| 2848 | Humans |
| 1727 | Influenza, Human (epidemiology) |
| 1106 | Influenza, Human (prevention & control) |
| 857 | Female |
| 729 | Male |
| 729 | Animals |
| 729 | Adult |
| 639 | Influenza, Human (virology) |
| 576 | Middle Aged |
| 533 | Pandemics |
| 513 | Adolescent |
| 486 | Disease Outbreaks (prevention & control) |
| 457 | Influenza A Virus, H1N1 Subtype |
| 447 | Disease Outbreaks |
| 447 | Child |
| 426 | Young Adult |
| 421 | Aged |
| 350 | Child, Preschool |
| 340 | History, 20th Century |
| 338 | Influenza Vaccines (immunology) |
| 308 | Influenza, Human (transmission) |
| 301 | Influenza Vaccines (administration & dosage) |
| 288 | Influenza A Virus, H1N1 Subtype (immunology) |
| 287 | Infant |
| 284 | Influenza, Human (mortality) |
| 270 | Influenza, Human (history) |
| 261 | Antiviral Agents (therapeutic use) |
| 245 | Influenza, Human (drug therapy) |
| 243 | Influenza A Virus, H1N1 Subtype (isolation & purification) |
| 236 | Pandemics (prevention & control) |
| 231 | United States (epidemiology) |
| 231 | Influenza, Human (immunology) |
| 193 | Influenza A Virus, H1N1 Subtype (genetics) |
| 187 | Aged, 80 and over |
| 180 | Influenza, Human (diagnosis) |
| 171 | Infant, Newborn |
| 163 | United States |
| 163 | Mice |
| 160 | Seasons |
| 156 | Risk Factors |
| 154 | Global Health |
| 144 | Influenza, Human (therapy) |
| 143 | Influenza, Human (complications) |
| 143 | Birds |
| 142 | Disease Outbreaks (history) |
| 141 | Time Factors |
| 138 | Influenza A Virus, H1N1 Subtype (pathogenicity) |
| 122 | Influenza A Virus, H5N1 Subtype (immunology) |
| 119 | Influenza A virus (genetics) |
| 113 | Surveys and Questionnaires |
| 113 | Antibodies, Viral (blood) |
| 112 | Vaccination |
| 111 | Orthomyxoviridae Infections (virology) |
| 109 | Pregnancy |
| 109 | Influenza Vaccines |
| 108 | Influenza A Virus, H5N1 Subtype |
| 106 | Influenza in Birds (epidemiology) |
| 106 | Hemagglutinin Glycoproteins, Influenza Virus (genetics) |
| 105 | Public Health |
| 105 | Influenza Vaccines (therapeutic use) |
| 105 | Disaster Planning (organization & administration) |
| 104 | Incidence |
| 103 | Mice, Inbred BALB C |
| 101 | Disaster Planning |
| 99 | Retrospective Studies |
| 98 | Influenza A Virus, H5N1 Subtype (pathogenicity) |
| 98 | Disease Outbreaks (statistics & numerical data) |
| 97 | Models, Theoretical |
| 96 | Pandemics (statistics & numerical data) |
| 96 | Cross-Sectional Studies |
| 95 | Influenza in Birds (virology) |
| 94 | Health Knowledge, Attitudes, Practice |
| 94 | Age Factors |
| 93 | Influenza Vaccines (supply & distribution) |
| 91 | World Health Organization |
| 91 | Models, Biological |
| 88 | Pandemics (history) |
| 88 | Influenza Vaccines (adverse effects) |
| 87 | Age Distribution |
| 86 | Hemagglutinin Glycoproteins, Influenza Virus (immunology) |
| 83 | Influenza in Birds (prevention & control) |
| 83 | Hospitalization (statistics & numerical data) |
| 82 | Orthomyxoviridae Infections (prevention & control) |
| 80 | Models, Statistical |
| 79 | Population Surveillance |
| 79 | Orthomyxoviridae Infections (immunology) |
| 79 | Molecular Sequence Data |
| 79 | Computer Simulation |
| 78 | Cell Line |
| 77 | Influenza A virus (pathogenicity) |
| 77 | Influenza A virus (immunology) |
| 77 | Attitude of Health Personnel |
| 74 | Influenza A Virus, H1N1 Subtype (physiology) |
| 73 | Vaccination (statistics & numerical data) |
| 73 | Phylogeny |
| 71 | Risk Assessment |
| 71 | Health Policy |
| 69 | Hemagglutination Inhibition Tests |
| 69 | Antibodies, Viral (immunology) |
