THE POTENTIAL IMPACT OF EXPANDING TARGET AGE GROUPS FOR POLIO IMMUNIZATION CAMPAIGNS

Radboud J Duintjer Tebbens^1*, Dominika A Kalkowska¹², Steven GF Wassilak³, Mark A Pallansch⁴, Stephen L Cochi³ and Kimberly M Thompson¹⁵

·         * Corresponding author: Radboud J Duintjer Tebbens rdt@kidrisk.org

¹ Kid Risk, Inc, 10524 Moss Park Road, Site 204-364, Orlando, FL 32832, USA

² Delft Institute of Applied Mathematics, Delft University of Technology, Delft, The Netherlands

³ Global Immunization Division, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA, USA

⁴ Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA

⁵ University of Central Florida, College of Medicine, Orlando, FL, USA

BMC Infectious Diseases 2014, 14:45  doi:10.1186/1471-2334-14-45

The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/1471-2334/14/45

© 2014 Duintjer Tebbens et al.; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Abstract

Background

Global efforts to eradicate wild polioviruses (WPVs) continue to face challenges due to uninterrupted endemic WPV transmission in three countries and importation-related outbreaks into previously polio-free countries. We explore the potential role of including older children and adults in supplemental immunization activities (SIAs) to more rapidly increase population immunity and prevent or stop transmission.

Methods

We use a differential equation-based dynamic poliovirus transmission model to analyze the epidemiological impact and vaccine resource implications of expanding target age groups in SIAs. We explore the use of older age groups in SIAs for three situations: alternative responses to the 2010 outbreak in Tajikistan, retrospective examination of elimination in two high-risk states in northern India, and prospective and retrospective strategies to accelerate elimination in endemic northwestern Nigeria. Our model recognizes the ability of individuals with waned mucosal immunity (i.e., immunity from a historical live poliovirus infection) to become re-infected and contribute to transmission to a limited extent.

Results

SIAs involving expanded age groups reduce overall caseloads, decrease transmission, and generally lead to a small reduction in the time to achieve WPV elimination. Analysis of preventive expanded age group SIAs in Tajikistan or prior to type-specific surges in incidence in high-risk areas of India and Nigeria showed the greatest potential benefits of expanded age groups. Analysis of expanded age group SIAs in outbreak situations or to accelerate the interruption of endemic transmission showed relatively less benefit, largely due to the circulation of WPV reaching individuals sooner or more effectively than the SIAs. The India and Nigeria results depend strongly on how well SIAs involving expanded age groups reach relatively isolated subpopulations that sustain clusters of susceptible children, which we assume play a key role in persistent endemic WPV transmission in these areas.

Conclusions

This study suggests the need to carefully consider the epidemiological situation in the context of decisions to use expanded age group SIAs. Subpopulations of susceptible individuals may independently sustain transmission, which will reduce the overall benefits associated with using expanded age group SIAs to increase population immunity to a sufficiently high level to stop transmission and reduce the incidence of paralytic cases.

TRENDS IN THE RISK OF U.S. POLIO OUTBREAKS AND POLIOVIRUS VACCINE AVAILABILITY FOR RESPONSE

Public Health Reports

Association of Schools of Public Health

Kimberly M. Thompson, ScD, Gregory S. Wallace, MD, MS, MPH, [...], and Steven G. F. Wassilak, MD

Synopsis below; full text, with figures, is at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3234395/

Objectives

The United States eliminated indigenous wild polioviruses (WPVs) in 1979 and switched to inactivated poliovirus vaccine in 2000, which quickly ended all indigenous live poliovirus transmission. Continued WPV circulation and use of oral poliovirus vaccine globally allow for the possibility of reintroduction of these viruses. We evaluated the risk of a U.S. polio outbreak and explored potential vaccine needs for outbreak response.

Methods

We synthesized information available on vaccine coverage, exemptor populations, and population immunity. We used an infection transmission model to explore the potential dynamics of a U.S. polio outbreak and potential vaccine needs for outbreak response, and assessed the impacts of heterogeneity in population immunity for two different subpopulations with potentially low coverage.

Results

Although the risk of poliovirus introduction remains real, widespread transmission of polioviruses appears unlikely in the U.S., given high routine coverage. However, clusters of un- or underimmunized children might create pockets of susceptibility that could potentially lead to one or more paralytic polio cases. We found that the shift toward combination vaccine utilization, with limited age indications for use, and other current trends (e.g., decreasing proportion of the population with immunity induced by live polioviruses and aging of vaccine exemptor populations) might increase the vulnerability to poliovirus reintroduction at the same time that the ability to respond may decrease.

Conclusions

The U.S. poliovirus vaccine stockpile remains an important resource that may potentially be needed in the future to respond to an outbreak if a live poliovirus gets imported into a subpopulation with low vaccination coverage.

U.S. public health policies generally focus on maintaining high levels of routine coverage with recommended vaccines for 16 vaccine-preventable diseases that remain well-controlled or eliminated.¹ Figure 1 provides a timeline of several key events related to polio vaccine use in the United States.^2–13 Increased reliance on inactivated poliovirus vaccine (IPV)-containing combination vaccines continues to decrease the supply of stand-alone IPV, which dropped from a market share of 100% in 2000–2002 to approximately 60%–65% in 2006–2008 to approximately 30% in 2009 (Unpublished data, Centers for Disease Control and Prevention [CDC], July 2010). CDC maintains the U.S. Pediatric Vaccine Stockpile to ensure an adequate supply of vaccines to meet unanticipated needs, including use in the event of outbreaks or vaccine shortages.

