| 109 | Humans |
| 69 | Belgium (epidemiology) |
| 67 | Male |
| 66 | Female |
| 60 | Belgium |
| 48 | Adult |
| 47 | Middle Aged |
| 46 | Aged |
| 44 | Influenza, Human (epidemiology) |
| 33 | Influenza, Human (prevention & control) |
| 28 | Animals |
| 25 | Adolescent |
| 24 | Young Adult |
| 23 | Aged, 80 and over |
| 21 | Child |
| 20 | Influenza Vaccines (administration & dosage) |
| 20 | Child, Preschool |
| 16 | Infant |
| 14 | Surveys and Questionnaires |
| 14 | Influenza, Human (virology) |
| 14 | Influenza, Human (diagnosis) |
| 13 | Seasons |
| 13 | Influenza in Birds (epidemiology) |
| 13 | Influenza A virus (isolation & purification) |
| 11 | Risk Factors |
| 11 | Retrospective Studies |
| 11 | Cross-Sectional Studies |
| 9 | Vaccination (statistics & numerical data) |
| 9 | Sensitivity and Specificity |
| 9 | Prevalence |
| 9 | Infant, Newborn |
| 9 | Incidence |
| 8 | Vaccination |
| 8 | Time Factors |
| 8 | Influenza Vaccines |
| 8 | Influenza A virus (immunology) |
| 8 | Influenza A Virus, H1N1 Subtype |
| 7 | Sentinel Surveillance |
| 7 | Prospective Studies |
| 7 | Influenza in Birds (virology) |
| 7 | Disease Outbreaks |
| 7 | Disease Outbreaks (statistics & numerical data) |
| 7 | Disease Outbreaks (prevention & control) |
| 7 | Antibodies, Viral (blood) |
| 6 | Swine |
| 6 | Seroepidemiologic Studies |
| 6 | Pregnancy |
| 6 | Population Surveillance (methods) |
| 6 | Orthomyxoviridae Infections (veterinary) |
| 6 | Orthomyxoviridae Infections (epidemiology) |
| 6 | Netherlands (epidemiology) |
| 6 | Logistic Models |
| 6 | Influenza, Human (immunology) |
| 6 | Influenza Vaccines (adverse effects) |
| 6 | Disease Outbreaks (veterinary) |
| 6 | Antiviral Agents (therapeutic use) |
| 6 | Age Factors |
| 5 | Virus Diseases (epidemiology) |
| 5 | Socioeconomic Factors |
| 5 | Respiratory Tract Infections (epidemiology) |
| 5 | Poultry |
| 5 | Pandemics |
| 5 | Orthomyxoviridae (isolation & purification) |
| 5 | Netherlands |
| 5 | Influenza, Human (drug therapy) |
| 5 | Influenza Vaccines (immunology) |
| 5 | Health Knowledge, Attitudes, Practice |
| 5 | Cohort Studies |
| 5 | Attitude of Health Personnel |
| 4 | Risk Assessment |
| 4 | Regression Analysis |
| 4 | Population Surveillance |
| 4 | Phylogeny |
| 4 | Patient Acceptance of Health Care |
| 4 | Multivariate Analysis |
| 4 | Influenza, Human (therapy) |
| 4 | Influenza, Human (mortality) |
| 4 | Influenza, Human (economics) |
| 4 | Influenza Vaccines (therapeutic use) |
| 4 | Influenza A Virus, H5N1 Subtype |
| 4 | Influenza A Virus, H1N1 Subtype (immunology) |
| 4 | Hemagglutination Inhibition Tests |
| 4 | Germany (epidemiology) |
| 4 | France (epidemiology) |
| 4 | Europe (epidemiology) |
| 4 | Epidemiological Monitoring |
| 4 | Enzyme-Linked Immunosorbent Assay (veterinary) |
| 4 | Diagnosis, Differential |
| 4 | Birds |
| 4 | Antibodies, Viral (analysis) |
| 4 | Age Distribution |
| 3 | Virus Diseases (virology) |
| 3 | Vaccination (psychology) |
| 3 | Vaccination (economics) |
| 3 | Travel |
| 3 | Switzerland (epidemiology) |
| 3 | Swine Diseases (virology) |
| 3 | Swine Diseases (epidemiology) |
| 3 | Statistics, Nonparametric |