| 67 | Influenza Pandemic, 1918-1919 (history) |
| 66 | Severity of Illness Index |
| 66 | Communicable Disease Control (methods) |
| 65 | Virulence |
| 65 | Influenza A Virus, H5N1 Subtype (genetics) |
| 65 | Antiviral Agents (pharmacology) |
| 64 | Swine |
| 64 | Influenza, Human (economics) |
| 63 | Influenza in Birds (transmission) |
| 62 | Population Surveillance (methods) |
| 61 | Oseltamivir (therapeutic use) |
| 60 | Disease Models, Animal |
| 59 | Treatment Outcome |
| 59 | Neuraminidase (genetics) |
| 59 | Neuraminidase (antagonists & inhibitors) |
| 59 | Influenza A Virus, H1N1 Subtype (drug effects) |
| 59 | China (epidemiology) |
| 58 | Influenza, Human (pathology) |
| 58 | Dogs |
| 57 | Australia (epidemiology) |
| 53 | Influenza Vaccines (genetics) |
| 53 | History, 21st Century |
| 53 | Drug Resistance, Viral |
| 53 | Cohort Studies |
| 53 | Antiviral Agents (administration & dosage) |
| 52 | Lung (virology) |
| 50 | Survival Analysis |
| 50 | Prospective Studies |
| 49 | Viral Proteins (genetics) |
| 49 | RNA, Viral (genetics) |
| 49 | Poultry |
| 49 | Europe (epidemiology) |
| 49 | Communicable Disease Control (organization & administration) |
| 47 | Prevalence |
| 47 | Mutation |
| 47 | Influenza A virus (classification) |
| 47 | Antiviral Agents (supply & distribution) |
| 46 | Virus Replication |
| 46 | Amino Acid Sequence |
| 45 | Vaccination (methods) |
| 45 | Antigens, Viral (immunology) |
| 44 | Sensitivity and Specificity |
| 44 | Hospitalization |
| 43 | United Kingdom (epidemiology) |
| 43 | Sentinel Surveillance |
| 43 | Reverse Transcriptase Polymerase Chain Reaction |
| 43 | Influenza, Human (psychology) |
| 42 | Influenza A virus |
| 42 | Influenza A virus (physiology) |
| 42 | Disaster Planning (methods) |
| 40 | Hemagglutinin Glycoproteins, Influenza Virus (metabolism) |
| 39 | Reassortant Viruses (genetics) |
| 39 | Neutralization Tests |
| 39 | Health Planning |
| 39 | Adjuvants, Immunologic (administration & dosage) |
| 38 | Socioeconomic Factors |
| 38 | Influenza Pandemic, 1918-1919 (mortality) |
| 38 | Hemagglutinin Glycoproteins, Influenza Virus (chemistry) |
| 37 | Influenza A virus (isolation & purification) |
| 37 | Infection Control (methods) |
| 37 | Hong Kong (epidemiology) |
| 37 | Ferrets |
| 36 | Orthomyxoviridae (immunology) |
| 36 | Lung (pathology) |
| 36 | Influenza A Virus, H1N1 Subtype (classification) |
| 36 | Evolution, Molecular |
| 36 | Absenteeism |
| 35 | Travel |
| 35 | Risk |
| 35 | Forecasting |
| 34 | Japan (epidemiology) |
| 34 | France (epidemiology) |
| 34 | Communication |
| 33 | Species Specificity |
| 33 | Pregnancy Complications, Infectious (prevention & control) |
| 33 | Data Collection |
| 33 | Cost-Benefit Analysis |
| 33 | Clinical Trials as Topic |
| 33 | Chickens |
| 32 | Vaccines, Inactivated (immunology) |
| 32 | Orthomyxoviridae Infections (veterinary) |
| 32 | Orthomyxoviridae Infections (epidemiology) |
| 32 | Mexico (epidemiology) |
| 32 | Influenza Vaccines (economics) |
| 32 | Influenza A Virus, H5N1 Subtype (isolation & purification) |
| 31 | Respiratory Tract Infections (epidemiology) |
| 31 | Health Personnel |
| 31 | England (epidemiology) |
| 31 | Communicable Disease Control |
| 30 | Vaccines, Synthetic (immunology) |
| 30 | Schools |
| 30 | Orthomyxoviridae Infections (pathology) |
| 30 | Influenza, Human (physiopathology) |
| 30 | Influenza Pandemic, 1918-1919 |
| 30 | Influenza A Virus, H3N2 Subtype (genetics) |
| 29 | Zoonoses (virology) |
| 29 | United Kingdom |
| 29 | Spain (epidemiology) |
