The global effort to eradicate wild poliovirus has made significant strides. Type 2 was declared eradicated in 2015 and type 3 in 2019. Only type 1 of the wild polio virus remains. However, a new challenge has emerged in the form of vaccine-derived polio. Despite the success in reducing wild polio cases to only 30 in 2022, vaccine-derived strains led to 859 cases across 24 countries during the same time period. Vaccine-derived polio, while extremely rare, can occur when the weakened poliovirus used in oral vaccines reverts to virulence.
Novel Vaccines Target Vaccine-Derived Outbreaks
Researchers led by Andrew Macadam at the National Institute for Biological Standards and Control in the United Kingdom have developed new oral polio vaccines that minimize the risk of vaccine-derived outbreaks for virus types 1 and 3. Leveraging genetic engineering techniques, the researchers designed the new vaccines to prevent the attenuated virus from regaining virulence. Tested successfully in mice, they are currently undergoing human trials. If proven effective, they could join the new type 2 polio vaccine known as nOPV2 to potentially protect against vaccine-derived outbreaks from all three poliovirus subtypes.
Eradication Challenges and Causes of Vaccine-Derived Polio Resurgence
While the nOPV2 vaccine has been administered to millions of children across 30 countries, it has experienced occasional reversions to virulence, hindering progress. The resurgence of vaccine-derived polio stems from various factors, including disruptions caused by the COVID-19 pandemic, natural disasters, and political conflicts. In addition, researchers noted that outbreak risk increased in places where public health officials chose to wait and adopt the newer vaccines instead of using available older options.
Complexities in Polio Campaigns and Transition Challenges
The transition of polio eradication efforts from the Global Polio Eradication Initiative (GPEI), a broad partnership that includes the World Health Organization (WHO), to national programs has encountered difficulties. The transfer has led to funding gaps, loss of expert staff, governance issues, and waning morale in some countries. An Independent Monitoring Board commissioned by the GPEI has criticized aspects of the transition process. In response, the WHO has reevaluated the plan and is implementing a more calculated approach.
The Importance of Coordinated Efforts and Future Strategies
Transitioning polio management to national control is essential in the long term, but it is important that the process does not compromise progress. The commitment to eradicate vaccine-derived polio can be affected by the perception that wild poliovirus is nearly eradicated. As outlined in a Nature editorial, continued vaccine research, technology advancement, and the deployment of vaccines through well-funded and motivated local programs are crucial to defeating vaccine-derived polio.
Technologies to accelerate poliovirus detection and the development of alternative vaccine strategies are promising tools in this effort. For example, although it can currently take weeks to confirm the presence of poliovirus in wastewater, researchers are developing technologies to decrease this interval. In addition, work is ongoing to develop innovative vaccine alternatives, including vaccines that would contain no viral genomic material.
Striving Toward a Polio-Free Future
To truly overcome the challenge of vaccine-derived polio, a combined approach including scientific innovation, comprehensive public health initiatives, and efficient distribution is needed. Learning from past successes, such as smallpox eradication, and addressing the specific challenges of vaccine-derived polio will be crucial in finally eliminating this threat. The journey towards a polio-free world requires vigilance, adaptability, and global cooperation, ensuring that vaccine research translates into on-the-ground action.
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