Seasonal influenza vaccination
Authors: Hanquet Germaine , Jonckheer Pascale , Vlayen Joan , Vrijens France , Thiry Nancy , Beutels Philippe 
Published: January 2025

Table of contents -- LIST OF FIGURES 5 -- LIST OF TABLES 6 -- GLOSSARY 9 -- 1 INTRODUCTION 10 -- 1.1 INFLUENZA DISEASE 10 -- 1.2 VACCINES FOR SEASONAL INFLUENZA 10 -- 1.3 SEASONAL INFLUENZA VACCINATION IN BELGIUM 12 -- 2 RESEARCH QUESTIONS13 -- 3 METHODS 14 -- 3.1 TARGET GROUPS AND VACCINATION SCENARIOS 14 -- 3.2 DENOMINATORS 15 -- 3.3 PARAMETERS FOR INFLUENZA SEASONS 15 -- 3.3.1 Influenza seasons and viral activity seasons 15 -- 3.3.2 Matching and season intensity 16 -- 3.4 MODEL 16 -- 3.5 PARAMETERS FOR INFLUENZA OUTCOMES 17 -- 3.5.1 Overall methodological approach 18 -- 3.5.2 Outpatient cases of ILI and confirmed influenza cases 19 -- 3.5.3 Inpatient cases of influenza and/or pneumonia 20 -- 3.5.4 Deaths from influenza and/or pneumonia 20 -- 3.6 PARAMETERS FOR VACCINE EFFECTIVENESS 21 -- 3.7 SENSITIVITY ANALYSIS 22 -- 3.8 ASSUMPTIONS USED 23 -- 4 DETERMINATION OF PARAMETERS 24 -- 4.1 DENOMINATORS 24 -- 4.2 INFLUENZA SEASONS 24 -- 4.3 INFLUENZA BURDEN BY INFLUENZA SEASON 25 -- 4.3.1 Outpatient cases of ILI and confirmed influenza 25 -- 4.3.2 Admissions for influenza and pneumonia 28 -- 4.3.3 Deaths from influenza and pneumonia 33 -- 4.4 INFLUENZA BURDEN DURING VIRAL ACTIVITY SEASONS36 -- 4.5 INFLUENZA VACCINE EFFECTIVENESS (IVE) 37 -- 4.5.1 IVE parameters in healthy adults (15-64 years) 38 -- 4.5.2 IVE parameters in elderly (65 years and above) 40 -- 4.5.3 IVE parameters in 1-64 years with co-morbidities 41 -- 4.5.4 IVE parameters in HCWs 42 -- 4.5.5 IVE parameters in pregnant women 42 -- 5 IMPACT CALCULATIONS 43 -- 5.1 VACCINE NEEDS BY SCENARIO 43 -- 5.2 IMPACT OF EACH VACCINATION SCENARIO IN AN INFLUENZA SEASON 44 -- 5.2.1 Vaccination of persons 1-64 years old with co-morbidities 44 -- 5.2.2 Vaccination of the elderly 65-74 years of age 45 -- 5.2.3 Vaccination of the elderly &#8805;75 years of age 47 -- 5.2.4 Vaccination of healthy adults 50-64 years 47 -- 5.2.5 Vaccination of HCW 49 -- 5.2.6 Vaccination of pregnant women49 -- 5.2.7 Not vaccinating healthy adults 15-49 years 50 -- 5.3 IMPACT OF EACH VACCINATION SCENARIO IN AN ACTIVITY SEASON 51 -- 5.3.1 Vaccination of persons 1-64 years with co-morbidities 51 -- 5.3.2 Vaccination of the elderly 65-74 years of age 51 -- 5.3.3 Vaccination of the elderly &#8805;75 years of age 51 -- 5.3.4 Vaccination of healthy adults 50-64 years 51 -- 5.3.5 Vaccination in HCW 51 -- 5.3.6 Vaccination of pregnant women51 -- 5.3.7 Not vaccinating healthy adults 15-49 years 51 -- 5.4 SUMMARY OF IMPACT BY VACCINATION SCENARIO 51 -- 5.5 UNCERTAINTY AND SENSITIVITY ANALYSES 56 -- 6 DISCUSSION 58 -- 7 CONCLUSIONS ON PRIORITY SETTING 61 -- 8 APPENDIX 1: DATA SOURCES AND METHODS TO ESTIMATE MEDICAL -- BURDEN AND UPTAKE 62 -- 8.1 CURRENT VACCINE UPTAKE 62 -- 8.2 INFLUENZA SEASONS 62 -- 8.3 POPULATION FIGURES 63 -- 8.4 OUTPATIENT CASES OF INFLUENZA-LIKE ILLNESS AND INFLUENZA 64 -- 8.4.1 ILI cases reported to the IPH Sentinel Network of GPs 64 -- 8.4.2 ILI laboratory results from the IPH National Influenza Centre 64 -- 8.4.3 Estimation of total ILI and influenza cases 65 -- 8.5 HOSPITAL ADMISSIONS FOR INFLUENZA AND PNEUMONIA 66 -- 8.5.1 Source of data 66 -- 8.5.2 Estimation of admission parameters 67 -- 8.6 DEATHS FROM INFLUENZA AND PNEUMONIA 68 -- 8.6.1 Cause-specific deaths from Flanders, Wallonia and Brussels 68 -- 8.6.2 In hospital deaths from MCD database 68 -- 8.6.3 Estimation of mortality parameters 69 -- 8.7 TARGET GROUP FOR SEASONAL INFLUENZA VACCINATION IN BELGIUM 69 -- 9 APPENDIX 2: RESULTS ON INFLUENZA DISEASE BURDEN 70 -- 9.1 INFLUENZA ACTIVITY SEASONS 70 -- 9.2 POPULATION FIGURES 70 -- 9.3 ILI AND INFLUENZA CASES BY INFLUENZA SEASON 71 -- 