| 603 | Germany |
| 556 | Humans |
| 418 | Influenza, Human |
| 255 | Female |
| 250 | Male |
| 216 | Influenza Vaccines |
| 212 | Adult |
| 203 | Middle Aged |
| 165 | Aged |
| 159 | Adolescent |
| 152 | Child |
| 125 | Child, Preschool |
| 124 | Influenza A Virus, H1N1 Subtype |
| 122 | Vaccination |
| 121 | Disease Outbreaks |
| 119 | Animals |
| 113 | Young Adult |
| 110 | Infant |
| 80 | Risk Factors |
| 78 | Influenza A virus |
| 75 | Seasons |
| 75 | Aged, 80 and over |
| 59 | Pandemics |
| 57 | Population Surveillance |
| 57 | Incidence |
| 52 | Influenza in Birds |
| 52 | Infant, Newborn |
| 51 | Prevalence |
| 48 | Risk Assessment |
| 46 | Antibodies, Viral |
| 45 | Surveys and Questionnaires |
| 43 | Antiviral Agents |
| 40 | Cross-Sectional Studies |
| 39 | Age Factors |
| 37 | Respiratory Tract Infections |
| 37 | Mass Vaccination |
| 36 | Orthomyxoviridae Infections |
| 36 | Berlin |
| 33 | Birds |
| 32 | Phylogeny |
| 30 | Influenza A Virus, H3N2 Subtype |
| 29 | Treatment Outcome |
| 29 | Communicable Disease Control |
| 29 | Age Distribution |
| 28 | Swine |
| 28 | Hospitalization |
| 28 | Cross Infection |
| 27 | Retrospective Studies |
| 26 | Neuraminidase |
| 25 | Prospective Studies |
| 25 | Influenza B virus |
| 25 | Influenza A Virus, H5N1 Subtype |
| 25 | Health Knowledge, Attitudes, Practice |
| 24 | Time Factors |
| 24 | Practice Guidelines as Topic |
| 24 | Hemagglutination Inhibition Tests |
| 23 | Pneumococcal Vaccines |
| 23 | Orthomyxoviridae |
| 21 | Swine Diseases |
| 21 | Sentinel Surveillance |
| 21 | Reverse Transcriptase Polymerase Chain Reaction |
| 21 | Health Surveys |
| 21 | Attitude of Health Personnel |
| 20 | Virus Diseases |
| 20 | Seroepidemiologic Studies |
| 20 | Pregnancy |
| 20 | Immunization Programs |
| 19 | Case-Control Studies |
| 19 | Animals, Wild |
| 19 | Acute Disease |
| 18 | Oseltamivir |
| 18 | Health Personnel |
| 18 | Communicable Diseases |
| 17 | Sensitivity and Specificity |
| 17 | Patient Acceptance of Health Care |
| 16 | Travel |
| 16 | Sex Distribution |
| 16 | RNA, Viral |
| 16 | Polymerase Chain Reaction |
| 16 | Hemagglutinin Glycoproteins, Influenza Virus |
| 14 | United States |
| 14 | Poultry |
| 14 | Netherlands |
| 14 | Immunization Schedule |
| 14 | Hospitals, University |
| 14 | Comorbidity |
| 14 | Cause of Death |
| 14 | Anti-Bacterial Agents |
| 13 | Pneumococcal Infections |
| 13 | Molecular Sequence Data |
| 13 | Health Promotion |
| 13 | Community-Acquired Infections |
| 13 | Cohort Studies |
| 13 | Adjuvants, Immunologic |
| 12 | Public Health |
| 12 | History, 20th Century |
| 12 | Europe |
| 12 | Chickens |
| 12 | Antigens, Viral |
| 11 | Zoonoses |
| 11 | Viruses |
| 11 | Respiratory Syncytial Virus Infections |
| 11 | National Health Programs |
| 11 | Models, Statistical |
| 11 | Logistic Models |
| 11 | Immunization, Secondary |
| 11 | Guideline Adherence |
| 11 | Genetic Variation |
| 11 | Cost-Benefit Analysis |
| 11 | Austria |
| 10 | Survival Rate |
| 10 | Survival Analysis |
| 10 | Nasopharynx |
| 10 | France |
| 10 | Epidemics |
| 10 | Ducks |
| 10 | Cost of Illness |
| 9 | World Health Organization |
| 9 | Vaccines, Attenuated |
| 9 | Switzerland |
| 9 | Sequence Analysis, DNA |
| 9 | Reassortant Viruses |
| 9 | Real-Time Polymerase Chain Reaction |
