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Direct, Indirect, Total and Population Vaccination Effectiveness in Pandemic influenza Vaccination

Xu, Songli (2012)
Master's Thesis (34 pages)
Committee Chair / Thesis Adviser: Haber, Michael J
Committee Members: Nizam, Azhar
Research Fields: Health Sciences, Epidemiology
Partnering Agencies: Does not apply (no collaborating organization)
Keywords: influenza vaccination
Program: Rollins School of Public Health, Biostatistics and Bioinformatics (Biostatistics)
Permanent url: http://pid.emory.edu/ark:/25593/br24m

Abstract


Most vaccination effectiveness studies focus on the direct vaccination effectiveness
(VEd), defined as one minus the ratio of attack rates in vaccinated and unvaccinated
persons, and pay little attention to the indirect (VEi) and population (VEpop)
effectiveness, which can be interpreted as proportion of cases prevented by
vaccination. Here, we use a stochastic simulation model to estimate direct, indirect,
total and population vaccination effectiveness using data from the 1957/1958
influenza pandemic To estimate VEpop, which is unknown, from VEd and the
vaccination fraction, which are known, linear regression modeling and estimation
under the Susceptible-Infected-Removed (SIR) model were performed. From
simulation results, we found the VEpop is usually higher, and in many cases much
higher, than the VEd. In prediction studies, results from linear regression models
showed that the estimates of population effectiveness were close to the simulated
results when vaccination fractions were fixed, and that the estimation of population
effectiveness can best approximate the simulated values when vaccine efficacy (VEs)
is fixed and equals to 0.4. Our results also show that estimation of VEpop based on
the SIR model provides a good approximation t0 the true population effectiveness
even though, in the real world, the basic SIR model assumptions that the population
is homogeneous and mixing is random are violated. We conclude that, due to the
indirect vaccination effects, the VEpop is usually higher than the VEd. In addition,
linear regression and SIR models can be applied to estimate VEpop.


Direct, Indirect, Total and Population Vaccination Effectiveness in
Pandemic influenza Vaccination


B.S. Henan Normal University, China, 1991
M.S. Zhengzhou University School of Medicine, China, 1998
Ph.D. Fudan University School of Medicine, China, 2001
Thesis Committee Chair: Michael J Haber, Ph.D.
A thesis submitted to the Faculty of the
Rollins School of Public Health of Emory University
in partial fulfillment of the requirements for the degree of
Master of Public Health
2012



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