9.3.1 Cases reported and swabbed by the network 71 -- 9.3.2 ILI in the Belgian population 72 -- 9.3.3 Influenza in the Belgian population 73 -- 9.4 ADMISSIONS FOR INFLUENZA AND PNEUMONIA BY INFLUENZA SEASON 76 -- 9.4.1 Admissions by age group 76 -- 9.4.2 Admission in healthy adults aged 15-75 years 81 -- 9.4.3 Admissions in persons with co-morbidities 81 -- 9.4.4 Admissions in pregnant women 83 -- 9.4.5 Admissions in HCW 85 -- 9.5 DEATHS FROM INFLUENZA AND PNEUMONIA BY INFLUENZA SEASON 85 -- 9.5.1 Deaths by age group 85 -- 9.5.2 Deaths by co-morbidity status (<75 years) 88 -- 9.5.3 Deaths in pregnancy 90 -- 9.5.4 Deaths in HCW 90 -- 9.6 INFLUENZA BURDEN BY SEASON OF VIRAL ACTIVITY90 -- 9.7 VACCINE UPTAKE 92 -- 10 APPENDIX 3: LITERATURE REVIEW ON BURDEN OF INFLUENZA IN -- SPECIFIC TARGET GROUPS 93 -- 10.1 METHODS 93 -- 10.2 ADULTS WITH UNDERLYING CONDITIONS 93 -- 10.2.1 Outpatient influenza in adults with underlying conditions 93 -- 10.2.2 Hospitalizations in adults with underlying conditions 94 -- 10.2.3 Mortality in adults with underlying conditions 95 -- 10.3 ELDERLY WITH UNDERLYING CONDITIONS 96 -- 10.3.1 Outpatient influenza/ILI in elderly with underlying conditions 96 -- 10.3.2 Hospitalization in elderly with underlying conditions 96 -- 10.3.3 Mortality in elderly with underlying conditions 96 -- 10.4 CHILDREN WITH UNDERLYING CONDITIONS 97 -- 10.4.1 Outpatient influenza/ILI in children with underlying conditions 97 -- 10.4.2 Hospitalization in children with underlying conditions 98 -- 10.4.3 Mortality in children with underlying conditions 99 -- 10.5 PREGNANT WOMEN 100 -- 10.5.1 Outpatient influenza/ILI in pregnant women 100 -- 10.5.2 Hospitalisation in pregnant women 100 -- 10.5.3 Mortality in pregnant women 101 -- 10.5.4 Outcome of the foetus 101 -- 10.6 HEALTH CARE WORKERS 102 -- 10.6.1 Definition of health care workers 102 -- 10.6.2 Outpatient influenza/ILI in health care workers (HCW) 102 -- 10.6.3 Mortality in health care workers 102 -- 10.6.4 Transmission in vulnerable patients 103 -- 11 APPENDIX 4: SELECTION OF PARAMETERS ON INFLUENZA VACCINE -- EFFICACY AND EFFECTIVENESS 104 -- 11.1 METHODS 104 -- 11.1.1 Inclusion criteria for IVE studies 104 -- 11.1.2 Data analysis 104 -- 11.2 IVE PARAMETERS 105 -- 11.2.1 Healthy adults 106 -- 11.2.2 Patients 15-64 years with co-morbidities 109 -- 11.2.3 Elderly (65 years and above) 109 -- 11.2.4 Pregnant women and infants 114 -- 11.2.5 Health care workers 115 -- 11.3 ADDITIONAL DATA VACCINE EFFECTIVENESS/EFFICACY FOR OUTCOME ILI 116 -- 12 APPENDIX 5: LITTERATURE REVIEW ON EFFICACY AND EFFECTIVENESS -- OF INFLUENZA VACCINATION117 -- 12.1 SEARCH STRATEGY 117 -- 12.1.1 Research question 117 -- 12.1.2 Searched databases 117 -- 12.1.3 Search strings and limits 118 -- 12.1.4 Inclusion criteria 118 -- 12.1.5 Quality appraisal and data extraction 118 -- 12.2 HEALTH CARE WORKERS 119 -- 12.2.1 Indirect effect on patients 119 -- 12.2.2 Direct effect on HCW 119 -- 12.3 PERSONS AT HIGH RISK OF INFLUENZA-RELATED COMPLICATIONS120 -- 12.3.1 Chronic respiratory diseases 120 -- 12.3.2 Diabetes 120 -- 12.3.3 Cardiovascular disease 120 -- 12.3.4 Other high-risk populations 120 -- 12.3.5 Patients with any co-morbidities 121 -- 12.4 PREGNANT WOMEN 121 -- 12.5 PERSONS AGED 65 OR MORE122 -- 12.5.1 Systematic reviews 122 -- 12.5.2 Primary studies 123 -- 12.6 HEALTHY ADULTS AGED 18-64 YEARS 124 -- 12.7 SEARCH SYNTAXES 125 -- 12.7.1 OVID Medline 125 -- 12.7.2 EMBASE 128 -- 12.7.3 Cochrane database of systematic reviews and DARE (through Cochrane library) 130 -- 12.7.4 CENTRAL (through Cochrane library) 130 -- 13 APPENDIX 6: DISTRIBUTION OF INPUT PARAMETERS FOR AND RESULTS -- FROM THE UNCERTAINTY ANALYSIS 131 -- 13.1 DISTRIBUTION OF INPUT PARAMETERS 131 -- 13.2 RESULTS OF THE MONTECARLO SIMULATIONS 133 -- 14 REFERENCES 134