| 9 | Primary Health Care |
| 9 | Poultry Diseases |
| 9 | Pneumonia, Viral |
| 9 | Paramyxoviridae Infections |
| 9 | Mortality |
| 9 | Models, Theoretical |
| 9 | Medical Staff, Hospital |
| 9 | Interviews as Topic |
| 9 | Forecasting |
| 9 | Disease Notification |
| 9 | Diagnosis, Differential |
| 9 | Communicable Diseases, Emerging |
| 8 | Zanamivir |
| 8 | Utilization Review |
| 8 | Risk |
| 8 | Reproducibility of Results |
| 8 | Practice Patterns, Physicians' |
| 8 | Pneumonia |
| 8 | Patient Education as Topic |
| 8 | Occupational Diseases |
| 8 | Italy |
| 8 | Immunization |
| 8 | Germany, West |
| 8 | Family Characteristics |
| 8 | Drug Resistance, Viral |
| 8 | Base Sequence |
| 8 | Antibody Formation |
| 7 | Whooping Cough |
| 7 | Virulence |
| 7 | Virology |
| 7 | Viral Vaccines |
| 7 | Vaccines, Inactivated |
| 7 | United Kingdom |
| 7 | Sex Factors |
| 7 | Patient Compliance |
| 7 | Multiplex Polymerase Chain Reaction |
| 7 | Internet |
| 7 | Infectious Disease Transmission, Professional-to-Patient |
| 7 | Hygiene |
| 7 | Health Planning |
| 7 | Health Care Surveys |
| 7 | Germany, East |
| 7 | European Union |
| 7 | Enzyme-Linked Immunosorbent Assay |
| 7 | Dogs |
| 7 | Disease Reservoirs |
| 7 | Disaster Planning |
| 7 | Data Collection |
| 7 | Computer Simulation |
| 7 | Chronic Disease |
| 7 | Cats |
| 7 | Belgium |
| 7 | Bacterial Infections |
| 7 | Amino Acid Substitution |
| 7 | Amino Acid Sequence |
| 6 | Vaccines |
| 6 | Species Specificity |
| 6 | Severity of Illness Index |
| 6 | Respiratory Tract Diseases |
| 6 | Pneumonia, Bacterial |
| 6 | Pertussis Vaccine |
| 6 | Nursing Staff, Hospital |
| 6 | Intensive Care Units |
| 6 | Influenza A Virus, H7N7 Subtype |
| 6 | Influenza A Virus, H1N2 Subtype |
| 6 | Infectious Disease Transmission, Patient-to-Professional |
| 6 | Hospitals |
| 6 | Horses |
| 6 | Hemagglutinins, Viral |
| 6 | Health Services Accessibility |
| 6 | Health Policy |
| 6 | Health Care Costs |
| 6 | HIV Infections |
| 6 | Follow-Up Studies |
| 6 | Databases, Factual |
| 6 | Coinfection |
| 6 | Cluster Analysis |
| 6 | Chick Embryo |
| 6 | Cat Diseases |
| 6 | Cardiovascular Diseases |
| 6 | Bird Diseases |
| 6 | Animal Husbandry |
| 6 | Absenteeism |
| 5 | Virus Shedding |
| 5 | Turkeys |
| 5 | Tetanus Toxoid |
| 5 | Telephone |
| 5 | Students, Medical |
| 5 | Serologic Tests |
| 5 | Safety |
| 5 | Respiratory Syncytial Viruses |
| 5 | Respiratory Distress Syndrome, Adult |
| 5 | Quality-Adjusted Life Years |
| 5 | Public Opinion |
| 5 | Prognosis |
| 5 | Pregnancy Complications, Infectious |
| 5 | Pneumonia, Pneumococcal |
| 5 | Pilot Projects |
| 5 | Physicians |
| 5 | Pharynx |
| 5 | Personnel, Hospital |
| 5 | Odds Ratio |
| 5 | Occupational Exposure |
| 5 | Molecular Epidemiology |
| 5 | Molecular Diagnostic Techniques |
| 5 | Models, Biological |
| 5 | Mexico |
| 5 | Metapneumovirus |
| 5 | Lung |
| 5 | Immunoglobulin G |
| 5 | Hepatitis B Vaccines |
| 5 | Health Status |
| 5 | Genotype |
| 5 | Genome, Viral |
| 5 | Genes, Viral |
| 5 | General Practice |
| 5 | Family Health |
| 5 | Epidemiology |
| 5 | Enzyme Inhibitors |
| 5 | Environmental Monitoring |
| 5 | Critical Care |
| 5 | Cloaca |
| 5 | Cell Line |
| 5 | Anseriformes |
| 5 | Ambulatory Care |
| 5 | Adenoviridae |