| 3 | Respiratory Tract Infections (virology) |
| 3 | Respiratory Tract Diseases (epidemiology) |
| 3 | Respiratory Syncytial Viruses (isolation & purification) |
| 3 | Pregnancy Complications, Infectious (prevention & control) |
| 3 | Pneumococcal Vaccines |
| 3 | Oseltamivir (therapeutic use) |
| 3 | Orthomyxoviridae Infections (virology) |
| 3 | Odds Ratio |
| 3 | Nursing Homes |
| 3 | Nasopharynx (virology) |
| 3 | Models, Theoretical |
| 3 | Models, Statistical |
| 3 | Internet |
| 3 | Intensive Care Units (statistics & numerical data) |
| 3 | Influenza, Human (transmission) |
| 3 | Influenza, Human (psychology) |
| 3 | Influenza, Human (complications) |
| 3 | Influenza in Birds (prevention & control) |
| 3 | Influenza B virus (isolation & purification) |
| 3 | Influenza B virus (immunology) |
| 3 | Influenza A virus (genetics) |
| 3 | Influenza A Virus, H5N1 Subtype (pathogenicity) |
| 3 | Influenza A Virus, H5N1 Subtype (isolation & purification) |
| 3 | Influenza A Virus, H5N1 Subtype (genetics) |
| 3 | Influenza A Virus, H1N1 Subtype (isolation & purification) |
| 3 | Influenza A Virus, H1N1 Subtype (genetics) |
| 3 | Immunization Schedule |
| 3 | Hospitals |
| 3 | Hospitalization |
| 3 | Health Surveys |
| 3 | Genetic Variation |
| 3 | Educational Status |
| 3 | Drug-Related Side Effects and Adverse Reactions (pathology) |
| 3 | Drug-Related Side Effects and Adverse Reactions (epidemiology) |
| 3 | Denmark (epidemiology) |
| 3 | Data Collection |
| 3 | Communicable Disease Control (methods) |
| 3 | Chi-Square Distribution |
| 3 | Antibodies, Bacterial (blood) |
| 2 | alpha-Tocopherol (administration & dosage) |
| 2 | Whooping Cough (prevention & control) |
| 2 | Virulence |
| 2 | Virology (methods) |
| 2 | Vaccines, Inactivated |
| 2 | Vaccination Coverage (statistics & numerical data) |
| 2 | Vaccination (methods) |
| 2 | United Kingdom (epidemiology) |
| 2 | Treatment Outcome |
| 2 | Tetanus Toxoid (immunology) |
| 2 | Tetanus Toxoid (adverse effects) |
| 2 | Tetanus Toxoid (administration & dosage) |
| 2 | Survival Analysis |
| 2 | Students, Medical |
| 2 | Streptococcus pneumoniae (isolation & purification) |
| 2 | Squalene (administration & dosage) |
| 2 | Social Behavior |
| 2 | Smoking Prevention |
| 2 | Smoking (legislation & jurisprudence) |
| 2 | Serotyping |
| 2 | Risk |
| 2 | Risk Assessment (methods) |
| 2 | Renal Dialysis |
| 2 | Real-Time Polymerase Chain Reaction |
| 2 | Random Allocation |
| 2 | RNA, Viral (genetics) |
| 2 | Public Health |
| 2 | Pseudorabies (epidemiology) |
| 2 | Probability |
| 2 | Primary Health Care (methods) |
| 2 | Preventive Health Services (statistics & numerical data) |
| 2 | Pregnant Women |
| 2 | Predictive Value of Tests |
| 2 | Practice Patterns, Physicians' |
| 2 | Practice Guidelines as Topic |
| 2 | Poultry Diseases (virology) |
| 2 | Poultry Diseases (epidemiology) |
| 2 | Portugal (epidemiology) |
| 2 | Population Control (methods) |
| 2 | Polysorbates (administration & dosage) |
| 2 | Polymerase Chain Reaction |
| 2 | Pilot Projects |
| 2 | Physicians, Family |
| 2 | Pharmacies |
| 2 | Patient Admission (statistics & numerical data) |