| 29 | Practice Guidelines as Topic |
| 29 | Europe |
| 28 | Zoonoses (transmission) |
| 28 | World War I |
| 28 | Public Health Administration |
| 28 | Oseltamivir (pharmacology) |
| 28 | New Zealand (epidemiology) |
| 28 | Influenza A Virus, H3N2 Subtype (immunology) |
| 28 | Health Planning Guidelines |
| 28 | Health Care Surveys |
| 28 | Disease Transmission, Infectious (prevention & control) |
| 28 | China |
| 28 | Birds (virology) |
| 27 | Sequence Analysis, DNA |
| 27 | Models, Molecular |
| 27 | Mice, Inbred C57BL |
| 27 | Interviews as Topic |
| 27 | History, 19th Century |
| 27 | Germany (epidemiology) |
| 27 | Disease Outbreaks (economics) |
| 27 | Cross Reactions |
| 27 | Communicable Diseases (epidemiology) |
| 26 | Viral Load |
| 26 | Triage (methods) |
| 26 | Severe Acute Respiratory Syndrome (epidemiology) |
| 26 | Orthomyxoviridae Infections (transmission) |
| 26 | Orthomyxoviridae (pathogenicity) |
| 26 | Logistic Models |
| 26 | Algorithms |
| 25 | Swine Diseases (virology) |
| 25 | Public Health Practice |
| 25 | Madin Darby Canine Kidney Cells |
| 25 | Decision Making |
| 24 | Public Health (methods) |
| 24 | Orthomyxoviridae (genetics) |
| 24 | Military Personnel |
| 24 | Internet |
| 24 | Influenza, Human |
| 24 | Influenza in Birds (immunology) |
| 24 | Influenza A Virus, H5N1 Subtype (physiology) |
| 24 | Influenza A Virus, H3N2 Subtype (isolation & purification) |
| 24 | France |
| 24 | Comorbidity |
| 24 | Canada (epidemiology) |
| 24 | Base Sequence |
| 23 | Zoonoses (epidemiology) |
| 23 | Vaccines, Attenuated (immunology) |
| 23 | Vaccination (psychology) |
| 23 | Sex Factors |
| 23 | Respiratory Tract Infections (virology) |
| 23 | Qualitative Research |
| 23 | Pandemics (economics) |
| 23 | International Cooperation |
| 23 | Intensive Care Units |
| 23 | Influenza, Human (genetics) |
| 23 | Influenza, Human (blood) |
| 23 | Genome, Viral |
| 23 | Family Characteristics |
| 23 | Centers for Disease Control and Prevention, U.S. |
| 23 | Canada |
| 23 | Antiviral Agents (economics) |
| 22 | Receptors, Virus (metabolism) |
| 22 | Ontario (epidemiology) |
| 22 | Neuraminidase (metabolism) |
| 22 | Health Behavior |
| 22 | Geography |
| 22 | Genetic Variation |
| 22 | Cause of Death |
| 22 | Antiviral Agents (adverse effects) |
| 22 | Antigens, Viral (genetics) |
| 22 | Antibodies, Neutralizing (blood) |
| 21 | Real-Time Polymerase Chain Reaction |
| 21 | Patient Acceptance of Health Care (statistics & numerical data) |
| 21 | Influenza A Virus, H1N1 Subtype (growth & development) |
| 21 | Infection Control (organization & administration) |
| 21 | Health Services Accessibility |
| 21 | Databases, Factual |
| 21 | Cross Infection (prevention & control) |
| 21 | Cost of Illness |
| 20 | Workforce |
| 20 | Viral Proteins (metabolism) |
| 20 | Viral Matrix Proteins (immunology) |
| 20 | Sequence Alignment |
| 20 | Reproducibility of Results |
| 20 | Regression Analysis |
| 20 | Protein Binding |
| 20 | Orthomyxoviridae (isolation & purification) |
| 20 | Orthomyxoviridae (drug effects) |
| 20 | Odds Ratio |
| 20 | Netherlands (epidemiology) |
| 20 | Models, Economic |
| 20 | Mass Vaccination |
| 20 | Italy (epidemiology) |
| 20 | Influenza A Virus, H5N1 Subtype (drug effects) |
| 20 | India (epidemiology) |
| 20 | Health Planning (organization & administration) |
| 20 | Epidemics |
| 20 | Enzyme Inhibitors (therapeutic use) |
| 20 | Emergencies |
| 20 | Communicable Diseases, Emerging (epidemiology) |
| 20 | Communicable Disease Control (history) |