| 5 | Adenoviridae Infections |
| 4 | Virus Cultivation |
| 4 | Viral Load |
| 4 | Vaccines, Combined |
| 4 | Trachea |
| 4 | Tetanus |
| 4 | Temperature |
| 4 | Sweden |
| 4 | Spain |
| 4 | Societies, Medical |
| 4 | Smoking |
| 4 | Serotyping |
| 4 | Sequence Alignment |
| 4 | Risk Management |
| 4 | Registries |
| 4 | Referral and Consultation |
| 4 | Reagent Kits, Diagnostic |
| 4 | Product Surveillance, Postmarketing |
| 4 | Portugal |
| 4 | Population Density |
| 4 | Physician's Role |
| 4 | Particulate Matter |
| 4 | Particle Size |
| 4 | Papillomavirus Vaccines |
| 4 | Outpatients |
| 4 | Outcome Assessment, Health Care |
| 4 | Narcolepsy |
| 4 | Mutation |
| 4 | Multiple Sclerosis |
| 4 | Morbidity |
| 4 | Models, Organizational |
| 4 | Microbial Sensitivity Tests |
| 4 | Masks |
| 4 | Internationality |
| 4 | International Classification of Diseases |
| 4 | Intensive Care Units, Pediatric |
| 4 | Information Dissemination |
| 4 | Influenzavirus A |
| 4 | Influenza A Virus, H5N8 Subtype |
| 4 | Infection Control |
| 4 | Immunocompromised Host |
| 4 | Horse Diseases |
| 4 | Hemagglutinins |
| 4 | Health Behavior |
| 4 | Hand Disinfection |
| 4 | Haemophilus Vaccines |
| 4 | Global Health |
| 4 | General Practitioners |
| 4 | Geese |
| 4 | Feces |
| 4 | Family Practice |
| 4 | Extracorporeal Membrane Oxygenation |
| 4 | Evidence-Based Medicine |
| 4 | Epidemiological Monitoring |
| 4 | Dog Diseases |
| 4 | Diphtheria-Tetanus-Pertussis Vaccine |
| 4 | Cross Reactions |
| 4 | Costs and Cost Analysis |
| 4 | Complement Fixation Tests |
| 4 | Common Cold |
| 4 | Blood Donors |
| 4 | Bacterial Vaccines |
| 4 | Bacteria |
| 4 | Attitude to Health |
| 4 | Antibodies |
| 4 | Antibodies, Bacterial |
| 4 | Amantadine |
| 4 | Air Pollutants |
| 3 | World War I |
| 3 | Viral Proteins |
| 3 | Viral Matrix Proteins |
| 3 | Vaccination Coverage |
| 3 | Tertiary Care Centers |
| 3 | Squalene |
| 3 | Societies |
| 3 | Sequence Homology |
| 3 | Self Report |
| 3 | Rotavirus Vaccines |
| 3 | Rotavirus Infections |
| 3 | Rheumatology |
| 3 | Rheumatic Diseases |
| 3 | Respiratory Syncytial Virus, Human |
| 3 | Respiration, Artificial |
| 3 | Residence Characteristics |
| 3 | Reminder Systems |
| 3 | Regression Analysis |
| 3 | Reference Standards |
| 3 | Randomized Controlled Trials as Topic |
| 3 | Quality Control |
| 3 | Public Health Administration |
| 3 | Poliovirus Vaccine, Inactivated |
| 3 | Picornaviridae Infections |
| 3 | Pharyngitis |
| 3 | Pediatrics |
| 3 | Patient Selection |
| 3 | Patient Participation |
| 3 | Patient Isolation |
| 3 | Patient Admission |
| 3 | Occupational Health Services |
| 3 | Nursing Homes |
| 3 | Newcastle disease virus |
| 3 | Newcastle Disease |
| 3 | Neutralization Tests |
| 3 | Neoplasms |
| 3 | Mutation, Missense |
| 3 | Multivariate Analysis |
| 3 | Motivation |
| 3 | Models, Economic |
| 3 | Models, Econometric |
| 3 | Meat |
| 3 | Measles |
| 3 | Measles Vaccine |
| 3 | Mandatory Reporting |
| 3 | Mandatory Programs |
| 3 | Liver Transplantation |
| 3 | Length of Stay |
| 3 | Internal Medicine |
| 3 | Inpatients |
| 3 | Influenza Pandemic, 1918-1919 |
| 3 | Influenza A Virus, H3N8 Subtype |
| 3 | Influenza A Virus, H2N2 Subtype |
| 3 | Immunosuppressive Agents |
| 3 | Immunogenicity, Vaccine |
| 3 | Immunocompetence |
