| 1 | Orthomyxoviridae Infections (drug therapy) |
| 1 | Orthomyxoviridae Infections (blood) |
| 1 | Orthomyxoviridae (pathogenicity) |
| 1 | Ohio (epidemiology) |
| 1 | Nucleoproteins (genetics) |
| 1 | Nucleic Acid Hybridization |
| 1 | Nose (virology) |
| 1 | Nose (immunology) |
| 1 | Nose (drug effects) |
| 1 | Newspapers as Topic |
| 1 | New Zealand |
| 1 | New York |
| 1 | New York (epidemiology) |
| 1 | Neutrophil Infiltration |
| 1 | Neutralization Tests (veterinary) |
| 1 | Neutralization Tests (standards) |
| 1 | Neuraminidase |
| 1 | Neuraminidase (isolation & purification) |
| 1 | Neuraminidase (analysis) |
| 1 | Netherlands |
| 1 | Netherlands (epidemiology) |
| 1 | N-Acetylneuraminic Acid (genetics) |
| 1 | Mycoplasma |
| 1 | Mutation (genetics) |
| 1 | Mucosal vaccination |
| 1 | Mouth Mucosa |
| 1 | Mouse |
| 1 | Mortality |
| 1 | Morbidity (trends) |
| 1 | Molecular Structure |
| 1 | Mixed infection |
| 1 | Mink |
| 1 | Military Personnel |
| 1 | Microbial Sensitivity Tests |
| 1 | Microarray Analysis |
| 1 | Mice, Inbred DBA |
| 1 | Mice, Inbred CBA |
| 1 | Mice, Inbred C57BL |
| 1 | Mexico (epidemiology) |
| 1 | Method |
| 1 | Medical Records |
| 1 | Mechanism of action |
| 1 | Mathematical Concepts |
| 1 | Mass Vaccination (organization & administration) |
| 1 | Mangifera (chemistry) |
| 1 | Lymphocytes (immunology) |
| 1 | Lymphocyte Activation |
| 1 | Lung (drug effects) |
| 1 | Lo Surdo method |
| 1 | Ligands |
| 1 | Leukocytes, Mononuclear (immunology) |
| 1 | Killer Cells, Natural (immunology) |
