| 553 | Humans |
| 303 | Germany |
| 295 | Germany (epidemiology) |
| 254 | Female |
| 249 | Male |
| 220 | Influenza, Human (epidemiology) |
| 213 | Influenza, Human (prevention & control) |
| 211 | Adult |
| 202 | Middle Aged |
| 165 | Aged |
| 158 | Adolescent |
| 151 | Child |
| 124 | Child, Preschool |
| 122 | Influenza Vaccines (administration & dosage) |
| 118 | Animals |
| 113 | Young Adult |
| 108 | Infant |
| 80 | Risk Factors |
| 76 | Influenza, Human (virology) |
| 75 | Aged, 80 and over |
| 74 | Seasons |
| 57 | Incidence |
| 55 | Influenza, Human (diagnosis) |
| 54 | Vaccination (statistics & numerical data) |
| 51 | Prevalence |
| 51 | Infant, Newborn |
| 48 | Influenza Vaccines (immunology) |
| 47 | Influenza, Human (immunology) |
| 47 | Influenza A Virus, H1N1 Subtype |
| 45 | Surveys and Questionnaires |
| 41 | Influenza, Human (transmission) |
| 41 | Influenza in Birds (epidemiology) |
| 40 | Influenza, Human (mortality) |
| 40 | Cross-Sectional Studies |
| 39 | Disease Outbreaks (prevention & control) |
| 39 | Antibodies, Viral (blood) |
| 39 | Age Factors |
| 37 | Influenza Vaccines (therapeutic use) |
| 37 | Disease Outbreaks |
| 35 | Influenza A virus (isolation & purification) |
| 33 | Influenza Vaccines (adverse effects) |
| 32 | Phylogeny |
| 32 | Influenza A Virus, H1N1 Subtype (isolation & purification) |
| 32 | Influenza A Virus, H1N1 Subtype (immunology) |
| 31 | Population Surveillance |
| 31 | Influenza in Birds (virology) |
| 31 | Disease Outbreaks (statistics & numerical data) |
| 31 | Antiviral Agents (therapeutic use) |
| 30 | Pandemics |
| 29 | Treatment Outcome |
| 29 | Risk Assessment |
| 29 | Respiratory Tract Infections (epidemiology) |
| 29 | Orthomyxoviridae Infections (veterinary) |
| 29 | Berlin |
| 29 | Age Distribution |
| 27 | Influenza, Human (drug therapy) |
| 26 | Vaccination |
| 26 | Population Surveillance (methods) |
| 25 | Retrospective Studies |
| 25 | Prospective Studies |
| 25 | Health Knowledge, Attitudes, Practice |
| 24 | Time Factors |
| 24 | Practice Guidelines as Topic |
| 24 | Orthomyxoviridae Infections (epidemiology) |
| 24 | Disease Outbreaks (veterinary) |
| 23 | Swine |
| 22 | Influenza A virus (genetics) |
| 21 | Influenza Vaccines |
| 21 | Attitude of Health Personnel |
| 20 | Seroepidemiologic Studies |
| 20 | Respiratory Tract Infections (virology) |
| 20 | Pregnancy |
| 20 | Mass Vaccination (statistics & numerical data) |
| 20 | Influenza, Human (complications) |
| 20 | Influenza A virus (immunology) |
| 20 | Influenza A virus (classification) |
| 20 | Hemagglutination Inhibition Tests |
| 20 | Birds |
| 19 | Swine Diseases (virology) |
| 19 | Pandemics (prevention & control) |
| 19 | Health Surveys |
| 19 | Case-Control Studies |
| 18 | Orthomyxoviridae Infections (virology) |
| 18 | Influenza, Human (therapy) |
| 18 | Influenza A Virus, H1N1 Subtype (genetics) |
| 17 | Sensitivity and Specificity |
| 17 | Risk Assessment (methods) |
| 17 | Hospitalization (statistics & numerical data) |
| 17 | Cross Infection (prevention & control) |
| 16 | Sex Distribution |