| 3 | Immune Sera |
| 3 | Humidity |
| 3 | History, 19th Century |
| 3 | Herpes Zoster |
| 3 | Hepatitis B |
| 3 | Health Services for the Aged |
| 3 | Health Services Needs and Demand |
| 3 | Health Planning Guidelines |
| 3 | Health Education |
| 3 | Government Programs |
| 3 | Genetic Drift |
| 3 | Frail Elderly |
| 3 | Feasibility Studies |
| 3 | Evolution, Molecular |
| 3 | Erythrocyte Transfusion |
| 3 | Epitopes |
| 3 | Epidemiologic Methods |
| 3 | Environmental Exposure |
| 3 | Disinfection |
| 3 | Disease Progression |
| 3 | Diabetes Mellitus |
| 3 | Denmark |
| 3 | Data Interpretation, Statistical |
| 3 | DNA, Viral |
| 3 | Czech Republic |
| 3 | Crohn Disease |
| 3 | Cough |
| 3 | Coronavirus Infections |
| 3 | Contact Tracing |
| 3 | Communication |
| 3 | Clinical Laboratory Techniques |
| 3 | Bronchitis |
| 3 | Blood Banks |
| 3 | Biomedical Research |
| 3 | Antirheumatic Agents |
| 3 | Anti-Infective Agents |
| 3 | Animal Welfare |
| 3 | Animal Migration |
| 3 | Analysis of Variance |
| 3 | Air Pollution |
| 3 | Adenovirus Infections, Human |
| 2 | Vaccines, Virosome |
| 2 | Vaccines, Conjugate |
| 2 | Uterine Cervical Neoplasms |
| 2 | Typhoid Fever |
| 2 | Trust |
| 2 | Treatment Refusal |
| 2 | Transients and Migrants |
| 2 | Time |
| 2 | Sus scrofa |
| 2 | Superinfection |
| 2 | Statistics as Topic |
| 2 | Specimen Handling |
| 2 | Specific Pathogen-Free Organisms |
| 2 | Software |
| 2 | Socioeconomic Factors |
| 2 | Social Responsibility |
| 2 | Social Class |
| 2 | Slovenia |
| 2 | Single-Blind Method |
| 2 | Severe Acute Respiratory Syndrome |
| 2 | Sequence Analysis, RNA |
| 2 | Schools |
| 2 | Sampling Studies |
| 2 | Salmonella Infections |
| 2 | Rubella Vaccine |
| 2 | Rhinovirus |
| 2 | Respiratory System |
| 2 | Reimbursement Mechanisms |
| 2 | ROC Curve |
| 2 | Quarantine |
| 2 | Pulmonary Medicine |
| 2 | Pulmonary Disease, Chronic Obstructive |
| 2 | Psoriasis |
| 2 | Psittacosis |
| 2 | Proportional Hazards Models |
| 2 | Program Evaluation |
| 2 | Probability |
| 2 | Preventive Medicine |
| 2 | Preventive Health Services |
| 2 | Pregnant Women |
| 2 | Predictive Value of Tests |
| 2 | Population Dynamics |
| 2 | Polysorbates |
| 2 | Polymorphism, Genetic |
| 2 | Poland |
| 2 | Point-of-Care Systems |
| 2 | Point Mutation |
| 2 | Pneumonia, Mycoplasma |
| 2 | Plant Oils |
| 2 | Phytotherapy |
| 2 | Physician Assistants |
| 2 | Perception |
| 2 | Patient Care Team |
| 2 | Parvoviridae Infections |
| 2 | Paratyphoid Fever |
| 2 | Parasitic Diseases |
| 2 | Paramyxoviridae |
| 2 | Otitis Media |
| 2 | Occupations |
| 2 | Occupational Medicine |
| 2 | Occupational Health |
| 2 | Nucleic Acid Amplification Techniques |
| 2 | Nose |
| 2 | Norway |
| 2 | North Sea |
| 2 | Nonlinear Dynamics |
| 2 | Needs Assessment |
| 2 | Nasal Cavity |
| 2 | Myocardium |
| 2 | Mustelidae |
| 2 | Multiple Sclerosis, Relapsing-Remitting |
| 2 | Molecular Structure |
| 2 | Mobile Health Units |
| 2 | Military Personnel |
| 2 | Meteorological Concepts |
| 2 | Meningococcal Vaccines |
| 2 | Meningococcal Infections |
| 2 | Medicine, Traditional |
| 2 | Medical Oncology |
| 2 | Mathematical Computing |
| 2 | Mass Screening |
| 2 | Malaria |
| 2 | Lymphocyte Activation |
| 2 | Longitudinal Studies |
| 2 | Liver |
| 2 | Laboratories |
