Switching from OPV to IPV: are we behind the schedule in Latin America?

Abstract and Introduction

Abstract

Oral polio vaccine (OPV) has been an effective strategy since it was initiated almost five decades ago. However, concern regarding its collateral effects has been increasing in recent years among the scientific and policymaker community, since it has proved to be of risk for immunocompetent and immunocompromised individuals by causing cases and even outbreaks of poliomyelitis disease in countries where the virus is not circulating. Enhanced-potency inactivated polio vaccine (IPV), a safer, effective and inexpensive vaccine, has been available for the past couple of decades. Different points of view have emerged regarding stopping the use of OPV to start routine general IPV but, despite the evidence of OPVs derived and associated with unnecessary poliomyelitis cases, Central and South America are still lacking a strategy in place to make the switch from OPV to IPV, and there are no leading efforts to start this strategy. This review gives some evidence-based elements to help raise criteria regarding the best vaccine to choose and highlights the current need for strategic planning in Latin America to avoid more vaccine-associated paralytic poliomyelitis cases.

Introduction

Following the declaration of the eradication of smallpox in 1980 by the World Health Assembly, the Global Poliomyelitis Erradication Initiative (GPEI) of the WHO was initiated under four strategies: regular vaccination with oral polio vaccine (OPV); supplementary immunization activities (e.g., national immunization days); surveillance of wild virus through viral report and analysis of flaccid paralysis cases; and immunization focalized on house-to-house OPV 'mop-up'. The GPEI has been very successful; by 1999, it had reduced 99% of poliomyelitis cases all over the world, it had interrupted the circulation of type 2 wild poliovirus and it permitted that three of the six WHO's regions be declared polio free.

For the GPEI to be fully and successfully completed, it first has to accomplish three goals: the certification of eradication of poliomyelitis all over the world, control and preservation of the still-existing wild virus, and the interruption of polio vaccination. However, the accomplishment of these objectives has been threatened by several recent events:

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  In 1995, researchers from the Pan American Health Organization reported 139 cases of paralytic polio associated with the oral vaccine within a period of 3 years in the region of the Americas;
  
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  In 2000, the first poliomyelitis outbreak due to a circulating vaccine-derived poliovirus (cVDPV) was reported, causing the paralysis of approximately 21 children in the Dominican Republic and Haiti. Since then, the importance of the vaccine-derived virus emerged, especially on immunosuppressed patients (immunodeficiency-related vaccine-derived poliovirus [iVDPV]). Another case was recently reported in Argentina;
  
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  In the middle of 2003, two states in Nigeria decided to suspend the OPV, a decision that not only led to large national outbreaks, but also resulted in the exportation of wild virus to more than 20 countries, a tragedy that caused the paralysis of thousands of children;
  
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  In 2006, there were cases of vaccine-derived virus without a clear history; these were classified as ambiguous vaccine-derived poliovirus (aVDPV);
  
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  During 2009 and for the fifth consecutive year, Nigeria reported a sustained outbreak of type 2 cVDPV, which caused the paralysis of more than 290 children, 146 of them occurring in 2009. This outbreak is still out of control.
  

Situations such as those described previously, plus other factors that will be explained in more detail later, have placed doubt as to whether the final eradication of this disease will be possible, and has also brought into discussion the role of the two available polio vaccines.