| 16 | Sentinel Surveillance |
| 16 | Pandemics (statistics & numerical data) |
| 16 | Cross Infection (epidemiology) |
| 15 | Influenza in Birds (transmission) |
| 15 | Acute Disease |
| 14 | Swine Diseases (epidemiology) |
| 14 | Immunization Schedule |
| 14 | Comorbidity |
| 14 | Cause of Death |
| 13 | Respiratory Tract Infections (diagnosis) |
| 13 | Molecular Sequence Data |
| 13 | Influenza, Human (economics) |
| 13 | Influenza A Virus, H5N1 Subtype (isolation & purification) |
| 13 | Hemagglutinin Glycoproteins, Influenza Virus (genetics) |
| 13 | Cohort Studies |
| 12 | Vaccination (standards) |
| 12 | Vaccination (methods) |
| 12 | Travel |
| 12 | Reverse Transcriptase Polymerase Chain Reaction |
| 12 | Pneumococcal Vaccines (administration & dosage) |
| 12 | Patient Acceptance of Health Care (statistics & numerical data) |
| 12 | Neuraminidase (genetics) |
| 12 | Neuraminidase (antagonists & inhibitors) |
| 12 | Influenza, Human (history) |
| 12 | Influenza B virus (isolation & purification) |
| 12 | Influenza A Virus, H3N2 Subtype (isolation & purification) |
| 12 | Influenza A Virus, H1N1 Subtype (pathogenicity) |
| 12 | History, 20th Century |
| 12 | Anti-Bacterial Agents (therapeutic use) |
| 11 | Viruses (isolation & purification) |
| 11 | Virus Diseases (epidemiology) |
| 11 | Vaccination (psychology) |
| 11 | Oseltamivir (therapeutic use) |
| 11 | Models, Statistical |
| 11 | Logistic Models |
| 11 | Influenza, Human (nursing) |
| 11 | Influenza Vaccines (supply & distribution) |
| 11 | Influenza A Virus, H3N2 Subtype (immunology) |
| 11 | Genetic Variation |
| 11 | Cost-Benefit Analysis |
| 10 | Vaccination (adverse effects) |
| 10 | Survival Rate |
| 10 | Survival Analysis |
| 10 | Respiratory Syncytial Virus Infections (epidemiology) |
| 10 | Pneumococcal Vaccines |
| 10 | Pneumococcal Infections (prevention & control) |
| 10 | Netherlands (epidemiology) |
| 10 | Influenza, Human |
| 10 | Influenza, Human (pathology) |
| 10 | Influenza Vaccines (economics) |
| 10 | Influenza B virus (immunology) |
| 10 | Influenza A virus |
| 10 | Influenza A virus (pathogenicity) |
| 10 | Influenza A Virus, H3N2 Subtype (genetics) |
| 10 | Hospitals, University |
| 10 | Cost of Illness |
| 10 | Communicable Diseases (epidemiology) |
| 10 | Animals, Wild |
| 9 | World Health Organization |
| 9 | Reassortant Viruses (genetics) |
| 9 | Models, Theoretical |
| 9 | Immunization, Secondary |
| 9 | Immunization Programs (statistics & numerical data) |
| 9 | Hospitalization |
| 9 | Health Personnel |
| 9 | Forecasting |
| 9 | Europe |
| 9 | Diagnosis, Differential |
| 9 | Communicable Disease Control (organization & administration) |
| 8 | Vaccination (trends) |
| 8 | Switzerland (epidemiology) |
| 8 | Sequence Analysis, DNA |
| 8 | Risk |
| 8 | Reproducibility of Results |
| 8 | Poultry |
| 8 | Patient Education as Topic |
| 8 | Orthomyxoviridae (immunology) |
| 8 | Occupational Diseases (prevention & control) |
| 8 | Nasopharynx (virology) |
| 8 | Medical Staff, Hospital (statistics & numerical data) |
| 8 | Interviews as Topic |
