Vaccines: A success story with failures. Aims of vaccination

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1 Vaccines: A success story with failures Ursula Wiedermann Institute of Specific Prophylaxis and Tropical Medicine, Medical University Vienna Aims of vaccination Individual protection! (protection against infection/disease) Elimination (reduction of infection in certain geographic area; protection of re-emergering diseases) Eradication (premanent worldwide elimination of pathogen) High vaccination coverage Collective protection Herd immunity; reduction of transmission Reduction of incidence of disease prevention of epidemics 1

2 Benefit-Risk, Benefit-Cost Ratio Public health issues of vaccination programs Benefit-Risk Ratio (important for individual consideration): Evaluation of the risk of disease and the risk of vaccination with respect to the same risk parameter (death, sequelae) within a certain time interval: For all existing vaccines the calculation of the benefit/risk ratio is positive Benefit-Cost Estimation (for implementation of vaccine programs): is calculated to document social-economic savings through high vaccination coverage: the benefit-cost ratio is positive for diseases with high incidence and high morbidity; For diseases with high individual risk for morbidity/mortality but low incidence this calculation is not always positive Positive benefit-cost ratio: Reduction of therapy costs Reduction of hospitalisation rates Reduction of prevalence and incidence Number of gained life years Number of gained working days High vaccination coverage Collective protection Herd immunity; reduction of transmission Reduction of incidence of disease prevention of epidemics Ehret J, Vaccine

3 Definition of efficacy versus effectiveness Efficacy : Measures the protective effect of a vaccine with respect to a defined endpoint and selected study population = ideal study situation (non real lifes situation ) Effectiveness Measures the protective effect of a vaccine under real life conditions non selected population, non controlled (for age, disease, preexisting immunity etc - direct, indirect, total, overal effects) Development of human vaccines 3

4 Impact of vaccination on epidemiology of infections Cost benefit is the sum of direct and indirect effects 4

5 Indirect effects - Herd immunity = Protective value of a vaccine is due to: Direct protective effect of a vaccine Number of vaccinated people Leads to: Protection of unvaccinated Improved protection of vaccinated Improvemet of cost-benefit ratio Herd immunity/protection Results from: Reduction of pathogen transmission in a population that is protected to a certain percentage via vaccination ( herd protection ): Only possible with human to human transmission; Possible with live or inactivated vaccines 5

6 Erreger-Transmission von Mensch zu Mensch Transmissability = Übertragungskapazität eines Erregers wird durch die Basisreproduktionszahl (R 0 ) definiert: = Anzahl an Personen in einer ungeschützten Population, die durch 1 Infizierten angesteckt werden Hängt ab von: Biologischen Eigenschaften des Erregers (Pathogenität, Virulenz) Häufigkeit des Erregerkontakts und Art des Kontakts Umweltbedingungen (Temperatur, Kontaktbedingungen wie Schule, Altersheim, Haushalt, Immunstatus, etc) Herd immunity threshold = Mindestdurchimpfungsrate die zur Verhinderung einer Epidemie ausreicht (unter der Annahme, dass Vakzine 100% wirksam) Epidemic Prevention of epidemic R n= Netto Reproductions number; 1 Vaccination rate: 75% 6

7 Infektion Basisreproduktionszahl (R 0 ) Diphtherie Durchimpfungsrate (%)* Influenza 1, Masern Mumps Pertussis Polio Röteln Varizellen *Assuming that the vaccine efficacy is 100% if it < 100%, vaccination coverage needs to be higher Correlates of vaccine-induced immunity 7

8 Definition of correlates of protection 8

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13 Safety and acceptance 13

14 Adverse events following immunization Hypotonic, hyoresponsive episodes 14