| 2 | Patient Acceptance of Health Care (statistics & numerical data) |
| 2 | Nasal Mucosa (virology) |
| 2 | Molecular Sequence Data |
| 2 | Molecular Epidemiology (methods) |
| 2 | Molecular Diagnostic Techniques (methods) |
| 2 | Models, Economic |
| 2 | Military Personnel (education) |
| 2 | Japan (epidemiology) |
| 2 | Italy (epidemiology) |
| 2 | Invasive Pulmonary Aspergillosis (epidemiology) |
| 2 | Interviews as Topic |
| 2 | Injections, Intradermal |
| 2 | Influenza, Human (microbiology) |
| 2 | Influenza in Birds (transmission) |
| 2 | Influenza A virus |
| 2 | Influenza A virus (pathogenicity) |
| 2 | Influenza A virus (classification) |
| 2 | Influenza A Virus, H7N7 Subtype (pathogenicity) |
| 2 | Influenza A Virus, H5N1 Subtype (classification) |
| 2 | Influenza A Virus, H3N2 Subtype (pathogenicity) |
| 2 | Influenza A Virus, H1N1 Subtype (pathogenicity) |
| 2 | Infection Control (methods) |
| 2 | Immunization Programs |
| 2 | Immunization (statistics & numerical data) |
| 2 | Hospitals, University |
| 2 | Hemagglutination Tests (veterinary) |
| 2 | Health Services Needs and Demand |
| 2 | Health Personnel |
| 2 | Health Personnel (psychology) |
| 2 | Haemophilus Vaccines (immunology) |
| 2 | Haemophilus Vaccines (adverse effects) |
| 2 | Haemophilus Vaccines (administration & dosage) |
| 2 | Guideline Adherence (statistics & numerical data) |
| 2 | Germany |
| 2 | General Practitioners |
| 2 | Gastrointestinal Diseases (epidemiology) |
| 2 | France |
| 2 | Follow-Up Studies |
| 2 | Family Practice (standards) |
| 2 | Family Practice (methods) |
| 2 | Extracorporeal Membrane Oxygenation |
| 2 | Evaluation Studies as Topic |
| 2 | Epidemics |
| 2 | England (epidemiology) |
| 2 | Emergency Service, Hospital (statistics & numerical data) |
| 2 | Drug Combinations |
| 2 | Disaster Planning |
| 2 | Diphtheria-Tetanus-Pertussis Vaccine (immunology) |
| 2 | Diphtheria-Tetanus-Pertussis Vaccine (adverse effects) |
| 2 | Diphtheria-Tetanus-Pertussis Vaccine (administration & dosage) |
| 2 | Decision Making |
| 2 | Czech Republic (epidemiology) |
| 2 | Cross Infection (prevention & control) |
| 2 | Croatia |
| 2 | Cost-Benefit Analysis |
| 2 | Communicable Diseases (transmission) |
| 2 | Communicable Disease Control (organization & administration) |
| 2 | Case-Control Studies |
| 2 | Bird Diseases (epidemiology) |
| 2 | Biomarkers (blood) |
| 2 | Austria |
| 2 | Antibodies, Viral (isolation & purification) |
| 2 | Antibodies, Neutralizing (blood) |
| 2 | Anti-Bacterial Agents (therapeutic use) |
| 2 | Anseriformes (virology) |
| 2 | Animal Husbandry |
| 1 | alpha-Tocopherol (adverse effects) |
| 1 | Zoonoses |
| 1 | Zoonoses (transmission) |
| 1 | Zoonoses (epidemiology) |
| 1 | Zanamivir (therapeutic use) |
| 1 | Yersinia enterocolitica (isolation & purification) |
| 1 | World War I |
| 1 | World Health Organization |
| 1 | Workplace |
| 1 | Wales (epidemiology) |
| 1 | Viruses (isolation & purification) |
| 1 | Viruses (classification) |
| 1 | Virus Diseases (veterinary) |
| 1 | Virus Diseases (prevention & control) |
| 1 | Virus Diseases (pathology) |
| 1 | Viral Vaccines |