| 8 | Influenza in Birds (pathology) |
| 8 | Influenza Vaccines (standards) |
| 8 | Influenza A Virus, H5N1 Subtype (genetics) |
| 8 | Influenza A Virus, H1N1 Subtype (classification) |
| 8 | Immunization Programs |
| 8 | Germany, West |
| 8 | Family Characteristics |
| 8 | Epidemics |
| 8 | Cross Infection (transmission) |
| 8 | Chickens |
| 8 | Birds (virology) |
| 8 | Base Sequence |
| 8 | Antiviral Agents (pharmacology) |
| 8 | Animals, Wild (virology) |
| 7 | Virus Diseases (virology) |
| 7 | Virus Diseases (diagnosis) |
| 7 | Virulence |
| 7 | Vaccination (legislation & jurisprudence) |
| 7 | United States |
| 7 | United States (epidemiology) |
| 7 | Sex Factors |
| 7 | Reverse Transcriptase Polymerase Chain Reaction (methods) |
| 7 | RNA, Viral (genetics) |
| 7 | Polymerase Chain Reaction |
| 7 | Paramyxoviridae Infections (epidemiology) |
| 7 | Orthomyxoviridae |
| 7 | Orthomyxoviridae (isolation & purification) |
| 7 | Italy (epidemiology) |
| 7 | Internet |
| 7 | Influenza, Human (psychology) |
| 7 | Influenza, Human (blood) |
| 7 | Influenza A Virus, H5N1 Subtype (pathogenicity) |
| 7 | Infectious Disease Transmission, Professional-to-Patient (prevention & control) |
| 7 | Germany, East |
| 7 | Dogs |
| 7 | Computer Simulation |
| 7 | Community-Acquired Infections (epidemiology) |
| 7 | Communicable Diseases, Emerging (epidemiology) |
| 7 | Communicable Disease Control (methods) |
| 7 | Cats |
| 7 | Berlin (epidemiology) |
| 7 | Antigens, Viral (immunology) |
| 7 | Amino Acid Sequence |
| 6 | Virology (methods) |
| 6 | Viral Vaccines (administration & dosage) |
| 6 | Utilization Review |
| 6 | Species Specificity |
| 6 | Severity of Illness Index |
| 6 | Respiratory Syncytial Virus Infections (virology) |
| 6 | RNA, Viral (analysis) |
| 6 | Public Health |
| 6 | Orthomyxoviridae Infections (immunology) |
| 6 | Orthomyxoviridae (classification) |
| 6 | Mass Vaccination (standards) |
| 6 | Mass Vaccination (methods) |
| 6 | Influenza, Human (physiopathology) |
| 6 | Influenza in Birds (prevention & control) |
| 6 | Influenza A Virus, H5N1 Subtype |
| 6 | Hygiene |
| 6 | Health Care Surveys |
| 6 | Guideline Adherence |
| 6 | France (epidemiology) |
| 6 | Follow-Up Studies |
| 6 | European Union |
| 6 | Drug Resistance, Viral |
| 6 | Data Collection |
| 6 | Cross Infection (mortality) |
| 6 | Cluster Analysis |
| 6 | Chick Embryo |
| 6 | Austria (epidemiology) |
| 6 | Antibody Formation (immunology) |
| 6 | Absenteeism |
| 5 | Zoonoses |
| 5 | Whooping Cough (prevention & control) |
| 5 | Vaccination (economics) |
| 5 | United Kingdom (epidemiology) |
| 5 | Telephone |
| 5 | Real-Time Polymerase Chain Reaction |
| 5 | Quality-Adjusted Life Years |
| 5 | Prognosis |
| 5 | Primary Health Care |
| 5 | Poultry Diseases (virology) |
| 5 | Poultry Diseases (epidemiology) |
| 5 | Poultry (virology) |
| 5 | Polymerase Chain Reaction (methods) |
| 5 | Pneumonia, Viral (mortality) |
| 5 | Pneumonia, Viral (diagnosis) |
| 5 | Pneumococcal Infections (epidemiology) |
| 5 | Pilot Projects |
| 5 | Pharynx (virology) |
| 5 | Patient Compliance (statistics & numerical data) |