THE CASE FOR COOPERATION IN MANAGING AND MAINTAINING THE END OF POLIOMYELITIS: STOCKPILE NEEDS AND COORDINATED OPV CESSATION

Kimberly M. Thompson, ScD, Radboud J. Duintjer Tebbens, PhD

Abstract below; full text is at http://www.medscape.com/viewarticle/578396

Context: Achieving successful eradication of a disease requires global cooperation to obtain a shared goal. Coordination of the endgame may seem an obvious requirement for success, but that does not ensure that cooperation will occur.

Objective: To analytically explore the need for cooperation to maintain global polio eradication specifically related to creation of a global polio vaccine stockpile and coordination of oral poliovirus vaccine (OPV) cessation.

Design: Using risk and decision analysis and game theoretical concepts, we modeled the importance of global cooperation in managing the risks associated with polioviruses for a time horizon of 20 years after successful global disruption of circulation of wild polioviruses.

Results: Countries may wish to avoid the financial costs of vaccination and risks for vaccine-associated paralytic polio following eradication of wild polioviruses, which may lead them to reduce their use of OPV. However, reducing or stopping vaccination too soon and without coordination poses serious risks, including the possibility of reimportation of wild polioviruses and the possibility of vaccine-derived polioviruses. Analysis of the risks for potential outbreaks suggests the need for creation and maintenance of a global stockpile of vaccine for outbreak response. Game theoretical considerations show that coordination of OPV cessation optimizes expected costs and risks globally, despite the potential perceived incentives for countries to stop OPV earlier or later than other countries, or to continue OPV use indefinitely.

Conclusions: This article makes the strong case for global cooperation on risk management and suggests that even though individual countries may perceive their own risks as small, risks at the global level warrant cooperative action and coordination of OPV cessation.

THE RISKS, COSTS, AND BENEFITS OF POSSIBLE FUTURE GLOBAL POLICIES FOR MANAGING POLIOVIRUSES

Am J Public Health. 2008 Jul;98(7):1322-30. doi: 10.2105/AJPH.2007.122192. Epub 2008 May 29.

Thompson KM¹, Tebbens RJ, Pallansch MA, Kew OM, Sutter RW, Aylward RB, Watkins M, Gary HE Jr, Alexander J, Jafari H, Cochi SL.

Abstract below; full text is at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2424088/

OBJECTIVES:

We assessed the costs, risks, and benefits of possible future major policy decisions on vaccination, surveillance, response plans, and containment following global eradication of wild polioviruses.

METHODS:

We developed a decision analytic model to estimate the incremental cost-effectiveness ratios and net benefits of risk management options for polio for the 20-year period and stratified the world according to income level to capture important variability between nations.

RESULTS:

For low-, lower-middle-, and upper-middle-income groups currently using oral poliovirus vaccine (OPV), we found that after successful eradication of wild polioviruses, OPV cessation would save both costs and lives when compared with continued use of OPV without supplemental immunization activities. We found cost-effectiveness ratios for switching from OPV to inactivated poliovirus vaccine to be higher (i.e., less desirable) than other health investment opportunities, depending on the actual inactivated poliovirus vaccine costs and assumptions about whether supplemental immunization activities with OPV would continue.

CONCLUSIONS:

Eradication promises billions of dollars of net benefits, although global health policy leaders face difficult choices about future policies. Until successful eradication and coordination of posteradication policies, health authorities should continue routine polio vaccination and supplemental immunization activities.

ERADICATING POLIO: THE DOLLARS AND SENSE

Kimberly M. Thompson, ScD

October 15, 2007

Also at http://www.medscape.com/viewarticle/563895

For those who do not remember when polio terrified families and children in iron lungs-filled hospital wards, the concept of spending money on polio now might seem strange, particularly in the face of so many arguably competing opportunities to invest in health. But wild polioviruses continue to circulate in a few places, and this is a critical time in the fight to eradicate polio.

Hopefully, we are now at the bitter end of global eradication of wild polioviruses, with annual cases of paralytic polio down globally from an estimated 350,000 in 1988 to under 2000 today.^[1] Following successful eradication, we must choose wisely among the many policy options^[2] that will determine our future risks, costs, and benefits.^[3-8] But first, we need to complete polio eradication. We cannot declare success before the war is won.

Part of the challenge arises from the reality that success to date toward global eradication means that people see fewer paralytic polio cases, and this decreases the perception of polio as a health threat. "Out of sight, out of mind." But polio could come back with a vengeance, and it will most likely be much cheaper, and better from a health perspective, to finish polio eradication now instead of trying to control the disease and keep it at the current low level of cases.^[9]

We can afford global polio eradication. In the US, the savings from our historical investments in domestic polio control and elimination efforts exceeds an estimated $180 billion on net.^[10] In other words, preventing paralysis and saving lives saves dollars and makes sense. If we can achieve polio eradication, it will represent an important step toward maximizing global health.

That is my opinion. I am Dr. Kimberly Thompson, Associate Professor and Director of the Kids Risk Project at the Harvard School of Public Health.