| 20 | Amino Acid Substitution |
| 19 | Zoonoses |
| 19 | Registries |
| 19 | Quarantine |
| 19 | Public Opinion |
| 19 | Protein Conformation |
| 19 | Pregnancy Complications, Infectious (epidemiology) |
| 19 | Poultry Diseases (virology) |
| 19 | Military Personnel (history) |
| 19 | Germany |
| 19 | Disease Reservoirs |
| 19 | Case-Control Studies |
| 19 | Anti-Bacterial Agents (therapeutic use) |
| 18 | Survival Rate |
| 18 | Seroepidemiologic Studies |
| 18 | Risk Assessment (methods) |
| 18 | Pilot Projects |
| 18 | Patient Acceptance of Health Care |
| 18 | Norway (epidemiology) |
| 18 | Neuraminidase (immunology) |
| 18 | Military Personnel (statistics & numerical data) |
| 18 | Immunization |
| 18 | Health Services Needs and Demand |
| 18 | Cross Protection |
| 18 | Communicable Diseases, Emerging (prevention & control) |
| 18 | Chick Embryo |
| 18 | Attitude to Health |
| 18 | Antiviral Agents (chemistry) |
| 17 | Vulnerable Populations |
| 17 | Viral Matrix Proteins (genetics) |
| 17 | Vaccines, DNA (immunology) |
| 17 | Taiwan (epidemiology) |
| 17 | Pneumonia, Viral (epidemiology) |
| 17 | Oseltamivir (administration & dosage) |
| 17 | Mass Casualty Incidents |
| 17 | Internationality |
| 17 | Influenza A virus (drug effects) |
| 17 | Influenza A Virus, H1N1 Subtype (metabolism) |
| 17 | Hospitals |
| 17 | Epidemiological Monitoring |
| 17 | Emergency Service, Hospital (statistics & numerical data) |
| 17 | Emergency Service, Hospital (organization & administration) |
| 17 | Developing Countries |
| 17 | Chlorocebus aethiops |
| 17 | CD8-Positive T-Lymphocytes (immunology) |
| 16 | Vaccines, Synthetic (genetics) |
| 16 | Urban Population |
| 16 | Swine (virology) |
| 16 | Sex Distribution |
| 16 | Reverse Transcriptase Polymerase Chain Reaction (methods) |
| 16 | Reassortant Viruses (pathogenicity) |
| 16 | Pneumonia, Viral (virology) |
| 16 | Neuraminidase (chemistry) |
| 16 | Influenza, Human (metabolism) |
| 16 | Influenza B virus (isolation & purification) |
| 16 | Health Personnel (psychology) |
| 16 | Follow-Up Studies |
| 16 | Drug Design |
| 16 | Disease Outbreaks (veterinary) |
| 16 | Disaster Planning (standards) |
| 16 | Australia |
| 16 | Antibodies, Neutralizing (immunology) |
| 16 | Adjuvants, Immunologic (pharmacology) |
| 15 | T-Lymphocytes (immunology) |
| 15 | Probability |
| 15 | Pregnancy Complications, Infectious (virology) |
| 15 | Polymerase Chain Reaction |
| 15 | Orthomyxoviridae (classification) |
| 15 | Mutation, Missense |
| 15 | Lung (immunology) |
| 15 | Intensive Care Units (statistics & numerical data) |
| 15 | Influenza, Human (ethnology) |
| 15 | Infection Control |
| 15 | Crystallography, X-Ray |
| 15 | Cluster Analysis |
| 15 | Brazil (epidemiology) |
| 15 | Basic Reproduction Number |
| 14 | Vero Cells |
| 14 | Vaccines, Synthetic (administration & dosage) |
| 14 | Universities |
| 14 | Schools (organization & administration) |
| 14 | Public Health (history) |
| 14 | Oseltamivir |
| 14 | Orthomyxoviridae Infections (mortality) |
| 14 | Occupational Health |
| 14 | Mortality |
| 14 | Mortality (trends) |
| 14 | Italy |
| 14 | Influenza Vaccines (standards) |
| 14 | Influenza A virus (metabolism) |
| 14 | Host-Pathogen Interactions |
| 14 | Hemagglutinins, Viral (genetics) |
| 14 | Health Planning (methods) |
| 14 | Enzyme Inhibitors (pharmacology) |
| 14 | Confidence Intervals |
| 14 | Cells, Cultured |
| 14 | CD4-Positive T-Lymphocytes (immunology) |
| 14 | Asia (epidemiology) |
| 14 | Antibodies, Viral (biosynthesis) |
| 14 | Acetamides (therapeutic use) |