| 5 | Patient Acceptance of Health Care |
| 5 | Pandemics (history) |
| 5 | Oseltamivir (pharmacology) |
| 5 | Odds Ratio |
| 5 | Occupational Diseases (epidemiology) |
| 5 | National Health Programs |
| 5 | Multiplex Polymerase Chain Reaction |
| 5 | Mortality (trends) |
| 5 | Models, Biological |
| 5 | Mass Vaccination |
| 5 | Mass Vaccination (trends) |
| 5 | Mass Vaccination (organization & administration) |
| 5 | Influenza, Human (etiology) |
| 5 | Influenza B virus (genetics) |
| 5 | Influenza A virus (drug effects) |
| 5 | Influenza A Virus, H3N2 Subtype |
| 5 | Influenza A Virus, H3N2 Subtype (drug effects) |
| 5 | Influenza A Virus, H3N2 Subtype (classification) |
| 5 | Influenza A Virus, H1N1 Subtype (physiology) |
| 5 | Influenza A Virus, H1N1 Subtype (drug effects) |
| 5 | Hospitals |
| 5 | Horses |
| 5 | Health Status |
| 5 | Health Promotion (statistics & numerical data) |
| 5 | Health Personnel (statistics & numerical data) |
| 5 | Guideline Adherence (statistics & numerical data) |
| 5 | Genotype |
| 5 | Family Health |
| 5 | Ducks (virology) |
| 5 | Disease Outbreaks (history) |
| 5 | Disaster Planning (organization & administration) |
| 5 | Databases, Factual |
| 5 | Cross Infection (virology) |
| 5 | Community-Acquired Infections (diagnosis) |
| 5 | Communicable Disease Control (statistics & numerical data) |
| 5 | Cloaca (virology) |
| 5 | Cell Line |
| 5 | Cat Diseases (epidemiology) |
| 5 | Bird Diseases (virology) |
| 5 | Bird Diseases (epidemiology) |
| 5 | Belgium (epidemiology) |
| 5 | Austria |
| 5 | Antiviral Agents (administration & dosage) |
| 5 | Amino Acid Substitution |
| 5 | Adjuvants, Immunologic (adverse effects) |
| 5 | Adjuvants, Immunologic (administration & dosage) |
| 4 | Zanamivir (pharmacology) |
| 4 | Viruses (genetics) |
| 4 | Virus Shedding |
| 4 | Vaccines, Inactivated (immunology) |
| 4 | Vaccines, Combined (administration & dosage) |
| 4 | Vaccines, Attenuated (administration & dosage) |
| 4 | Vaccines (administration & dosage) |
| 4 | Turkeys (virology) |
| 4 | Trachea (virology) |
| 4 | Tetanus Toxoid (administration & dosage) |
| 4 | Temperature |
| 4 | Swine (virology) |
| 4 | Serologic Tests |
| 4 | Sequence Alignment |
| 4 | Sentinel Surveillance (veterinary) |
| 4 | Safety |
| 4 | Risk Management (methods) |
| 4 | Reverse Transcriptase Polymerase Chain Reaction (veterinary) |
| 4 | Respiratory Tract Diseases (epidemiology) |
| 4 | Registries |
| 4 | Public Opinion |
| 4 | Primary Health Care (statistics & numerical data) |
| 4 | Practice Patterns, Physicians' |
| 4 | Poultry Diseases (prevention & control) |
| 4 | Portugal (epidemiology) |
| 4 | Population Density |
| 4 | Polymerase Chain Reaction (veterinary) |
| 4 | Pneumonia, Pneumococcal (prevention & control) |
| 4 | Pneumonia (epidemiology) |
| 4 | Physician's Role |
| 4 | Particle Size |
| 4 | Netherlands |
| 4 | Mutation |
| 4 | Microbial Sensitivity Tests |
| 4 | Internationality |
| 4 | Influenza, Human (classification) |
| 4 | Influenza in Birds (diagnosis) |
| 4 | Influenza A Virus, H5N1 Subtype (classification) |
