Global Health Institute

Sir Isaac Newton’s law of universal gravitation teaches us more than just how two masses attract each other from a distance. His famous equation relates the gravitational force between two objects to their respective masses and the distance separating the objects: 

F = G m1m2 

r2 

Interestingly, an essentially identical equation may be constructed that is capable of approximating migration flows between two locations, but this time as a function of population sizes (or even other measures) and distance separating the two locations. Generally, the equation below is referred to as a gravity model: 

Mij = G PiαPjβ 

rijγ 

where Mij represents the migrant population, Piα represents the population of the origin location (i), Pjβ represents the population of the destination location (j), and rijγ represents the distance between the two locations. G is just a proportionality constant for scaling purposes. α,β and γ are parameters usually estimated from data. 

My work this semester focused on estimating vaccine stockpile quantities for Nipah virus, a zoonotic virus (often transmitted by bats to humans) prevalent in India and Bangladesh. Estimating migration flow is of particular importance in modeling Nipah virus as it dictates how a disease may spread from location to location, via human travel. In turn, this will determine how and where vaccine stockpiles should be allotted. 

Often, data availability can be a barrier to research, since what data are available play a crucial role in what questions can be posed and answered. Thus, it is often necessary to create models that can closely approximate the unavailable data, based on a series of reasonable assumptions. In my case, because data on migration in India and Bangladesh are extremely scarce, a gravity model proved to be useful in providing estimates of population migration at the district level. I had data on district population and distances between districts, but needed to find values for the exponents in the model: α,β,γ. Briefly, the modeling process proceeded with reviewing travel and migration literature to understand how to properly parameterize the gravity model. After coding the model in Python, I tested various reported exponent values and plotted the results. I also attempted to validate my migration population data with summary-level data on migration in India. This served as a reality check to make sure the results were reasonable compared to what was expected. After some adjustments and scaling, the model output yielded promising results. 

In the larger scheme of the project, these migration estimates would feed into a larger model of Nipah virus transmission dynamics that would inform vaccine stockpile distribution. Vaccine stockpiling is an extremely important topic because it is one of our first lines of defense against the rampant spread of an epidemic or pandemic. It essentially puts the concept of prevention as the best form of a cure into practice. Additionally, estimates like these give policy-makers and vaccine manufacturers concrete, quantitative information on how to prepare for and prevent the spread of disease. 

Andrew Tiu (NHS `21) is an undergraduate studying human science and statistics. He is a student fellow with the Global Health Initiative.

As an intern at the Office of Global Affairs at the US Department of Health and Human Services this fall semester, I had the opportunity to help prepare HHS leadership to attend the 2019 G20 Health Ministers’ Meeting held in Okayama, Japan. The meeting was one of the eight ministerial gatherings that took place in addition to the G20 Summit. At these multilateral meetings member states work to advance ongoing collaboration and reaffirm shared commitments to address global health issues. The meetings also provide a platform for the member states to establish or further advance diplomatic relationships among themselves. The main themes of this year’s G20 Health Minister’s meeting was The Achievement of Universal Healthcare, Response to Aging Societies, and Health Risk Management and Health Security/Antimicrobial Resistance (AMR). 

At the conclusion of these meetings, member states often adopt a shared declaration. In the Okayama Declaration of the G20 Health Ministers, the member states agreed to various commitments in regards to The Achievement of Universal Healthcare such as “provide gender-responsive interventions to meet health needs of all and recognize immunizations is one of the most cost-effective health investments”. Other issues included in the declaration included promotion of health data and technologies, reform of health workforce programs, and cooperation with the private sector for financial sustainability of health systems. While there are often areas of disagreement on these issues, the high-level consensus of their importance by prominent member states an important signal that attention will be given to these issues. 

Similarly, in regards to the theme of Response to Aging Societies, the member states agreed on the importance of quality of life, utilization of health data, and addressing dementia-inclusive environments in society. The declaration also included action items such as encouraging OECD and other organizations to urge WHO to respond to its responsibility to prepare a Decade of Healthy Ageing 2020-2030 proposal and to treat aging as one of its priorities. Similarly, the declaration outlines more specific action items such as asking the member states to develop a national implementation plan in response to the WHA-endorsed Global Action Plan of the Public Health Response to Dementia 2017-2025 and focus their efforts on particular areas such as elderly labor market and early detection of dementia. The G20 consensus on the issue of aging is updated to address the evolving trends of demographic shifts and how the world’s public health system should prepare for the growing burden. 

The meeting is an important occasion where the health ministers and high-level health officials from various countries convene at one place. Health ministers and officials often hold bilateral meetings to reaffirm the importance of health cooperation, exchange each country’s health priorities, and explore future collaboration opportunities and ideas. On the sideline of the G20 Health Minister’s Meeting, for example, the HHS Deputy Secretary Eric Hargan represented the US and met with Health Minister Tawfig AlRabiah from Saudi Arabia to strengthen the two countries’ partnership on Global Health Security Agenda and the promotion of vaccines use. 

Another outcome was the signing of a Memorandum of Understanding (MoU) to establish a common line of goals and actions. Deputy Secretary Hargan also visited South Korea during this trip and signed a MoU between the U.S. Centers for Disease Control and Prevention (CDC) and the Korea CDC. The two CDCs agreed to collaborate on various public health issues including infectious disease outbreaks, anti-microbial resistance, and vaccine-preventable diseases. Specific action items such as information exchange and routine consultation are also listed to direct cooperative effort effectively.

Meetings like the G20 Health Ministers Meeting are important because they help prioritize public health issues among the member states and mobilize countries’ political leadership to address critical public health issues in the coming years. For readers who are interested in the high-level global health policy and hope to be informed, a quick and easy way is to follow the chief US health officials’ Twitter accounts to stay updated. And a reading recommendation for those who want to learn even more is a textbook titled 21st Century Global Health Diplomacy published by World Scientific. 

Angela Lu (NHS’20) is a senior in the School of Nursing and Health Studies studying in healthcare Management and Policy and Public Health. She is currently a Global Health Officer Intern at the Office of Global Affairs in the US Dept. of Health and Human Services. She is also a Student Fellow with the Global Health Institute at Georgetown University.