The effects of a potential national campaign and a VEI

type vaccine on an HIV-1 infected homosexually active

population José Alvarado Oscar Estrada University of Puerto Rico, Cayey Campus Universidad Autónoma de Ciudad Juárez

Emily Kajita Nadia Monrose Harvey Mudd College University of the Virgin Islands

Introduction

•Some researchers have discovered vaccines which prevent the transmission of the virus. These vaccines, called Vaccine Efficacy for Infectiousness (VEI), are still being tested.

•Studies suggest that there are early symptoms of HIV.

•A national campaign promoting HIV testing can be comparatively much less expensive than the development of a vaccine and possibly just as effective for the overall population in reducing the epidemic.

•The hypothetical national campaign we introduce targets those who exhibit early symptoms to test for HIV.

•How does a VEI type vaccine together with a national education campaign affect the HIV epidemic?

The Model

Assumptions

•We assume a homogeneous homosexually active male population.

•An individual spends the same period of time in each state.

•Only individuals in the first state are screened.

•An individual who has not developed full-blown AIDS is unaware of what stage of infection he is in.

•We assume that every contact between any non-vaccinated infected and a susceptible results in transmission of the virus.

•We assume that once the individual has been detected, he refrains from sexual activity.

•Vaccination is random.

•Vaccination does not affect the transition from one infectious state to another.

Assumptions (continued)

3

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NS

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2

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Methodology

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CBA 23

0 1 2 3 4 5 6 7 8 9 100

100

200

300

400

500

600

700

800

900

1000

Time (years)

Sus

cept

ible

vac

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dS/dt=-wSS(t)=S(o)*exp(-wt)

Prob

abili

ty o

f esc

apin

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ing

Conclusions

•The efficacy of the vaccine has a greater impact on the epidemic than the efficacy of the campaign.

•Increasing the efficacy of the vaccine results in an increase in the probability of extinction of the epidemic, as expected.

•In order to drive the epidemic to extinction, the minimum efficacy of the vaccine must be approximately 95%.

•Increasing the efficacy of the campaign up to 66.3% results in an increase in the probability of extinction, above which the probability of extinction decreases.

•Although a VEI vaccine with less than 95% efficacy will not drive the epidemic to extinction, it can reduce the prevalence of the epidemic, especially if coupled with a national campaign.

Potential Extensions

•An individual progresses from one state to the next at different rates.

•A heterosexually active population can be used.

•The waning effect of the VEI type vaccine could be different for each state.

•Analyze how the contact rate influences the dynamics of the model.

Acknowledgments

This research was made possible by the following institutions and grants: National Science Foundation (NSF Grant DMS-9977919 8/99-8/09); National Security Agency (NSA Grant MDA-904-00-1-0006 11/99-11/00); Presidential Faculty Fellowship Award(NSF Grant DEB 925370); Presidential Mentoring Award (NSF Grant HRD 9724850) to Carlos Castillo-Chávez; Cornell University-Office of the Provost; and Intel Technology for Education 2000 Equipment Grant.

We would like to thank Dr. Carlos M. Hernández and special thanks to Dr. Carlos Castillo-Chávez for their invaluable assistance.