The Population Process Model

The mathematical framework underlying SMART Vaccines was developed in Phase I and has been enhanced to result in the present software, a comprehensive explanation about the model is provided in the second and third chapters of the Phase I report, Ranking Vaccines: A Prioritization Framework (IOM, 2012). The SMART Vaccine 1.0 population process model uses a cohort component method to project populations forward at yearly intervals (Preston et al., 2001) The yearly aging process is simulated for both a baseline population with no vaccine (i.e., the control) and a test population with either (1) the vaccine in approximated steady state delivery or (2) the vaccine having been newly introduced, and the two populations are compared. Table A-1, provides a comprehensive description of these three population vaccine conditions. It is through comparing a vaccinated population to the baseline that the various health and economic measures are estimated over the appropriate time-scale.

The model assumes a constant number of infants entering the population each year, with the number being given by the number of infants (i.e.,

TABLE A-1
Population Comparison in the SMART Vaccines Process Model

Population Description
Baseline The baseline population is the reference for comparison. Vaccines not yet developed and those used in SMART Vaccines 1.0 have a baseline population in which no vaccine has been used. However, in cases where a vaccine does exist, the baseline population may reflect the current vaccination state as reference against which to compare hypothetical newly developed vaccines for the same disease that have different (i.e., more desirable) characteristics.
Vaccine in approximated steady state delivery In a population in which the vaccine is being administered under the steady state approximation it is assumed that individuals of all ages have had the opportunity (i.e., accounting for coverage) to receive the vaccine. For example, in the case of a vaccine that solely targets infants, individuals of all ages are assumed to have had the opportunity for vaccination. Achieving steady state for an infant vaccination would require many years, unlike the case with a vaccine designed for delivery to all ages.
Vaccine first being introduced In the case of a vaccine first being introduced into a population it is assumed that the vaccine was delivered solely to the target population (i.e., accounting for coverage) at model initialization. No other members of the population will have had the opportunity to have received the vaccine.


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