| 4 | Influenza A Virus, H1N2 Subtype (isolation & purification) |
| 4 | Infectious Disease Transmission, Patient-to-Professional (prevention & control) |
| 4 | Immunoglobulin G (blood) |
| 4 | Horse Diseases (epidemiology) |
| 4 | Hemagglutination Inhibition Tests (veterinary) |
| 4 | Health Promotion (methods) |
| 4 | Health Policy |
| 4 | Health Behavior |
| 4 | Haemophilus Vaccines (administration & dosage) |
| 4 | Global Health |
| 4 | Genome, Viral |
| 4 | Genes, Viral |
| 4 | General Practice |
| 4 | France |
| 4 | Feces (virology) |
| 4 | Evidence-Based Medicine |
| 4 | Epidemiological Monitoring |
| 4 | Enzyme-Linked Immunosorbent Assay (veterinary) |
| 4 | Dog Diseases (epidemiology) |
| 4 | Disease Notification (statistics & numerical data) |
| 4 | Diphtheria-Tetanus-Pertussis Vaccine (administration & dosage) |
| 4 | Cross Reactions |
| 4 | Cross Infection (diagnosis) |
| 4 | Critical Care |
| 4 | Complement Fixation Tests |
| 4 | Community-Acquired Infections (mortality) |
| 4 | Community-Acquired Infections (drug therapy) |
| 4 | Communicable Diseases, Emerging (virology) |
| 4 | Communicable Diseases, Emerging (veterinary) |
| 4 | Communicable Disease Control (standards) |
| 4 | Cardiovascular Diseases (mortality) |
| 4 | Bacterial Vaccines (administration & dosage) |
| 4 | Bacterial Infections (microbiology) |
| 4 | Bacteria (isolation & purification) |
| 4 | Attitude to Health |
| 4 | Antigens, Viral (genetics) |
| 4 | Antibodies, Viral (immunology) |
| 4 | Antibodies, Bacterial (blood) |
| 4 | Acute Disease (epidemiology) |
| 3 | Zanamivir (therapeutic use) |
| 3 | World War I |
| 3 | Virus Diseases (veterinary) |
| 3 | Virus Diseases (therapy) |
| 3 | Virus Diseases (prevention & control) |
| 3 | Virus Cultivation (methods) |
| 3 | Viral Proteins (genetics) |
| 3 | Viral Matrix Proteins (genetics) |
| 3 | Viral Load |
| 3 | Vaccines, Inactivated (adverse effects) |
| 3 | Vaccines, Inactivated (administration & dosage) |
| 3 | Vaccines, Combined (immunology) |
| 3 | Vaccines, Attenuated (standards) |
| 3 | Vaccination (ethics) |
| 3 | Travel (statistics & numerical data) |
| 3 | Tetanus (prevention & control) |
| 3 | Tertiary Care Centers |
| 3 | Swine Diseases (transmission) |
| 3 | Sweden (epidemiology) |
| 3 | Spain (epidemiology) |
| 3 | Societies |
| 3 | Serotyping |
| 3 | Sequence Homology |
| 3 | Self Report |
| 3 | Rotavirus Vaccines (administration & dosage) |
| 3 | Risk Assessment (statistics & numerical data) |
| 3 | Respiratory Tract Infections (therapy) |
| 3 | Respiratory Tract Infections (microbiology) |
| 3 | Respiratory Tract Diseases (mortality) |
| 3 | Respiratory Syncytial Viruses (isolation & purification) |
| 3 | Respiratory Syncytial Virus, Human (isolation & purification) |
| 3 | Respiratory Syncytial Virus Infections (diagnosis) |
| 3 | Respiration, Artificial |
| 3 | Residence Characteristics |
| 3 | Regression Analysis |
| 3 | Reference Standards |
| 3 | Reassortant Viruses (isolation & purification) |
| 3 | Reassortant Viruses (classification) |
| 3 | Randomized Controlled Trials as Topic |