| 1 | Viral Load (methods) |
| 1 | Ventricular Dysfunction, Right (virology) |
| 1 | Ventricular Dysfunction, Right (therapy) |
| 1 | Ventricular Dysfunction, Right (epidemiology) |
| 1 | Ventricular Dysfunction, Right (diagnostic imaging) |
| 1 | Ventricular Dysfunction, Left (virology) |
| 1 | Ventricular Dysfunction, Left (therapy) |
| 1 | Ventricular Dysfunction, Left (epidemiology) |
| 1 | Ventricular Dysfunction, Left (diagnostic imaging) |
| 1 | Vaginal Smears (statistics & numerical data) |
| 1 | Vaccines, Inactivated (immunology) |
| 1 | Vaccines, Inactivated (administration & dosage) |
| 1 | Vaccines, Conjugate (therapeutic use) |
| 1 | Vaccines, Conjugate (immunology) |
| 1 | Vaccines, Conjugate (adverse effects) |
| 1 | Vaccines, Conjugate (administration & dosage) |
| 1 | Vaccines, Combined (therapeutic use) |
| 1 | Vaccines, Combined (immunology) |
| 1 | Vaccines, Combined (adverse effects) |
| 1 | Vaccines, Attenuated |
| 1 | Vaccines, Attenuated (administration & dosage) |
| 1 | Vaccination (trends) |
| 1 | Vaccination (standards) |
| 1 | Uterine Cervical Neoplasms (prevention & control) |
| 1 | United Kingdom |
| 1 | Uncertainty |
| 1 | Turkeys (virology) |
| 1 | Turkey |
| 1 | Travel (statistics & numerical data) |
| 1 | Transmissible gastroenteritis virus (isolation & purification) |
| 1 | Transmissible gastroenteritis virus (immunology) |
| 1 | Touch |
| 1 | Tobacco Smoke Pollution (prevention & control) |
| 1 | Tobacco Smoke Pollution (legislation & jurisprudence) |
| 1 | Thailand |
| 1 | Text Messaging |
| 1 | Tetanus Toxoid |
| 1 | Tertiary Care Centers |
| 1 | Temperature |
| 1 | Syringes |
| 1 | Swine Diseases (etiology) |
| 1 | Swine Diseases (blood) |
| 1 | Swine (microbiology) |
| 1 | Sweden (epidemiology) |
| 1 | Survival Rate (trends) |
| 1 | Superinfection (etiology) |
| 1 | Superinfection (epidemiology) |
| 1 | Streptococcus pneumoniae (immunology) |
| 1 | Streptococcus pneumoniae (drug effects) |
| 1 | Statistics as Topic |
| 1 | Staphylococcus aureus (isolation & purification) |
| 1 | Staphylococcus aureus (drug effects) |
| 1 | Squalene (adverse effects) |
| 1 | Specimen Handling (standards) |
| 1 | Specimen Handling (methods) |
| 1 | Spain |
| 1 | Spain (epidemiology) |
| 1 | Space-Time Clustering |
| 1 | Social Networking |
| 1 | Smoking Cessation (legislation & jurisprudence) |
| 1 | Smoking (mortality) |
| 1 | Smoking (epidemiology) |
| 1 | Smoking (adverse effects) |
| 1 | Smoke-Free Policy (legislation & jurisprudence) |
| 1 | Slovenia (epidemiology) |
| 1 | Slovakia (epidemiology) |
| 1 | Single-Blind Method |
| 1 | Sex Factors |
| 1 | Severe Acute Respiratory Syndrome (epidemiology) |
| 1 | Serotyping (methods) |
| 1 | Serologic Tests |
| 1 | Sequence Analysis |
| 1 | Sequence Analysis, RNA |
| 1 | Sequence Analysis, DNA (veterinary) |
| 1 | Self Report |
| 1 | Scotland (epidemiology) |
| 1 | Schools |
| 1 | Safety |
| 1 | Safety Management (organization & administration) |
| 1 | SARS Virus |
| 1 | Rural Population |
| 1 | Rotavirus (isolation & purification) |
| 1 | Romania (epidemiology) |
| 1 | Risk Management (organization & administration) |
