Identifying Future Disease Hot Spots

Recent high-profile outbreaks, such as those caused by the Ebola and Zika viruses, have illustrated the transnational nature of infectious diseases and the need for coordinated actions to curtail the outbreaks. Countries that are most vulnerable to such outbreaks might be higher priorities for technical and funding support. To help identify these countries, we created the Infectious Disease Vulnerability Index. This index was designed as a tool for U.S. government and international agencies to provide a clearer understanding of countries' vulnerabilities to infectious disease and thereby to help inform decisionmaking and actions about taking preemptive steps to mitigate the effects of potential widespread outbreaks.

We employed a rigorous methodology to identify the countries most vulnerable to disease outbreaks. This study builds on a proof of concept we published in the context of the Ebola outbreak (Gelfeld et al., 2015). We conducted a comprehensive review of relevant literature to identify factors influencing vulnerability to infectious disease outbreaks, which we organized into seven broad domains: demographic, health care, public health, disease dynamics, political-domestic, political-international, and economic. Using widely available data (e.g., from the World Bank, the World Health Organization, and other international organizations), we created a tool to generate an index that allows us to identify and rank potentially vulnerable countries. The tool is built to enable user-adjusted weights for individual parameters and for domains as a whole. We drew from both the rigorous literature review and our extensive experiences in epidemiology, global health, and the social sciences to create a baseline set of weights and outputs and then carried out sensitivity analyses by systematically varying the weights across all domains.

Key findings from our assessment include a heat map reflecting normed scores for all countries worldwide with regard to their vulnerability to infectious disease outbreaks (Figure 1) and a ranked list of countries based on their vulnerability. Unsurprisingly, 22 of the 25 most-vulnerable countries are in the Africa region (within the Department of Defense's U.S. Africa Command area of responsibility); the other three are Afghanistan and Yemen (within U.S. Central Command) and Haiti (within U.S. Southern Command). Sensitivity testing first removed all weighting (i.e., all weights set to 1.0) and then systematically zeroed out (i.e., weight set to zero), doubled and tripled each domain weight. This testing indicated that most of the top-25 (i.e., most-vulnerable) countries remained within that range, albeit at different rankings, suggesting that the tool is highly robust to variability of parameter values from the perspective of the ranking country's vulnerability to infectious disease outbreaks. Of particular concern are conflict-affected countries, such as Somalia (ranked 1), Central African Republic (ranked 2), and South Sudan (ranked 4), all of which play host to a dangerous combination of political instability and compromised health systems.

To support our interpretation of the findings, we compared health outcomes in seven countries affected by Ebola in 2014. This comparison suggested that a high vulnerability score alone does not necessarily condemn a country to poor outcomes with regard to disease outbreaks.

We would encourage policymakers to focus on the most-vulnerable countries, with an eye toward a potential “disease belt” in the Sahel region, which emerged from the data. Of note, the vulnerability score for several countries was better than what would have been predicted on the basis of economic indicators alone. This suggests that low-income countries can overcome economic challenges and become more resilient to public health challenges.

Our aim in designing this algorithm is to provide a useful tool for U.S. federal agencies and national and international health planners worldwide to help identify and raise awareness of those countries that might be most vulnerable to infectious disease outbreaks. The algorithm can be used to guide strategic planning and programming to address vulnerabilities in health systems or other critical sectors and hone in on cases of critical geographic, demographic, or regional importance. This tool highlights the connections between economic development, political stability, and disease vulnerability. With this information in mind, the Department of Defense, the Department of Health and Human Services (e.g., through the Centers for Disease Control and Prevention), the U.S. Agency for International Development, and the international community more broadly can take targeted actions to shore up weak health systems and help countries prepare for future infectious disease outbreaks with the potential for transnational spread. Such agencies should continue or ramp up programming to strengthen public health systems (e.g., disease surveillance, laboratory testing, outbreak detection, rapid response reams for investigation and disease-control measures), as well as medical care systems (e.g., professional training and certification, clinic and hospital care). Aid organizations, such as the U.S. Agency for International Development, should also continue to promote economic development and efforts to strengthen governance. For example, better governance through democracy-promotion and anticorruption programs may lead to less vulnerability as states improve the coordination, communication, and infrastructure systems that help to combat infectious disease transmission. Finally, exercises, including tabletop exercises, can be used to help countries better understand actions and actors, and the coordination needed among them, to best prepare systems to respond effectively to a disease threat that arises. With the multitude of disease threats that exist and the expanded opportunities for transmission in an increasingly globalized world, it is important to act now to better ensure that countries around the world, and especially the most-vulnerable countries, develop the enduring capabilities they need to effectively prevent, detect, and respond to disease threats before they get out of hand.