# Presentation: 688179

## 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*

## Standard Thinking: The Critical Vaccination Threshold, pc

**Eradication**

**0**

**0.2**

**0.4**

**0.6**

**0.8**

**1**

**0**

**2**

**4**

**6**

**8**

**10**

**12**

**14**

**16**

**18**

**20**

**Basic Reproductive Rate, R****0**

**Persistence**

***Measles***

***Rubella***

**Critical proportion, p****c**

***Hib***

*Department of Infectious Disease Epidemiology, Imperial College*

** ****Efficacy of STD vaccines likely less than childhood vaccines.**
** ****Delivery of vaccines against STDs controversial?**
** ****Platform for vaccine targeting and delivery.**

## Efficacy v

**0**

**0.4**

**0.8**

**0**

**0.2**

**0.4**

**0.6**

**0.8**

**1**

**0**

**0.1**

**0.2**

**0.3**

**0.4**

**0.5**

**0.6**

**0.7**

**0.8**

**Prevalence**

**Take**

**Degree**

***Impact of vaccination sub elimination - simple theory***
**Meaning of efficacy vital.**

_***Degree***_** – protected from a fraction of challenges**

_***Take***_** – fraction protected from all challenges**

_**Efficacy **__***v***_

*Department of Infectious Disease Epidemiology, Imperial College*

## The impact of behavioural reversals on endemic 

***The impact of behavioural reversals on endemic***** **

**prevalence - 50% vaccine efficacy**
**Increased risk increases the basic reproductive number**

**0**

**0.2**

**0.4**

**0.6**

**0.8**

**1**

**0**

**100**

**200**

**300**

**400**

**500**

**Percentage increase in risk behaviour**

**Equilibrium prevalence**

**Degree**

**Take**

*Department of Infectious Disease Epidemiology, Imperial College*

## Cohort vaccination - endemic HIV prevalence

***Cohort vaccination - endemic HIV prevalence***
**‘****Take’ type efficacy reduces susceptibility:**

**0**

**0.1**

**0.2**

**0.3**

**0**

**0.1**

**0.2**

**0.3**

**0.4**

**0.5**

**0.6**

**0.7**

**0.8**

**Proportion of sexually active adults infected **
**30 years after introducing vaccine**

*Department of Infectious Disease Epidemiology, Imperial College*

## Reducing the effective and basic reproductive rate

***Reducing the effective and basic reproductive rate***

**0**

**20**

**40**

**60**

**80**

**100**

**Percent**

**Reduced Transmission**

**probability**

**Effectively vaccinated**

**Endemic Prevalence (%)**

*Department of Infectious Disease Epidemiology, Imperial College*

## 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*

## Incidence ICC per 100,000

**Age**

** ****All HR HPV**

** ****All HR HPV; screening**

** ****HR HPV w/o 16, 18**

** ****HR HPV w/o 16, 18; screening**

**20**

**40**

**60**

**80**

**0**

**.0001**

**.0002**

**.0003**

**.0004**

*Department of Infectious Disease Epidemiology, Imperial College*

## Department of Infectious Disease Epidemiology, Imperial College

*Department of Infectious Disease Epidemiology, Imperial College*

## 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**