| 1 | Reverse Transcriptase Polymerase Chain Reaction |
| 1 | Reverse Transcriptase Polymerase Chain Reaction (veterinary) |
| 1 | Reverse Transcriptase Polymerase Chain Reaction (statistics & numerical data) |
| 1 | Restaurants |
| 1 | Respirovirus Infections (prevention & control) |
| 1 | Respirovirus Infections (epidemiology) |
| 1 | Respirovirus (isolation & purification) |
| 1 | Respiratory Tract Infections (veterinary) |
| 1 | Respiratory Tract Infections (prevention & control) |
| 1 | Respiratory Tract Infections (etiology) |
| 1 | Respiratory Tract Diseases (virology) |
| 1 | Respiratory Tract Diseases (veterinary) |
| 1 | Respiratory Tract Diseases (pathology) |
| 1 | Respiratory Tract Diseases (microbiology) |
| 1 | Respiratory Tract Diseases (drug therapy) |
| 1 | Respiratory Tract Diseases (diagnosis) |
| 1 | Respiratory Syncytial Virus, Human (genetics) |
| 1 | Respiratory Syncytial Virus Infections (virology) |
| 1 | Respiratory Syncytial Virus Infections (epidemiology) |
| 1 | Respiratory Distress Syndrome, Adult (virology) |
| 1 | Respiratory Distress Syndrome, Adult (drug therapy) |
| 1 | Reproducibility of Results |
| 1 | Reminder Systems |
| 1 | Registries |
| 1 | Registries (statistics & numerical data) |
| 1 | Real-Time Polymerase Chain Reaction (veterinary) |
| 1 | Reagent Kits, Diagnostic |
| 1 | Reagent Kits, Diagnostic (veterinary) |
| 1 | Reagent Kits, Diagnostic (standards) |
| 1 | Raptors (virology) |
| 1 | ROC Curve |
| 1 | RNA, Ribosomal, 16S (genetics) |
| 1 | Quality-Adjusted Life Years |
| 1 | Quality of Life |
| 1 | Quality of Health Care |
| 1 | Quality of Health Care (organization & administration) |
| 1 | Qualitative Research |
| 1 | Pulmonary Disease, Chronic Obstructive (drug therapy) |
| 1 | Public Health Surveillance |
| 1 | Public Health Practice |
| 1 | Public Health Informatics (methods) |
| 1 | Public Health (statistics & numerical data) |
| 1 | Public Health (economics) |
| 1 | Pseudorabies (immunology) |
| 1 | Protein Conformation |
| 1 | Program Evaluation |
| 1 | Prognosis |
| 1 | Product Surveillance, Postmarketing (methods) |
| 1 | Probiotics (administration & dosage) |
| 1 | Primary Health Care |
| 1 | Primary Health Care (statistics & numerical data) |
| 1 | Primary Health Care (standards) |
| 1 | Primary Health Care (organization & administration) |
| 1 | Preventive Health Services (standards) |
| 1 | Preventive Health Services (economics) |
| 1 | Premature Birth (epidemiology) |
| 1 | Pregnancy Trimesters |
| 1 | Pregnancy Trimester, Third |
| 1 | Pregnancy Complications, Infectious (therapy) |
| 1 | Pregnancy Complications, Infectious (epidemiology) |
| 1 | Pregnancy Complications, Infectious (diagnosis) |
| 1 | Pre-Exposure Prophylaxis (methods) |
| 1 | Practice Patterns, Physicians' (standards) |
| 1 | Poultry (virology) |
| 1 | Postpartum Period |
| 1 | Portugal |
| 1 | Polysorbates (adverse effects) |
| 1 | Polymerase Chain Reaction (methods) |
| 1 | Poland (epidemiology) |
| 1 | Poisson Distribution |
| 1 | Point-of-Care Systems |
| 1 | Pneumonia, Viral (virology) |
| 1 | Pneumonia, Viral (prevention & control) |
| 1 | Pneumonia, Viral (epidemiology) |