| 13 | Swine Diseases (epidemiology) |
| 13 | Squalene (administration & dosage) |
| 13 | Singapore (epidemiology) |
| 13 | Severe Acute Respiratory Syndrome (prevention & control) |
| 13 | Respiratory Distress Syndrome, Adult (therapy) |
| 13 | Reassortant Viruses (immunology) |
| 13 | Protein Structure, Tertiary |
| 13 | Poultry (virology) |
| 13 | Pneumonia, Bacterial (mortality) |
| 13 | Patient Isolation |
| 13 | Oseltamivir (adverse effects) |
| 13 | Needs Assessment |
| 13 | Nasopharynx (virology) |
| 13 | Multivariate Analysis |
| 13 | Moral Obligations |
| 13 | Models, Immunological |
| 13 | Mass Media |
| 13 | Japan |
| 13 | Influenza, Human (microbiology) |
| 13 | Influenza Vaccines (pharmacology) |
| 13 | Influenza Vaccines (chemistry) |
| 13 | Influenza A Virus, H7N9 Subtype (immunology) |
| 13 | Influenza A Virus, H3N2 Subtype |
| 13 | Influenza A Virus, H1N1 Subtype (enzymology) |
| 13 | Infectious Disease Transmission, Patient-to-Professional (prevention & control) |
| 13 | Immunization Programs |
| 13 | Hygiene |
| 13 | Hemagglutinins, Viral (immunology) |
| 13 | Health Care Rationing (ethics) |
| 13 | Guidelines as Topic |
| 13 | Genotype |
| 13 | Gene Expression Profiling |
| 13 | Focus Groups |
| 13 | Enzyme-Linked Immunosorbent Assay |
| 13 | Disease Outbreaks (ethics) |
| 13 | Community-Acquired Infections (epidemiology) |
| 13 | Coinfection (virology) |
| 13 | Coinfection (epidemiology) |
| 13 | Biological Evolution |
| 13 | Binding Sites |
| 13 | Asia |
| 13 | Administration, Intranasal |
| 13 | Adjuvants, Immunologic |
| 12 | Virus Shedding |
| 12 | Virus Replication (drug effects) |
| 12 | Vaccines, Inactivated (administration & dosage) |
| 12 | Thailand (epidemiology) |
| 12 | Technology, Pharmaceutical (methods) |
| 12 | Stochastic Processes |
| 12 | Spain |
| 12 | Social Justice |
| 12 | Respiratory System (virology) |
| 12 | Quality-Adjusted Life Years |
| 12 | Program Evaluation |
| 12 | Poultry Diseases (epidemiology) |
| 12 | Polysorbates (administration & dosage) |
| 12 | Physician's Role |
| 12 | Monte Carlo Method |
| 12 | Mexico |
| 12 | Masks |
| 12 | Intensive Care Units (organization & administration) |
| 12 | Information Dissemination |
| 12 | Influenza, Human (etiology) |
| 12 | Influenza B virus (genetics) |
| 12 | Immunoglobulin G (blood) |
| 12 | Immunization Schedule |
| 12 | Immunity, Cellular |
| 12 | Health Surveys |
| 12 | Hand Disinfection |
| 12 | Genetic Vectors |
| 12 | Genetic Drift |
| 12 | Genes, Viral |
| 12 | Ferrets (virology) |
| 12 | European Union |
| 12 | Ethics, Medical |
| 12 | Epidemics (prevention & control) |
| 12 | Dose-Response Relationship, Immunologic |
| 12 | Dose-Response Relationship, Drug |
| 12 | Disease Transmission, Infectious |
| 12 | Cross Reactions (immunology) |
| 12 | Cooperative Behavior |
| 11 | Virus Attachment |
| 11 | Viral Proteins (antagonists & inhibitors) |
| 11 | Vaccines, DNA (administration & dosage) |
| 11 | Urban Population (statistics & numerical data) |
| 11 | Trust |
| 11 | Travel (statistics & numerical data) |
| 11 | Sweden (epidemiology) |
| 11 | Spatio-Temporal Analysis |
| 11 | Recombination, Genetic |
| 11 | RNA Replicase (genetics) |
| 11 | Public Policy |
| 11 | Prognosis |
| 11 | Predictive Value of Tests |
| 11 | Pneumonia, Bacterial (etiology) |
| 11 | Ontario |
| 11 | New Zealand |
| 11 | Mass Vaccination (methods) |
| 11 | Longitudinal Studies |
| 11 | Influenza, Human (nursing) |
| 11 | Influenza Vaccines (isolation & purification) |
| 11 | Influenza Vaccines (history) |
