Emerging, evolving, and established infectious diseases and interventions

Abstract

Planning, implementing, and evaluating interventions against infectious diseases depend on the nature of the infectious disease; the availability of intervention measures; and logistical, economic, and political constraints. Infectious diseases and vaccine- or drug-based interventions can be loosely categorized by the degree to which the infectious disease and the intervention are well established. Pertussis, polio, and measles are three examples of long-known infectious diseases for which global vaccination has dramatically reduced the public health burden. Pertussis vaccination was introduced in the 1940s, polio vaccination in the 1950s, and measles vaccination in the 1960s, nearly eliminating these diseases in many places.

Figure 1

A mathematical model of cholera transmission was used to estimate the effectiveness (number of cases averted) and cost-effectiveness in disability averted life years (DALYs) when a given fraction of the population is vaccinated. The model predicts that the fraction of cases averted by mass vaccination (black solid line) exceeds the estimates when only direct protection is assumed (red dashed line). The black dots indicate levels of protection observed in a cholera vaccine trial [21]. In addition, the relationship between vaccine coverage and effectiveness is not linear when assuming overall protection, unlike direct protection [7].

Figure 2

Mass vaccination is more cost-effective when overall protection is considered compared to calculations that only account for direct protection. According to WHO convention, the ratio of program cost to DALYs Averted in a cost-effectiveness analysis is classified by the per capita national gross domestic product (GDP) of the country of interest: less than GDP/capita classifies an intervention as very cost-effective; between 1 and 3 times GDP/capita is cost-effective; and more than 3 times the GDP/capita is cost-ineffective [7, 22].