| 1 | Pneumonia, Viral (drug therapy) |
| 1 | Pneumonia, Pneumococcal (therapy) |
| 1 | Pneumonia, Pneumococcal (prevention & control) |
| 1 | Pneumonia, Pneumococcal (physiopathology) |
| 1 | Pneumonia, Pneumococcal (epidemiology) |
| 1 | Pneumonia, Pneumococcal (diagnosis) |
| 1 | Pneumonia, Bacterial (drug therapy) |
| 1 | Pneumonia, Bacterial (diagnosis) |
| 1 | Pneumonia of Swine, Mycoplasmal (veterinary) |
| 1 | Pneumonia of Swine, Mycoplasmal (immunology) |
| 1 | Pneumonia of Swine, Mycoplasmal (epidemiology) |
| 1 | Pneumonia (psychology) |
| 1 | Pneumonia (history) |
| 1 | Pneumonia (ethnology) |
| 1 | Pneumococcal Vaccines (therapeutic use) |
| 1 | Pneumococcal Vaccines (immunology) |
| 1 | Pneumococcal Vaccines (adverse effects) |
| 1 | Pneumococcal Vaccines (administration & dosage) |
| 1 | Placebos (administration & dosage) |
| 1 | Phylogeography |
| 1 | Photography (history) |
| 1 | Photography (education) |
| 1 | Pharynx (virology) |
| 1 | Pharmaceutical Preparations (administration & dosage) |
| 1 | Pets |
| 1 | Pertussis Vaccine (therapeutic use) |
| 1 | Pertussis Vaccine (administration & dosage) |
| 1 | Personnel, Hospital |
| 1 | Percutaneous Coronary Intervention (methods) |
| 1 | Perception |
| 1 | Patient-Centered Care (statistics & numerical data) |
| 1 | Patient-Centered Care (organization & administration) |
| 1 | Patient Satisfaction |
| 1 | Patient Safety (standards) |
| 1 | Patient Preference |
| 1 | Patient Acceptance of Health Care (psychology) |
| 1 | Parvoviridae Infections (epidemiology) |
| 1 | Parvoviridae Infections (diagnosis) |
| 1 | Paris (epidemiology) |
| 1 | Papanicolaou Test |
| 1 | Pandemics (economics) |
| 1 | Ownership (statistics & numerical data) |
| 1 | Oseltamivir |
| 1 | Oseltamivir (administration & dosage) |
| 1 | Orthomyxoviridae Infections (microbiology) |
| 1 | Orthomyxoviridae Infections (immunology) |
| 1 | Orthomyxoviridae (pathogenicity) |
| 1 | Orthomyxoviridae (immunology) |
| 1 | Orthomyxoviridae (growth & development) |
| 1 | Orthomyxoviridae (genetics) |
| 1 | Orthomyxoviridae (classification) |
| 1 | Opportunistic Infections (microbiology) |
| 1 | Online Systems |
| 1 | Nursing Homes (statistics & numerical data) |
| 1 | Nucleic Acid Amplification Techniques |
| 1 | Norway (epidemiology) |
| 1 | Northern Ireland (epidemiology) |
| 1 | Nonlinear Dynamics |
| 1 | Nocardia Infections (diagnosis) |
| 1 | Nocardia (isolation & purification) |
| 1 | Nocardia (genetics) |
| 1 | Newspapers as Topic |
| 1 | Neutralization Tests |
| 1 | Neuraminidase (metabolism) |
| 1 | Neuraminidase (immunology) |
| 1 | Nervous System Diseases (pathology) |
| 1 | Nervous System Diseases (epidemiology) |
| 1 | Nervous System Diseases (drug therapy) |
| 1 | Nervous System Diseases (diagnosis) |
| 1 | National Health Programs |
| 1 | National Health Programs (legislation & jurisprudence) |
| 1 | Nasopharynx (microbiology) |
| 1 | Myocardial Infarction (surgery) |
| 1 | Myocardial Infarction (prevention & control) |
| 1 | Myocardial Infarction (mortality) |
| 1 | Myocardial Infarction (etiology) |
| 1 | Myocardial Infarction (epidemiology) |
