International cooperation in desease control in the face of evolutionary risks

CONTROL OF IMMUNIZING INFECTIONS

Immunization Week: What is the purpose of vaccination?
Interview by Olivier Monod, published on 25/04/2014 at 16:20

Should everyone be vaccinated or only the most contagious? How can countries cooperate? For Vaccination Week, Petra Klepac, a researcher from the University of Cambridge supported by the AXA Research Fund, answers a few questions for “Chercheurs d'actu.”

In French: https://www.lexpress.fr/sciences-sante/sante/a-quoi-sert-la-vaccination_1511433.html

Can vaccines help completely eradicate diseases?
It mostly depends on the characteristics of the pathogen responsible for the disease. Smallpox could be eliminated because it was a disease that only affected humans. However, it is more complex to eradicate a disease whose vector spends part of its life cycle in other species, such as malaria for example, which is transmitted by mosquitos.

What percentage of the population needs to be vaccinated to prevent a disease like the flu from spreading?
It depends on the rate of transmission. A person with the flu will infect fewer than 2 people. Statistically, it is therefore enough to protect half of the population to prevent an epidemic. Measles poses more of a threat. A person with measles will infect up to 15 people. This means that 14 out of every 15 people in the population need to be vaccinated. However, these calculations assume that the vaccine provides lifelong immunity. But reality is not as simple. Sometimes several doses of the vaccine are needed, sometimes boosters are necessary, sometimes the pathogen mutates... Ultimately, fighting a disease is a balance between the cost of the disease and the cost of protection…

Any less costly strategies for fighting a disease?
Is it better to protect people in whom the disease is more severe or people who are the most likely to contract the disease and spread it, without it necessarily having any serious consequences for them? In the case of the flu, children spread the virus, but the symptoms are particularly severe in the elderly. Models show that we can stop the disease with less vaccination if we focus on protecting children.

So the rationale applies at the national or international level, rather than the individual level…
Indeed. At the individual level, vaccination is an excellent way to protect yourself from a disease. At the population level, it is a weapon for fighting a pathogen and achieving “collective immunity.”

Diseases are transnational phenomena. How can countries collaborate in terms of vaccination?
Policies are implemented at the national level. Models show that it would be more effective and less costly to pool efforts and resources. However, there is no supra-national structure to provide overall coordination. The problem is actually the same for climate issues… This can have harmful consequences. The influx of migrants caused by the Syrian conflict has led to a return of polio in areas where it had previously disappeared…
Right now, I am working with Bryan Grenfell and Ramanan Laxminarayan to determine whether the “theory of international agreements,” developed for environmental matters, can be applied to international health policy

The path to research
Petra Klepac could never decide between mathematics and biology. “That explains why I work on biological questions with mathematical tools. Disease dynamics uses concepts from several disciplines, which makes it very interesting.” In a context of restricted funding for research, Petra deems herself “fortunate” to be supported by the AXA Research Fund. “Today, research is an uncertain and competitive field. We need to be very mobile and ready to move to another continent if necessary to pursue our work.”

International cooperation in control of immunizing infections

Control and elimination of infectious diseases requires coordination of efforts on international, regional and global levels. This is particularly the case in an increasingly interconnected world where human mobility could promote free-riding in vaccination efforts between populations resulting in a below-optimal vaccination coverage. Without an international body that can impose and implement a control strategy on a global level, the enforcement of control efforts is left to individual countries, but little is known about how these might function in the context of control of infectious diseases on a large spatial scale.
My research combines epidemiological dynamics with the game theory of international agreements to find ways to increase cooperation and reach the regional vaccination coverage necessary for efficient control of infectious diseases and possibly their elimination. Specifically, I look at whether formation of voluntary coalitions can utilize the transnational benefits of infectious disease control in order to enhance regional and global elimination interventions. Indeed, with the help of international agreements, countries can achieve higher, more consistent, and more uniform vaccination coverage even in the absence of external enforcement. Surprisingly, this higher vaccination coverage in the coalition is achieved at a lower cost than when countries are acting independently.
In the second part of the project I will shift the focus on international control and improvement of interventions for pathogens in the face of evolutionary risks, where selection for resistance or higher virulence can undermine the control efforts in the long run.
This project provides a novel framework for evaluating regional control and elimination strategies and has results that have important implications in the public health context, with relevance for both human and animal diseases.

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