| 3 | Quality Control |
| 3 | Public Health Administration |
| 3 | Product Surveillance, Postmarketing |
| 3 | Pregnancy Complications, Infectious (prevention & control) |
| 3 | Pregnancy Complications, Infectious (epidemiology) |
| 3 | Practice Patterns, Physicians' (statistics & numerical data) |
| 3 | Poliovirus Vaccine, Inactivated (immunology) |
| 3 | Poliovirus Vaccine, Inactivated (administration & dosage) |
| 3 | Pneumonia, Viral (epidemiology) |
| 3 | Pneumonia, Viral (drug therapy) |
| 3 | Pneumonia, Bacterial (mortality) |
| 3 | Pneumonia, Bacterial (epidemiology) |
| 3 | Pneumococcal Vaccines (immunology) |
| 3 | Picornaviridae Infections (epidemiology) |
| 3 | Pertussis Vaccine (administration & dosage) |
| 3 | Patient Selection |
| 3 | Patient Participation (statistics & numerical data) |
| 3 | Patient Isolation |
| 3 | Particulate Matter (analysis) |
| 3 | Paramyxoviridae Infections (virology) |
| 3 | Papillomavirus Vaccines (administration & dosage) |
| 3 | Orthomyxoviridae Infections (transmission) |
| 3 | Orthomyxoviridae Infections (prevention & control) |
| 3 | Orthomyxoviridae (growth & development) |
| 3 | Orthomyxoviridae (genetics) |
| 3 | Occupational Exposure |
| 3 | Nursing Staff, Hospital (statistics & numerical data) |
| 3 | Newcastle disease virus (isolation & purification) |
| 3 | Newcastle Disease (epidemiology) |
| 3 | Neutralization Tests |
| 3 | Neuraminidase (immunology) |
| 3 | Neuraminidase (chemistry) |
| 3 | Nasopharynx (microbiology) |
| 3 | Narcolepsy (epidemiology) |
| 3 | Mutation, Missense |
| 3 | Multivariate Analysis |
| 3 | Multiple Sclerosis (immunology) |
| 3 | Multiple Sclerosis (epidemiology) |
| 3 | Motivation |
| 3 | Mortality |
| 3 | Molecular Epidemiology |
| 3 | Molecular Diagnostic Techniques (methods) |
| 3 | Models, Organizational |
| 3 | Models, Economic |
| 3 | Models, Econometric |
| 3 | Mexico |
| 3 | Metapneumovirus (isolation & purification) |
| 3 | Medical Staff, Hospital (psychology) |
| 3 | Meat (virology) |
| 3 | Mandatory Reporting |
| 3 | Lung (pathology) |
| 3 | Length of Stay |
| 3 | Intensive Care Units |
| 3 | Information Dissemination (methods) |
| 3 | Influenza in Birds (mortality) |
| 3 | Influenza A Virus, H7N7 Subtype (pathogenicity) |
| 3 | Influenza A Virus, H5N8 Subtype (pathogenicity) |
| 3 | Influenza A Virus, H5N1 Subtype (immunology) |
| 3 | Influenza A Virus, H1N2 Subtype (genetics) |
| 3 | Influenza A Virus, H1N2 Subtype (classification) |
| 3 | Infection Control |
| 3 | Immunosuppressive Agents (therapeutic use) |
| 3 | Immunization |
| 3 | Immunization Programs (organization & administration) |
| 3 | Immunization (adverse effects) |
| 3 | Immune Sera |
| 3 | Humidity |
| 3 | History, 19th Century |
| 3 | Hepatitis B Vaccines (administration & dosage) |
| 3 | Hemagglutinins, Viral (genetics) |
| 3 | Hemagglutinins (genetics) |
| 3 | Hemagglutinin Glycoproteins, Influenza Virus (chemistry) |
| 3 | Health Services Needs and Demand (trends) |
| 3 | Health Promotion |
| 3 | Health Planning Guidelines |
| 3 | Health Personnel (psychology) |
