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New vaccines mean new strategies: A theoretical exploration of the impact of HPV/HSV vaccines.

New vaccines mean new strategies: A theoretical exploration of the impact of HPV/HSV vaccines. Geoff Garnett Department of Infectious Disease Epidemiology, Imperial College, London. Department of Infectious Disease Epidemiology, Imperial College.

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New vaccines mean new strategies: A theoretical exploration of the impact of HPV/HSV vaccines.

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  1. New vaccines mean new strategies: A theoretical exploration of the impact of HPV/HSV vaccines. Geoff Garnett Department of Infectious Disease Epidemiology, Imperial College, London. Department of Infectious Disease Epidemiology, Imperial College

  2. Standard Thinking: The Critical Vaccination Threshold, pc 1 Eradication 0.8 Persistence 0.6 Critical proportion, pc Measles 0.4 Rubella Hib 0.2 0 0 2 4 6 8 10 12 14 16 18 20 Basic Reproductive Rate, R0 • Efficacy of STD vaccines likely less than childhood vaccines. • Delivery of vaccines against STDs controversial? • Platform for vaccine targeting and delivery. Department of Infectious Disease Epidemiology, Imperial College

  3. Impact of vaccination sub elimination - simple theory Meaning of efficacy vital. Efficacy v Degree – protected from a fraction of challenges Prevalence 0.8 0.7 0.6 Take – fraction protected from all challenges 0.5 0.4 0.3 0 0.2 0.4 0.1 Take 0 0.8 1 0.8 0.6 0.4 0.2 0 Degree Department of Infectious Disease Epidemiology, Imperial College

  4. The impact of behavioural reversals on endemic prevalence - 50% vaccine efficacy Increased risk increases the basic reproductive number 1 Degree 0.8 0.6 Equilibrium prevalence Take 0.4 0.2 0 0 100 200 300 400 500 Percentage increase in risk behaviour Department of Infectious Disease Epidemiology, Imperial College

  5. Cohort vaccination - endemic HIV prevalence ‘Take’ type efficacy reduces susceptibility: 0.3 0.2 Proportion of sexually active adults infected 30 years after introducing vaccine 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Proportion of each cohort effectively vaccinated Department of Infectious Disease Epidemiology, Imperial College

  6. 16 14 12 10 8 6 4 2 0 Reducing the effective and basic reproductive rate Reduced Transmission probability Effectively vaccinated Endemic Prevalence (%) 0 20 40 60 80 100 Percent Department of Infectious Disease Epidemiology, Imperial College

  7. Risks of release from competition of more pathogenic strains? • Requires cross immunity • Requires that cross immunity not generated by vaccine • Requires that frequency dependent selection is limiting incidence of infection • What is additional influence of vaccination interacting with screening? • What is the impact of competing hazards in success of an HPV vaccine? Department of Infectious Disease Epidemiology, Imperial College

  8. All HR HPV All HR HPV; screening HR HPV w/o 16, 18 HR HPV w/o 16, 18; screening .0004 .0003 Incidence ICC per 100,000 .0002 .0001 0 20 40 60 80 Age Department of Infectious Disease Epidemiology, Imperial College

  9. 100 50 % reduction in CIS 0 0 50 100 % reduction in hazard of HPV infection Department of Infectious Disease Epidemiology, Imperial College

  10. Conclusions • STD vaccines with ‘limited’ efficacy could provide powerful intervention tools. • Impact of an HSV vaccine depends upon impact of viral shedding. • Targeting unlikely to be useful for vaccines against viral STDs. • HPV vaccination strategy needs to include ongoing effective screening. • Little risk of competitive release of virulent HPV types

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